235

OF THEIDLLS

THE LOWER CORALLIAN ROCKSYORKSIllRE COAST AND HACKNESS

By VERNON WILSON, Ph.D., M.Sc., DJ.C.

[Received 25th November, 1948}

[Read 7th January, 1949)

CONTENTSPAGE

INTRODUCTION 235GENERAL SUCCESSION, LITHOLOGY AND FAUNA 237STRATIGRAPffiCAL DETAILS :

(a) The Coast between Filey and Scarborough 240(b) The Hackness Hills 249

VARIATIONS IN GRAIN SIZE AND THE RANGE AND DISTRIBUTION OF THESPICULES OF Rhaxella perforata Hinde 254

THE PALAEOECOLOGY OF THE HAMBLETON OOUTE REEF AND ASSOCIATEDSEDIMENTS 257

GEOLOGICAL HISTORY OF THE AREA:(a) Conditions of Sedimentation ... 261(b) Palaeogeography 264

PALAEONTOLOGICAL NOTES ON THE CALClSPONGlAE... 265REFERENCES 268DISCUSSION 270

SUMMARY.-Sections in the Lower Corallian rocks on the coast at Fileyand Scarborough and in the Hackness Hills are described. Evidences ofrepeated intraformational erosion in the Hambleton Oolite beds at Filey arerecognised and the structures known as "fucoids" occurring at the bases ofmany of the beds are thought to be weathered-out infillings of sun-cracks. Thedetrital quartz grains diminish in profusion and size towards the north-west,implying derivation from the east or south-east. The palaeoecology of theHambleton Oolite Coral-Sponge reef in the Hackness Hills is discussed inrelation to the faunas of the equivalent beds at Scarborough and Filey. Newspecies of Holcospongia and Peronidel/a are also described.

INTRODUCTIONTHROUGHOUT the main northern outcrop of the Corallian Rocks

across North-East Yorkshire there is a gradual attenuationfrom west to east. In the coastal area this thinning is particularlymarked in the Lower Corallian Beds (Lower Calcareous Grit,Hambleton Oolites and Middle Calcareous Grit) towards the south­east from the Hackness Hills to Filey, and it is accompanied byconsiderable variations in the lithology and in the character anddistribution of the fossils.

In the following pages these lithological and faunal variationsare discussed in relation to the probable nature of the sea floorand the conditions of sedimentation under which the depositsaccumulated. There is evidence to show that at the end of LowerCalcareous Grit times and during the succeeding HambletonOolite and Middle Calcareous Grit episodes the sea was remarkably

PROC. GEOL. Assoc., VOL. 60, PART 4, 1949. 17

236 VERNON WILSON

shallow in this area and it is suggested that there may have beenlow lying land at no great distance to the south-east.

The Corallian rocks in this area aroused the interest of WilliamSmith during his six years residence at Hackness, and in describingthem in 1829 [36*] he gave a remarkably accurate account of thelocal succession in that district, recognising the peculiar and prom­inent part played by the calcareous sponges in the early coral­sponge reef of the Hambleton Oolite episode. His succession is asfollows :-

LimestoneCoralline Spongite Coral Bed

Oolite Grey or Wall stoneReddish yellow sand, corresponding with the indurated sand

Calcareous exposed on the north side of Scarborough Castle HillGrit Cherty bed of stone which forms the plains of the moors

and the high well-defined edge of the Tabular HillsFreestone beds below this

Oxford Clay

In describing the Coral Bed he says, it "is a more earthy bedreposing on the greystone, only about 6 feet containing lumps ofcoral and small spongites, which distinguish it from the coral overthe limestone" ; from these last four words it is evident that Smithrealised this coral rag to be quite distinct from, and earlier than,the later coral rag of the Higher Osmington Oolites.

John Phillips [30] has also detailed bed by bed the varioussections between Filey and Scarborough, recognised the characteris­tic fossils and described and figured many new species.

In spite of the care with which Blake and Hudleston recordedsections and other evidence [12], it is apparent in so far as thisarea is concerned that they were not entirely satisfied with theirinterpretations. For example, they state [12], p. 385 " the sectionat Filey still remains somewhat problematical," and again a fewlines farther on, in referring to the section at Scarborough CastleHill, "this section is more imperfect than that at Filey" ; stillfarther on (p. 386) they state, "The Middle Calcareous Grit israther irregular and uncertain. It seems to break out in FileyBrigg."

The official geological survey was carried out principally byBarrow and Fox-Strangways, the accounts of these rocks by thelatter were largely based on the findings of Blake and Hudlestonand contain little new information.

During the present investigation all available sections havebeen re-examined and recorded in detail, new evidence broughtforward and new collections of fossils made, and in the ensuingpages an attempt is made to resolve the difficulties which wereencountered by Blake and Hudleston.

• For list of References see p. 268.

CORALLIAN ROCKS OF YORKSHIRE COAST 237

Here, I should like to express my thanks to Dr. W. J. Arkell,F.R.S., for his ever willing help and encouragement in these prob­lems in Yorkshire; he has read this manuscript and offered manyvaluable comments and useful suggestions which it is a pleasure toacknowledge.

GENERAL SUCCESSION, LITHOLOGY AND FAUNAThe general sequence in the area under discussion comprises

the three lower sub-divisions of the Corallian and is summarisedin the following table :-

HacknessZones Filey Scarborough District

Thick brown Unfossiliferouswedge-bedded ferruginous

Perisphinctes sandstones Absent sandy lime- MIDDLEplicati/is with lenses of stones with CALCAREOUS

detrital lime- fine shell GRITstone,15ft. debris and

scatteredooliths, 20ft.

Cardioceras Calcareous Impure ooliticcordatum ss. gritstones with limestones, Oolite, 30ft.

sun-cracked 26ft. HAMBLETONlayers and Gritstones and Coral-Sponge OOLITE

Cardioceras indurated detrital lime- Rag, 11ft. SERIEScosticardia beds; 28ft. stones, 28ft. Brown sandy

detrital lime-stones, 25ft.

Cardioceras "Ball Beds," 10 to rsn.bukowskii LOWERCALCAREOUS

Cardioceras Hard cherty band, 3 to 7ft. GRITpraecordaturn Massive buff gritstones, 50 to 115ft.

Lithologically these rocks show every kind of deposit from finearenaceous types to pure oolites with a phase of reef growth in thelower part of the Hambleton oolites in the Hackness neighbourhood.

The Lower Calcareous Grit.-The Lower Calcareous Grit consistsmainly of fine-grained calcareous gritstones and is sud-divided asfollows :-

3. The " Ball Beds." (bukowskii zone) 10-18 feet thick. In­coherent soft ferruginous sandstones containing hard lime­stone doggers varying in size from a few inches to 3 or 4 feetin diameter occurring sporadically or in lines and layers.

2. Hard blue-grey cherty gritstone band, 3-7 feet thick.1. The main mass of the calcareous grit (praecordatum zone),

40-115 feet thick, comprising thick beds of hard buff

238 VERNON WILSON

gritstones, often blue centred, with no trace of currentbedding. These beds pass down gradually without anysharp line of demarcation into the underlying Oxford Clay.

The whole series is lithologically constant along the coast andthroughout the Hackness Hills. The limestone doggers in the" Ball Beds" are fairly fossiliferous and at Scarborough and Fileywhere they are well exposed they have yielded spicules of Rhaxellaperforata, Chlamys fibrosa, Exogyra nana, Astarte ovata, Meleagrin­ella ovalis, Trigonia triquetra, Rhynchonelloidea thurmanni and

Vale of· PicJter.tng

B. =BROXA

H. = HACKNESSSC.=SCALBYSI·=SILPHO

SU.=SUFFIELD

FlO. 4O.-SKETCH-MAP OF THE YORKSHIRE CoAST between Fileyand Scarboroughand the Hackness Hills (shaded) area. (Scale about 4 miles to 1 inch.)

Nucleolites scutatus. In the main mass of the grit, below the., Ball Beds," well exposed at Scarborough Castle Hill, CaytonBay and in the Gristhorpe Cliffs spicules of Rhaxella perforata arevery abundant, and Rhynchonelloidea thurmanni, Chlamys fibrosa,Astarte ovata, Exogyra nana, Trigonia triquetra, Meleagrinellaovalis, Gryphaea dilatata, Lima laeviuscula, Gervillia aviculoides,Modiola bipartitus, Isognomon quadrata, Pinna lanceolata, Collyritesbicordatus, Pachyteuthis abbreviatus and Serpulae are common.

The Hambleton Oolites.-Throughout their main outcrop in theTabular Hills these rocks are mainly oolites but in this area theyvary in lithology, thickness and fauna. The change from the sandy

CORALLIAN ROCKS OF YORKSHIRE COAST 239

" Ball Beds" with their limestone doggers at the top of the LowerCalcareous Grit to the succeeding impure limestones is gradual.These calcareous gritstones and impure limestones are 28 feet thickat Filey and the uneven indurated character of the lower beds andoccasionally at higher levels indicates intra-formational erosion.The following ammonites have been recorded from these beds :­Cardioceras (Subvertebriceras) costellatum and C. (Cardioceras)costicardia. Farther north, at Scarborough Castle Hill, the bedshave thickened to 54 feet, of which the upper 26 feet are impureoolitic limestones while the lower beds are made up of variablegritstones and hard detrital limestones containing Perisphinctesbernensis.

In the Hackness district five miles west-north-west of Scar­borough the oolites in the upper part have increased to 30 feet,probably their full development hereabouts; below these is a welldeveloped coral-sponge reef whose maximum thickness is 11 feet,which is underlain by 25 feet of brown sandy detrital limestones.The occurrence of a reef deposit at this low horizon in the HacknessHills is unique in the British Corallian sequence.

While the Lower Calcareous Grit yields a fauna somewhat poorin species the sub-divisions of this period contain a fair abundanceof characteristic forms. The majority of the species present in theunderlying gritstones persist into the lower beds of the HambletonOolites, but new forms, many of which are small, appear and tosome extent herald the very fossiliferous Osmington Oolites of laterdate. It was, however, in the Hackness reef where life was mostvaried, prolific and localised. Lithologically this reef consists ofan intimate mixture of large and small lenses of compound coralwith large numbers of calcareous sponges, terebratulids, reef detritusand fine mud, together with an abundant fauna of molluscs and otherfossils different in many respects from those associated with laterepisodes of coral growth. Most of the corals belong to specieswhich take part in the widespread developments of reefs at higherCorallian horizons in England. This community of corals, spongesand terebratulids is an interesting faunal association not foundelsewhere in this country, and here also is the earliest occurrenceof a small molluscan fauna, comprising Lima zonata , Lithophagainc/usa, Chlamys nattheimensis, Lopha gregarea and Xysterellamuricata, confined to the reef habitat.

In the coastal area, particularly at Filey, in addition to theammonites mentioned above, the gritty limestones also contain anabundant fauna in which shallow water forms predominate. Be­sides many of the calcareous sponges and terebratulids characteristicof the Hackness reef there are the remains of the crinoids Milleri­crinus echinatus and Pentacrinus, echinoderms are represented byPygurus pentagonalis, Pseudodiadema versipora, Acrosalenia decor­ata, Paracidaris jiorigemma and plates of the starfish Astropecten,

240 VERNON WILSON

together with hosts of the ubiquitous little Exogyra nana, Lophagregarea, Gryphaea di/atata, Gervi/lia aviculoides and countlessentangled knots of Serpula intestinalis and S. tricarinata, all indica­tive of very shallow water.

The Middle Calcareous Grit.-In the Hackness Hills the Hamble­ton Oolite is succeeded by 20 feet of unfossiliferous ferruginoussandy limestones containing a high proportion of comminutedshell debris and scattered ooliths. These beds are rarely exposedat the present time but they give rise to a rich reddish brown loamysoil carrying rubble of the underlying rock; this is very noticeablearound the village of Silpho.

On the coast beds of this age are only present at Filey, wherethey occur as thick brown wedge-bedded sandstones amounting to15 feet; they contain thin seams and lenses of detrital shelly ooliticlimestone which tend to be more common in the upper part of theseries. Fossils are not very common in these beds except for suchpersistent forms as Gervillia aviculoides, Isognomon quadrata,Chlamys fibrosa, Gryphaea di/atata and Meleagrinella ovalis.The thin limestones yield faunas which include such commonforms as Trigonia hudlestoni, Lima laeviuscula and Astarte ovata.

In order to appraise the full significance of the variations inthickness, lithology and faunas of the Corallian rocks in this areait is now necessary to examine in detail all the available sectionswhere they are displayed from Filey Bay northward to ScarboroughCastle Hill and in the nearby Hackness Hills to the north-west(Fig. 40).

STRATIGRAPIllCAL DETAILS(a) The Coast between Filey and Scarborough

The wide, smooth, concave outline of Filey Bay is carved out ofthe Kimmeridge Clay and its unstable covering of 125 feet ofBoulder Clay cliffs ; on its north side it terminates abruptly againstthe straight southern flank of a long promontory of hard Corallianrocks overlain for about half its length by 100 feet of boulder clay.The landward drift-covered part of this peninsula is known asFiley Carr Naze, and the sea-swept part of it to the east is known asthe Brigg. The Corallian beds dip southward towards the bay atgo, and within a few yards of the low-tide mark on the south side theyare truncated by a strong fault which brings down the KimmeridgeClay into the floor of the bay (Fig. 41).

The foundations of the Brigg below the sea are formed by theLower Calcareous Grit while the Hambleton Oolite beds andMiddle Calcareous Grit form the exposed craggy part above thewater; the latter also forms the greater part of the south side of theCarr Naze. Thin basal beds of the Osmington Oolite, much brokenand churned up in Glacial times, form a thin outcrop beneath thesteep boulder clay cliffs all round the Carr Naze. Of all the beds

~BOULDER CLAY~ OSMINGTON OOLITE

MIDDLE CALCAREOUS GRIT

HAMBLETON OOLITE

LOWER CALCAREOUS GRIT

~....

242 VERNON WILSON

displayed on the north side of the Carr Naze the " Ball Beds" atthe top of the Lower Calcareous Grit offer the least resistance toerosion by the sea, and as the limestone doggers are loosened andfreed from their matrix their movement by the sea further assistserosion. As a result of this action the overlying beds have beenundermined in four places and have consequently collapsed andgiven rise to four large open marine caves or "doodles." It is onthis north side of the Carr Naze that the whole sequence is mostcompletely exposed and accessible for bed-by-bed examination.The following details and measurements have been recorded at theentrance to the first " doodle" (Plate 9).

SECTION ON THE NORTH SIDE OF THE CARR NAZE, FILEYOSMINGTON OOLITE SERIES ft. ins.

34. Hard broken, detrital oolitic limestones covered by boulder clay.Seen to the best advantage on the south side of the Carr Naze .. 14 0Pleuromya uniformis, Lima rigida, Chlamys splendens, andNucleolites scutatus.

33. Loose, nodular brash .. 0Ostrea quadrangularis, Chlamys splendens, Nucleolites scutatusand Holectypus depressa

32. White detrital shelly limestone 2 3Gryphaea dilatata and Trigonia sp.

MIDDLE CALCAREOUS GRIT31. Thinly bedded, soft sandstone with nodules of shelly material

in the upper part 2ft. 6ins. to 2 930. White detrital nodular limestone, shelly and oolitic in the upper

part; this bed is packed with serpulid tubes 6Trigonia densicostata Lopha genuflectaGervillia aviculoides Astarte ovataMeleagrinella ovalis Pseudomelania heddingtonensisOstrea quadrangularis Xysterella muricataCtenostreon proboscideum Nucleolites scutatusLima laeviuscula Serpula intestinalisLima rigida

29. Thinly bedded brown fissile sandstone with" fucoids" in the lowerpart; the upper 4 inches consists of fine shell debris 2 0

Astarte ovata Gryphaea dilatataGoniomya literata Pleurotomaria munsteriPleuromya uniformis

28. Thin band of white porous grit 6 ins. to 9Trigonia densicostata Lima rigidaGervillia aviculoides Xysterella muricataPleuromya uniformis and a fragment of a cordateGryphaea dilatata ammoniteChlamys splendens

27. Thick bed of brown sandstone 2 3Goniomya literata Lucina sp.Pinna lanceolata

26. Thick bed of brown sandstone, the upper 9 inches to I foot tendingto be a shelly limestone, from which the following fossils arerecorded 4 ft. to 5 0

Pholadomya aequalis Lima rigldaGervillia aviculoides Astarte ovataMeleagrinella ovalis Xysterella muricata

CORALLIAN ROCKS OF YORKSIDRE COAST 243

Trigonia densicostata Holectypus depressaGryphaea dilatata Serpula intestinalisPleuromya uniformis

25. Peculiar false-bedded buff sandstone with lines of small masses ofcoarser grit 2 0

HAMBLETON OOLITE SERIES24. Hard buff grit with nodules containing spicules of Rhaxella

perforata. Gryphaea dilatata .. 923. Hard sandstone full of .. fucoids," and an occasional dogger

containing spicules of Rhaxella perforata 9 ins. to 0Lopha gregarea Gryphaea dilatataGoniomya literata Rhaxella perforata

22. Brittle gritty nodular limestone with scattered ooliths 7 ins. to 9Lopha gregarea Lima rigldaAstarte ovata Pseudomelania heddingtonensis

21. Thick brown sandstone with dark fucoid-like masses 9Pinna lanceolata Chlamys splendens

20. Hard cherty grey gritstone, composed of Rhaxella spicules 8 ins. to 1 019. Brown, limestone-centred sandstone 1 ft. 3 ins. to 2 0

Meleagrinella ovalis Gervillia aviculoidesTrigonia densicostata Lima rigida

18. Grey limestone band 6 ins. to 10Pleuromya uniformis Pholadomya aequalis

17. Brown sandstone, largely greystone centred ; sandy in upper andlower parts with fucoids developed .. 1 ft. 1 in. to 3

Gervillia aviculoides Nue/eolites scutatus16. Thin, hard-centred sandstone with Rhaxella spicules 6 ins. to 1015. Thin sandstone with dark fucoid-like nodules 9 ins. to 1 014. Hard, blue, gritty limestone, with coarse and fine shelly material

in the upper part 2 0Lopha T genuflecta Gryphaea dilatataAstarte ovata Rhynchonelloidea thurmanniMeleagrinella ovalis

13. Grey-white, gritty limestone, with fucoids in the lower part ; muchshell debris towards the top 2 ft. to 2 3

Rhynchonelloidea thurmanni12. Hard, blue gritty limestone, the lower 6 inches of which is a sand-

stone with fucoids .. 2 ft. 3 ins. to 2 6Camptonectes lens Lima rigidaGervillia aviculoides Rhynchonelloidea thurmanni

11. Thick brownsandstone with uneven top and base. In places this bedtends to split into an upper gritty limestone with Rhaxella spiculesand a lower sandstone (6 ins.) with fucoids. . .. 2 ft. 3 ins. to 2 6

Trigonia densicostata Lopha gregareaGervillia aviculoides Xysterella muricataGryphaea dilatata Rhynchonelloidea thurmanni

10. Thick bed of blue gritty limestone, sandy and fucoidal at the topand base with Rhaxella spicules in the fucoids .. 2 ft. 3 ins. to 2 9

Pleuromya uniformis Lopha T genufiectaTrigonia densicostata Gryphaea dilatataGervillia aviculoides Rhynchonelloidea thurmanni

9. Hard gritty blue limestone with sandy base and uneven sandy topwhich tends to merge into the base of the bed above 1 0

Holcospongia floriceps .. Terebratula" fileyensisCorynella chadwicki .. Terebratula " sp.Bastinia aspera Paracidaris florigemmaMillericrinus echinatus (Young forms)Pentacrinus sp, Acrosalenia decorataRhynchonelloidea thurmanni Holectypus sp.

244 VERNON WILSON

6

84

1 01 0

8. Hard sandybed, light coloured and nodular in the upper part; a bluegritty limestonewith Rhaxella spiculesin the lower part 1 ft. 6 ins. to 1 9

Gervillia aviculoides Rhynchonelloidea thurmanniLopha gregarea .. Terebratula " fileyensisMillericrinus echinatus .. Terebratula" sp.Pseudodiadema versipora Holcospongia fioricepsNuc/eo/ites scutatus Holcospongia sp,

and fragmentsofcordate ammonites7. Soft grey-brown shelly dirt band ••

Gervil/ia aviculoides Nuc/eolites scutatusAstarte ovata Holcospongia floricepsRhynchonelloidea thurmanni

6. Hard grey, gritty limestone with irregular top and base; shelldebris and detritus in the lower part 1 3

Cardioceras costicardia Acrosalenia decorataLopha gregarea Nucleolites scutatusLopha ?.genuflecta Millericrinus echinatusGervillia aviculoides Holcospongia fioricepsRhynchonelloidea thurmanni Rhaxel/a perforata (spicules)" Terebratula " fileyensis

5. Variable, hard, grey-brown current bedded sandy dirt bed,occupyingthe space between the irregular top of the bed below andthe irregular base of the bed above .. 1 ft. to 1 3

Limatula elliptica Rhynchonelloidea thurmanniCtenostreon proboscideum Serpula tricarinataGryphaea dilatata and fragments of cordateLopha'l genuflecta ammonites

4. Grey sandy limestone, irregular top and base3. Variable consolidated detrital dirt band2. Grey gritty bed with irregular top and base1. Grey gritty bed with irregular top and baseFossils from beds 1, 2, 3 and 4 include :-

Cardioceras costicardia Rhynchonel!oidea thurmanniGryphaea dilatata Pseudomelania heddingtonensisLopha gregarea Littorina muricataLopha genuflecta Littorina muricata var. muricatulaChlamys splendens Nuc/eolites scutatusGervil/ia aviculoides Pseudodiadema versiporaCamptonectes lens Acrosalenia decorataTrigonia densicostata Plates of AstropectenAstarte extensa and Serpuia intestinalis

Chlamysfibrosa, Exogyra nana and one or more species of Serpulaoccur in every bed in the above section.

LOWER CALCAREOUS GRITC. The" Ball Beds." Soft brown sandstone with occasional large

limestone doggers, Exogyra nana, Serpulae and nests of Holco-spongia floriceps are common. . 2 0Soft sandstone with a I-foot band of rounded limestone doggers3 feet from the top of the bed 10 0Soft sandstone with sporadic limestone doggers throughout thebed and a layer of them at the base 3 3The above beds have yielded the following fossils :-

Chlamys fibrosa Trigonia triquetraLima rigida Rhynchonelloidea thurmanniLopha solitaria Collyrites bicordatusPinna lanceolata Serpu/ae

PROC. GEOL. Assoc ., VOL. 60 (1949). Pl.ATE 9

S ECTI ON ON NO RT H SIDE OF FILEY CARR N A Z E.

[To fa a p, 244

3 0

245

3 04101 3

10 03 0

12 0

CORALLIAN ROCKS OF YORKSHIRE COAST

B. Hard grey cherty bed largely composed of the spicules of Rhaxe/laperforata ..

Exogyra nana Gryphaea dilatataChlamys fibrosa Serpu/ae

{

Hard brown sandstone with Rhaxe/la spicules .. . .Three irregular beds of blue-centred gritstone .. . .Hard irregular bed of pale greystone . . . . . .

A. Hard brown gritstone with an occasional limestone doggerHard light blue limestone bed . . . . . . . .Brown gritstones, seen down to low tide mark to ..

Fossils from the above beds A include :-Homomya vezelayi Placunopsis radiataModiola bipartus Trigonia triquetraMytilus ungulatus Rhynchone/loidea thurmanniCh/amys fibrosa Hibo/ites hastatusGryphaea dilatata and Serpu/aeLucina /irata

In the above section Beds 1 to 24 inclusive represent the attenuatedHambleton Oolite Series at this locality. They were regarded asbeing of this age by Hudleston [24] and were included in the" Lower

.Q" . Do . •

o. . O'

o . O' • •

• BOULDER C.(.AY .• D •.". ,

<J' • uo' . 0 <> •

FIG. 42.-DIAGRAM SHOWING 1HB WASHOUT IN 1HB TOP OF THE MIDDLECALCAREOUS GRIT ON 1HB SOUTH SIDE OF FILEY CARR NAZE.

Calcareous Series" of Blake and Hudleston [12, pp. 318-19].Fox-Strangways [19 pp. 315-16], however, regarded all the bedsbetween the Lower Calcareous Grit and the Middle CalcareousGrit (i.e., the Filey Brigg Grit) as belonging to the " Passage Beds"which the Survey [19] recognised as a separate sub-division betweenthe Lower Calcareous Grit and their "Lower Limestone" sub­division or Hambleton Oolites; and he maintained that beds ofthe latter sub-division were unrepresented at Filey. On the faunalevidence these beds are of Hambleton Oolite age, and the Survey's" Passage Beds" are no longer justifiable as a sub-division of theYorkshire Corallian sequence.

Of the beds above the Hambleton Oolite, beds 26 to 34 areexposed along the south side of the Carr Naze and dip southwardbeneath the sea at about 8°. The path leading along the foot ofthe cliff to the Brigg passes over Bed 28, and about 230 yards westof the kiosk at the eastern end of the boulder clay cliffs there occursa remarkable washout in the top of the Middle Calcareous Grit(Bed 31). It is close to the steps leading up the cliff face at thispoint and is some 36 feet long and 2 feet deep (Fig. 42).

246 VERNON WILSON

This washout shows current bedding on a small scale and it iscomposed of rough mis-shaped ooliths and comminuted shellymaterial with eroded micromorphic gastropods. The comminutionpoints to surf action and the current bedding shows that the materialwas washed into the channel fairly rapidly.

The Middle Calcareous Grit is dominated by the massive,poorly fossiliferous sandstone near the base, and the higher beds,though not so lithologically varied as the Hambleton Oolite bedsbelow, frequently contain highly fossiliferous lenses, or thin bandsof grey limestone, shell debris and oolite. The massive sandstonesof the Middle Calcareous Grit form the greater part of the wave­swept Brigg which, on its south side, is largely covered with dislodgedblocks of these rocks. They give.rise to a short cliff on the northside and the underlying Hambleton Oolite beds occupy a narrowerbelt below; they weather out as a series of successive narrow plat­forms. The north-western part of the Brigg is occupied by the upperbeds of the Lower Calcareous Grit ; the soft sandy " Ball Beds"weather easily and give rise to wide platforms on the surface ofwhich the more resistant calcareous doggers stand out prominently.

The distribution of the sub-divisions of the sequence on theCarr Naze and Brigg is shown in Fig. 41. The present Brigg is onlythe worn remnant of a former, more massive structure and withinhistoric times large mounds of boulder clay contributed to itsspectacular character-these have long since been washed away.The faunal elements of the whole sequence from the top of theLower Calcareous Grit up to the disturbed basal beds of the Osming­ton Oolites present many peculiarities. There are heavy, thick­shelled forms of some species and thin-shelled dwarfs of others,while the general character of the fauna as a whole indicates a veryshallow water environment. The dwarfing of many of the formsmay be the result of low salinity of the water. Throughout thesebeds there is a striking abundance of tube-building polychaeteworms-Serpula intestinalis, S. lacerata, S. tricarinata and S.squamosa-which were probably inhabitants of an intertidal zone,their tubes serving as protection and preventing desiccation.

Among the mollusca, Trigonia triquetra, Gryphaea dilatata andCtenostreon proboscideum are present as large thick-shelled forms.Multitudes of Exogyra nana occur in every bed and also encrustinglarger fossils; Lopha gregarea is another common oyster. Burrow­ing forms like Modiola bipartitus and Gervillia aviculoides are alsoconspicuous ; the latter shows a gradual increase in size from thelower beds upwards until it becomes var. megalomorpha in the bedsabove the Filey Brigg Grit. This gradual increase in size probablyindicates a steady increase in the lime concentration of the wateruntil the conditions became ideal for its maximum development.

Species of Chlamys, Lima, Astarte and Lucina are not commonand when present are often small and thin-shelled, and frequently

CORALLIAN ROCKS OF YORKSffiRE COAST 247

fragmentary or broken. While the thick-shelled lamellibranchswere able to endure the severe conditions of a very shallow near­shore environment the thinner-shelled forms were easily destroyed.

The small brachiopods Rhynchonelloidea thurmanni and" Terebratula " fileyensis are abundant and fairly stout; and judgingby the relative size of its foramen the latter form was probablyanchored by a thick, strong pedicle.

Gastropods are rare in the lower beds although such boringforms as Natica might have been expected in some of the sandybeds; however Pseudomelania heddingtonensis begins to appearin the beds above the Filey Brigg Grit and small, eroded micro­morphic forms are abundant in the wash-out in the top of thesebeds on the south side of the Carr Naze.

The occurrence of numerous ossicles of Astropecten and manyfragments of the short-stemmed crinoid Millericrinus echinatus alsopoint to shallow waters, while the little forms of Paracidaris fiori­gemma found the sandy bottom not inimical during these earlytimes though in its larger mature state it evidently favoured themore limy waters of the later Osmington Oolite episode. Flatforms like Pygurus pentagonalis and the starfishes would be betteradapted to a rough environment than taller forms.

Along the coast northward from Filey Brigg the Corallianrocks gradually rise up from the sea floor into the high precipitouscliffs extending as far as Gristhorpe Bay. They form the verticalfaces of the upper part of these cliffs which are unfortunately un­approachable for detailed examination; it can be said, however,that the Hambleton Oolites persist at the top of the cliffs as far asthe small bay known as the" Wyke," some 4400yards north of theBrigg ; here they pass inland and are lost beneath thick drifts.

West of the Wyke the massive yellow beds of the Lower Cal­careous Grit form the vertical upper part of Gristhorpe Cliff withthe thick Oxford Clay forming a steep unstable slope below; andabove it a variable thickness of boulder clay forms an equallytreacherous surface. At Mell-Casty Hill, about 1500 yards westof the Wyke the Lower Calcareous Grit reaches the summit of thecliffs and its outcrop thereafter passes inland beneath the drift,leaving the Oxford Clay to form the constantly foundering cliffsas far as Yons Nab, some 800 yards farther north-westward.

On the west side of Yons Nab the Red Cliff Fault throws downthe lower part of the Lower Calcareous Grit to the west so that itforms the uppermost part of High Red Cliff overlying the OxfordClay and extending westward for a distance of 600 yards. Hereagain the Grit is unfortunately inaccessible for detailed examination.This is the last appearance of the Corallian beds along the coastuntil the Scarborough Castle promontory is reached about 3!miles farther north. Here, a mass of Lower Corallian beds isdown-faulted to the east and has given rise to an impressiveeminence

248 VERNON WILSON

on which the Castle now stands. On the north side of the CastleHill these beds are well exposed and the details of the sequence areas follows:-

5 0

ft. ins.

4 0I 3

1042

5 62

4 62

3 02

2 6

SECfION ON THE NORTH SIDE OF SCARBOROUGH CASTLE HILLHAMBLETON OOLITE SERIES

Oolitic LimestonesIS . Current-bedded detrital oolites with fine shell debris disseminated

throughout and also collected in lenticles and streaks. Purer oolitesabove "

14. Soft oolitic clay parting13. Hard oolitic limestone with comminuted detritus ..12. Soft oolitic parting ..11. Two hard beds of oolite10. Soft oolitic brash-parting9. Prominent hard limestone bed

The fossils from the above beds 9 to 15 include :-Exogyra nana Pseudome/ania heddingtonensisChlamys fibrosa Nuc/eo/ites scutatusOxytoma expansa Holectypus depressaGervillia aviculoides Cidaris smithi (spines)Chlamys splendens Pentacrinus sp,Meleagrinella ova/is Pygurus pentagonalisTrigonia sp, Rhabdophyllia phi//ipsiCylindrites elongatus Holcospongia ftoricepsP/eurotomaria munsteri Serpulae

The Gervi/lia Beds8. Two beds of hard detrital oolite separated by a line of soft brash7. Soft oolite, becoming marly towards the base6. Detrital oolite, the upper 6 inches standing out as a hard band ..5. Thick bed of oolite with much detrital material ..4. Variable parting of red clay with ooliths ..3. Thick beds of detrital oolite, the lowest bed having a very irregular

baseThe predominant fossils in beds 3 to 8 include :-

Gervi/lia aviculoides Rhabdophyllia phillipsiChlamys fibrosa Nucleolites scutatusChlamys sp/endens Holectypus depressaExogyra nana Cidaris smithiPleuromya uniformis Mi//ericrinus echinatusLima rigida Pentacrinus sp.Meleagrine//a ova/is Pseudome/ania heddingtonensisSowerbya triangularis P/eurotomaria munster;Lopha gregarea Cylindrites e/ongatusAstarte ovata Rhynchonelloidea thurmanniPholadomya aequalis .. Terebratu/a .. fileyenslsProeconia rhomboidalis .. Terebratula " sp,Astarte subdepressa Holcospongia floricepsOxytoma expansa Serpu/aeTrigonia sp. (small perIate form)

The Yellow Grits2. Coarse, yellow to grey, gritty limestones containing much fine shelly

material and sand, with softer, more ferruginous sandy partingsbecoming more numerous towards the base .• 10 0

Goniomya literata Gervillia aviculoidesExogyra nana Xystere//a muricata

CORALLIAN ROCKS OF YORKSHIRE COAST 249

Gresslya peregrina Nucleolites scutatusGryphaea dilatata Millericrinus echinatusLopha'l genujlecta Rhynchonelloidea thurmanniChlamys fibrosa Serpulae, and fragments ofLimatula corallina cordate ammonitesLima rigida

1. Irregular, hard and soft, yellow ferruginous sandstones with somedisseminated detrital material and sporadic mis-shaped ooliths.Fossils present include those found in Bed 2 above along withModiola pulchra and Pinna lanceolata 5 6

LOWER CALCAREOUS GRITC. Thick mass of sand containing large rounded limestone doggers.

The .. Ball Beds" .. 14 0Protocardia intertexta Pleuromya uniformisLima rigida Pleuromya alduiniChlamys fibrosa Trigonia triquetraAstarte ovata Lucina lirataGoniomya literata Rhynchonelloidea thurmanniModiola bipartitus and ammonite fragmentsPinna lanceolata

B. Hard cherty sandstone, rather sandy towards the base. Spiculesof Rhaxella perforata common 3 6

A. Thickly bedded buff gritstones in beds from 11 to 3 feet thick .. 49 0Pholadomya hemicardia Inoceramus nitescensArcomya rathieri Cercomya undulataGoniomya iiterata Gressiya peregrinaGoniomya sulcata Pleuromya alduiniPinna lanceolata Lucina lirataNucula oxford/ana Nucleolites scutatusModiola bipartitus Collyrites bicordatusThracia depressa Rhynchonelloidea thurmanniTrigonia triquetra Belemnite fragments and SerpulaePteroperna polydon

In this section the Hambleton Oolite beds show an increase inthickness over the equivalent beds in the Filey section, and therelatively unfossiliferous oolites so characteristic of this series fartherwest are well developed in the upper part of the section. Thefaunal characteristics and shallow water nature of the "YellowGrits" and "Gervillia Beds" are also reminiscent of the lowerpart of the Hambleton Oolites at Filey.

(b) The Hackness HillsAt the eastern end of the Tabular Hills-the main area of the

Corallian formation north of the Vale of Pickering-are the Hack­ness Hills, an outlier separated from the main area to the west andsouth by the River Derwent (Fig. 40). This area is dissected bynumerous small streams and dry valleys which fan out from Hack­ness in all directions to the west, north and east with the result thatthe Corallian beds form a series of smaller outliers. On the dis­sected high ground are the hamlets of Suffield, Silpho and Broxa,with Hackness occupying the low lying central position on theHackness Rock.

250 VERNON WILSON

The Lower Calcareous Grit is best seen in the deep ravine at thehead of Highdales Beck on Hackness Moor some 2750 yards north­west of Silpho, where the section is as follows :-

ft. ins.3. Soft friable calcareous sandstone, weathering and breaking into

small cubical fragments . . . . . . . . . . .. 15 02. Thick massive beds of calcareous sandstone . . . . . . 7 01. Alternating hard and soft beds of calcareous sandstone, with an

occasional wet argillaceous bed, passing down through clayeysandstones to the Oxford Clay below . . . . . . .. 65 0

Rhynchonelloidea thurmanni, Chlamys fibrosa, Exogyra nana,spicules of Rhaxe/la perforata and poor casts of cordateammonites are common in all these beds

The above fossils are also prevalent in the 15 feet of calcareoussandstones seen in a small quarry at Reasty Hill, farther north onthe edge of the Lower Calcareous Grit escarpment. A good sectionof some 20 to 25 feet of thickly bedded calcareous sandstones withintervening softer bands is seen in the roadside pit at the foot ofInn Moor, 1100 yards north-north-east of Suffield and about 17feet of similar beds occur in a quarry on Scalby Nab, 950 yardssouth-east of Suffield. The fossils mentioned above are commonin both these sections together with Isognomon quadrata, Modiolabipartitus, Gervillia aviculoides (small form), Trigonia triquetra andSerpula.

The lower beds of the Hambleton Oolites, formerly known asthe Passage Beds, have been quarried in numerous places and usedfor dry-walling. They are thinly bedded, brown, impure grittylimestones with thin reddish brown clay partings along the beddingplanes ; often many of the beds contain a considerable amount ofcomminuted shelly material embodied mainly in the upper parts ofthe beds. Six feet of the beds occur in the small quarry (11J)on the east side of Merricks Rigg where Gryphaea dilatata, Exogyranana, Chlamys fibrosa, Trigonia triquetra, Pentacrinus sp. andSerpula were recorded. Seven feet of similar beds are also seen inthe quarry (10) south-east of Thirlsey. In the large quarry at thesouth end of Merricks Rigg (19) the basal beds are 13 feet thick;they are more thickly bedded, darker and sandy with clay alongmost of the bedding planes and ground shelly material in the upperparts of some of the beds. Similar beds, 4t feet and 15 feet thickrespectively, are seen in the old quarry (9) north-east of Thirlseyand in the quarry (3) on Hackness Head; in the latter section theupper 6 to 7 feet contain two strong 3 to 4 inch seams of reddishbrown clay. A little farther west of the last exposure three similarclay partings occur in the 15 feet of brown calcareous sandstonesvisible in quarry (4), two occur in the top 4 feet and the third partingis 4t feet from the base of the section.

Overlying these basal impure sandstones and limestones with a

I Figures in parentheses refer to quarry numbers on Fig. 43.

FIo. 43.-THIl OUTCROP OF THE HAMBLETON OoLITE CoRAL-SPONOE REEF IN THE HACKNESS HILLS

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252 VERNON WILSON

very irregular contact is the Hambleton Oolite Coral Reef-aheterogeneous mass of lenses of compound corals, branching corals,calcareous sponges, large numbers of terebratulids and a host ofother fossils-reaching a maximum observed thickness of 11 feet.This reef horizon has been mapped (Fig. 43); at the surface it givesrise to a characteristic type of rough stony clay land full of brokencoral, sponge colonies and other fossils found extensivelyaround thehamlet of Broxa and south-east and south of Suffield. In the out­liers north of Hackness it has a wide dissected outcrop to the northof Silpho and eastward towards Suffield but along the steep flanksof the ravines the outcrop is very narrow.

It is well exposed in a small quarry (1) on the east side of Hack­ness Head where the following details were made out :-

ft. ins.5. Coral-sponge reef-lenses and .. roundheads " of compound coral

with many sponges, terebratulids and other fossils in a matrixof soft buff mud . . 8 0

4. Three beds of soft brown sandy limestone with clay partings alongthe bedding planes. The bottom bed has a very irregular base .. 2 3

3. Variable red clay parting . . 42. Soft .argillaceous sandy limestone . . . . 101. Thick brown calcareous sandstones with irregular ooliths and fine

shell debris . . 10 0

A few yards to the south-west of this quarry is another section(3) where the reef is 11 feet thick and rests unevenly on 15 feet ofbrown granular calcareous grits with intervening thin partings ofred clay in the upper part.

There are no exposures of the reef in the vicinity of Broxa orin its outcrop round the Silpho outlier. An old pit (8) north-eastof Silpho is now almost completely overgrown. Another oldquarry (18) at the south end of the Flock Leys outlier shows only4 feet of the reef on 5 feet on calcareous sandstones, while in thequarry (9) 250 yards north-east of Thirlsey the reef is 3 feet thick witha 2 inch parting of black clay separating it from 4t feet of under­lying impure calcareous sandstones.

In a section (19) near the south end of Merricks Rigg the unevenupper limit of the reef is seen with small patches of the overlyingoolite occupying the shallow depressions of this irregular surface(Fig. 44). Here the reef is only from 6 to 7 feet thick with some13 feet of the usual impure calcareous sandstones below. By far thelargest exposures in this reef occur in the ground to 'the south ofSuffield (12), (13) and (14), where 7 feet of the lower part of the reefrest unevenly on varying thicknesses of the underlying impurecalcareous sandstones.

From all the exposures in the reef mentioned above a largefauna has been obtained :-

Isastraea explanata and Thamnasteria concinna in lenses, colonies andisolated .. roundheads," Thecosmi/ia annularis, Rhabdophyllia phillipsi ;Holcospongiafioriceps , H.polita, H. spp. nov., Peronidella recta, P. sp. nov.,

CORALLIAN ROCKS OF YORKSHIRE COAST 253

Blastinia aspera, Corynella chadwicki, Lopha gregarea, Exogyra nana,Lithophaga inc/usa, Chlamys nattheimensis (small form), Lima zonataand Xysterella muricata comprising the reef fauna, together with Chlamysfibrosa, Camptonectes lens,Pleuromya uniformis, Ctenostreonproboscideum,Astarte ovata, Lima rigida, Proeconia rhomboidalis (small form), Ostreaquadrangularis, Velata anglica, small spines of Cidaris (Plegiocidaris)?smithi, Hemicidaris intermedia, Serpula tricarinata, large numbers of.. Terebratula" fileyensis, .. T." kingsdownensis, Zeilleria hudlestoni,Terebratulina substriata var. suffieldensis and Thecidea sp., and a smallbranched bryozoan.

The highest part of the Hambleton Oolites consists of fairlypure, evenly bedded oolites amounting to 30 feet. Four to fivefeet of these fine white oolites are seen in a quarry (2) on HacknessHead; they are poorly fossiliferous, having yielded only Gervilliaaviculoides, Exogyra nana, Ostrea sp. and Trigonia sp. (cast). These

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FIG. 44.-SECTION IN THE QUARRY NEAR THE SQUIll END OF MERRICKS RIGG,SUFFIELD.

beds are, however, best developed in the large Silpho Quarry (6)south-west of Silpho and two sections near Suffield-the old SuffieldLime Quarry (15) south-west of the village and the second one (16)some 200 yards away to the south-west. In the Silpho Quarrythe section is as follows :-

ft. ins.4 3

3

4 64

12 0

3. Thin bedded shelly limestones with a poor micromorphic fauna ..Xysterella muricata, Exogyra nana, Lopha gregarea, Chlamysfibrosa, Trigonia sp. and Nucleolites scutatus

5. Fine hard white oolite ..4. Variable clay parting . . . . . . . . . . . .3. Fine oolites tending to be split by thin brashy partings along the

bedding planes ..2. Brashy clay band 3 ins. toI. Thickly bedded fine-grained oolite . . . . . . . . . .

Among the fossils recorded from these beds are Chlamys fibrosa,Gervillia aviculoides, Camptonectes lens, Exogyra nana (particularlyabundant in the clayey partings), Pseudomelania heddingtonensis,Nerinaea sp., fragment of a belemnite and a part of a cast of acordate ammonite.

The succession in the large Suffield Lime Quarry (15), disusedfor many years, may still be seen as first described by Blake andHudleston [12, p. 331], and may be summarised as follows :-

ft. ins.4 0

254 VERNON WILSON

ft. ins.2. Thick small-grained oolites with few fossils .. 10 01. Fossiliferous suboolitic limestones with a megalomorphic fauna.

There may be some 6 to 8 feet of beds lying below the floor of thequarry 3 6

Oxytoma expansa, Isognomon quadrata, Gervillia aviculoides andcasts of large ammonites.

In the neighbouring quarry (16) the series consists of marlyoolites with intervening partings of soft brash; the details are asfollows :-

ft. ins.

3 6

39262

112

3 22

2 6

1 in. to

1 in. to

11. Fine grey oolitic limestone with much disseminated detritus; veryshelly in the bottom 6 inches

Exogyra nana, Camptonectes lens, Lopha gregarea and Gervilliaaviculoides

to. Clayey brash9. Oolite with Chlamys fibrosa, Exogyra nana8. Brash parting7. Thin bed of oolite with Exogyra nana6. Parting of clay and brash5. Oolite4. Clay parting3. Oolite2. Clay parting1. Oolite

In the bottom five beds Exogyra nana, Ch/amys fibrosa, Astarteovata, Gervi//ia avicu/oides, Pseudome/ania heddingtonensis andSerpulae are common, and an occasional cidarid spine is present.In places small patches of dark chert are not infrequent.

Through the absence of exposures little is known about the MiddleCalcareous Grit facies in the Hackness Hills. It is an impure greysandy oolitic limestone, very poor in fossils, and gives rise to a redclayey soil carrying much debris of the rock.

VARIATIONS IN GRAIN SIZE AND THE RANGE ANDDISTRIBUTION OF THE SPICULES OF RHAXELLA PER­

FORATA IllNDEThin sections of many of the beds, particularly from the coast

sections, were prepared in order to determine the extent to which thespicules of the hexactinellid sponge Rhaxella perforata Hinde had:­

(a) contributed to the formation of the Lower CalcareousGrit; and

(b) persisted from Lower Calcareous Grit times and contributedto the building of the later sediments.

The examination of the thin sections has also yielded someinteresting information on the size and character of the detritalconstituents which must now be considered. The calcareousgritstones reveal that :-

(a) the detrital constituents are subordinate to the matrix(b) the detrital quartz is characterised by irregular or no

inclusions.

CORALLIAN ROCKS OF YORKSHIRE COAST 255

Quartz grains with no inclusions are the more abundant, andespecially characterise the more finely grained beds ; it may be thatthe greater abundance of these grains is due to the detrition oflarger grains with irregular inclusions along the lines of theinclusions.

In the Lower Calcareous Grit detrital material is fairly abundant,quartz grains predominate and an occasional fragment of felsparis present. The matrix is essentially calcite with some limoniticand clayey matter; there is also a certain amount of siliceouscement, the distribution of which is very irregular. Many cal­careous sandstones have a rough gritty weathered surface due tothe solution of the cement at the exposed surface; if, in addition,there is also a framework of interstitial siliceous cement this weather­ing effect is still more striking, and it is very characteristic of theweathered surfaces of the Lower Calcareous Grit being often seenin some of the higher beds on the coast.

In the coast sections the quartz grains are angular and up to'2 mm. in size, and they contain irregular inclusions, but in theHackness Hills the grains are much smaller, averaging '1 mm. andless, and inclusions are less frequently visible. In the LowerCalcareous Grits at Scarborough Castle Hill there appears to berather more detrital quartz than elsewhere and many of the grainsare in contact. In the hard band immediately underlying the" Ball Beds" the quartz is mainly subangular though many angulargrains are present and there are occasional rounded individuals;they are not in contact and are in about equal proportion to thecalcite matrix. The coarser character of the allogenic constituentson the coast points to derivation from the east. The fact that thegrains are seldom in contact indicates contemporaneous cementationand continuous crystallisation during deposition.

When seen in thin section the Hambleton Oolite beds at Fileyappear as mainly fine arenaceous shelly limestones with the angularquartz varying in size from coarse medium to fine grained. Someof the more oolitic beds contain considerable quantities of groundshell debris. In the Hackness district the brown ferruginous lime­stones forming the lowest part of the Hambleton Oolite series arelargely composed of this broken shell detritus with about 5 per centof angular quartz. In the oolite above, at Hackness and at Scar­borough Castle Hill, the ooliths vary in size and shape and at thelatter locality they are generally larger; the calcite cement generallyshows very little recrystallisation. Quartz amounts to 5-10 percent of the rock and it is interesting to note that the grains are largerand more abundant than in the equivalent beds farther west towardsNewtondale and Pickering.

In the sandy beds with the anastomosing structures commonlycalled "fucoids" (Plate 10) in the Filey section the rock consistsmainly of fine quartz grains frequently cemented by opaline silica ;

256 VERNON WILSON

the" fucoids" are sharply defined and a section across an individual" fucoid " reveals the outer part as an arenaceous limestone con­taining 20-25 per cent of quartz; towards the centre the amount ofdetrital quartz decreases as the proportion of the spicules of Rhaxellaperforata increases. Similar" fucoids" were described by Blake andHudleston [12, p. 271] in the Sandsfoot Grit on the Dorset coast,and more recently Dr. Arkell [8, p. 63] has said of them, " it is notestablished that the appearances suggestive of fucoids cannot beproduced by concretionary action."

At Filey the massive grits of the Middle Calcareous Grit containabundant quartz in a matrix of calcite and limonite. The quartzis mainly subangular and for the most part the grains are in contact.In the Hackness area arenaceous limestones of Middle CalcareousGrit age contain subangular quartz grains with irregular inclusionsin a calcite cementing medium, which has undergone slightrecrystaIlisation, containing a high proportion of limonite.

In 1851, Sorby noticed certain reniform bodies preserved inagate together with small cellular bodies and sponge spiculesin theLower Calcareous Grit of the Yorkshire coast [38] ; he estimatedthat there were about 21 millions of these bodies in a cubic inch ofthe rock and " I shall not be overrating them if I suppose them toconstitute 20 per cent of the whole rock." In 1890Hinde confirmedthe presence of these globate bodies in this rock and consideredthem to be the spicules of a new hexactineIlid sponge which henamed Rhaxella, and described the species Rhaxella perforata[22] ; in a later monograph he enlarged on this description. Sincethen calcareous and siliceous forms of the spicules have beenrecognised and described by Dr. A. Morley Davies [16] from theArngrove Stone, where he has also recognised several variations inthe preservation of the siliceous forms. The writer has also des­cribed several variations in the mode of preservation of the spiculesin the Lower Calcareous Grit in the Howardian Hills in Yorkshire[45].

The spicules have their greatest distribution in the Lower Cal­careous Grit throughout Yorkshire to such an extent in somelocalities as to form massive beds of light grey blue chert entirelycomposed of siliceous forms. In the coast sections siliceous andcalcareous forms are disseminated throughout the lower, mainpart of the Lower Calcareous Grit, with the calcareous forms pre­dominating in the blue limestone centred parts of these beds. Thelarge doggers in the "Ball Beds" contain a high proportion ofcalcareous spicules intermixed with fine shell debris ; spicules areabsent from the sandy part of these beds.

In the Hambleton Oolite Series, calcareous spicules are locallyabundant at Filey, and are rare in the equivalent beds at Scar­borough Castle Hill. Occasional calcareous forms occur in thebasal impure calcareous gritstones beneath the Hambleton Oolite

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CORALLIAN ROCKS OF YORKSHIRE COAST 257

Coral Rag in the Hackness area. The highest oolites of this seriesare devoid of these spicules.

Calcareous and siliceous forms are common in many of the morecalcareous gritstone beds in the Middle Calcareous Grit at Filey.

THE PALAEOECOLOGY OF THE HAMBLETON OOLITEREEF AND ASSOCIATED SEDUWENTS

The remarkable faunal association of corals, calcareous sponges,terebratulids and their associated molluscan fauna in the HambletonOolite of the Hackness Hills can only be ascribed to the palaeoeco­logical relations of the time, to understand which it will be necessaryto see what guidance can be obtained from our incomplete know­ledge of the ecology of the descendants of the fossil groups livingin modern marine environments.

Twenhofel [41] has pointed out that "every organism liveswhere it does because the combined impact of all the environmentalconditions permits it to live there. Animals in the sea organisethemselves into communities of which the individuals are adaptedto each other so that each constitutes a definite cog in the economyof the association." Agassiz [1, p. 10] observed how remarkableit was that the littoral fauna changes with the constitution of thebottom. What then were the environmental factors which allowedthe calcareous sponges and terebratulids to form a reef communitywith corals in lower Hambleton Oolite times, an association whichnever again arose in subsequent Corallian episodes in Britain?

The great majority of the modern calcareous sponges occur inrelatively shallow water from the tidal zone down to 30 fathoms,and nearly all of them live under conditions of good illuminationin clear water free from mud, and according to Oakley [27, p. 335]they are often associated with sandy sea floors. They are sessileand incapable of locomotion in the adult state. In a recent studyof the ecology of the porifera, de Laubenfels [17] points out thatsponges living

amid rapid currents always lack pronounced surface elevations. Thestronger the current the more nearly level will be the surface of the sponge.Where the currents are very violent indeed, the rule is that the sponges takewhat is called the encrusting form, extending laterally indefinitely, but neverprotruding far above the substratum and growing in a hemisphaerical orlow rounded manner that is very characteristic.

Thus calcareous sponges living on the sandy and current-sweptfloors of warm shallow littoral seas are less regular and symmetricalthan those of deeper water habitat and they usually encrust rocks,shells and other organisms or rest directly on the sea floor, underwhich conditions they reach their greatest abundance. de Lauben­fels [17] concludes :-

What little evidence is available from references to polyphyletic fossilfaunas bears out the theory that the ages have witnessed little change in

258 VERNON WILSON

the methods whereby sponges react to their environments. It appears thatin the past Porifera occurred in much the same environments as at present,and lived similar lives.

The first calcareous sponges invaded this area towards the close ofLower Calcareous Grit times but it was not until some time laterthat the Hackness reef was established. Their remains are firstfound in the top two feet of the Lower Calcareous Grit at Filey andwhile they persisted into higher beds in this area they were alsomigrating north-westward towards the Scarborough district, wherethey are first found in the lower Hambleton Oolite beds. A littlelater they congregated in a greater profusion of numbers and speciesunder evidently more congenial conditions in the neighbourhoodof Hackness. The fact that they are small rounded individuals orbranching colonies without elevated oscula or other projectionsand many of the individuals, particularly Holcospongia polita,encrust other fossils, points to their living in shallow waters whichwere agitated and current-swept and in which little deposition wastaking place. The relative numbers of the various species in acollection of over 300 specimens from the Hackness district are asfollows :-

Holcospongia politaHolcospongia fioricepsCorynella chadwickiPeronidella recta

214 specimens63264

It is interesting to note that among the collections made by theChallenger and other dredging operations, the stations whichyielded no calcareous sponges were consistently far from land andno stations which were a great distance from the nearest landyielded many sponges. It may be inferred that wherever fossilcalcareous sponges are abundant in deposits of shallow waterorigin there was probably a land area not far away.

In their work on the Inferior Oolite sponges-mainly calcareous-from Gloucestershire, Richardson and Thacker [31, p. 163]conclude that " the rocks in which they were found were formed inshallow marine waters, probably near a coast," probably the marginof the old Welsh geanticlinalland mass.

The present ecological distribution of brachiopods appears tobe in harmony with their distribution in the past, excepting therhynchonellids, of which the fossil forms had great developmentand distribution in shallow waters in bygone periods. On thissubject Cooper [15] makes the following points :-

(i) 60 per cent of living brachiopods species occupy shallowwater but only little more than half this percentage isactually confined to shallow water.

(ii) Terebratulids are the most abundant group living today,forming rather less than 70 per cent of the known generaand are mostly confined to shallow waters.

CORALLIAN ROCKS OF YORKSffiRE COAST 259

(iii) Reefs are ideal habitats for brachiopods because thewaters are warm, aerated and well lighted; and coralsassociated with brachiopods in very fine muds point toshallow water.

He concludes that" except for bizarre types and unusual formsthere is nothing to indicate that the brachiopods lived in the past ina manner different from that followed today."

Schuchert [33] had earlier expressed similar views that"brachiopods when large, thick shelled and abundant clearlyindicate to the palaeontologist animals inhabiting very shallowwaters of probably less depth than 100 feet. Further that thesewaters were in close proximity to the shores and probably werewarm."

The occurrence of the robust globate terebratulids in suchprofusion in the Hackness reef and their presence with Rhyn­chonelloidea thurmanni in about equal numbers in the lower Hamble­ton Oolite beds at Scarborough and Filey further supports the viewthat these deposits were formed near land and in shallow water.

In recent years the detailed investigations by Dr. W. J. Arkell[2, 4, and 5] of the Corallian reefs in the Midlands have led him tothe belief that while they were formed under conditions similar tomodern reefs they grew at depths much shallower than 120 feet andin fact they " were formed at times when the sea-bed was all butnearest the surface of the sea and was still rising." He has furtherdrawn attention to the small number of constituent species in ourCorallian reefs compared with modern reefs, also pointing out that"the farther south we trace the Corallian beds and other oolitesin Europe, the richer they become in reefs and the richer the reefsbecome in species, until in the region of the Jura Mountains wereach the metropolis of coral growth in Jurassic times" [5, p. 193].In addition to being the metropolis of coral reef development thissouth-central European area was also the centre of the developmentof huge sponge reefs together with many other faunal associationson a grand scale both as regards numbers and species.

In the light of the above statements, attention may be drawnhere to the virtual absence of calcareous sponges and terebratulidsin the main episode of coral reef development in the Upper Corallianin this country; their absence is the more unaccountable when it isremembered how they became established in considerable strengthas reef builders along with the corals in lower Hambleton Oolitetimes in Yorkshire. It may be that the local conditions which weresuitable for the association of sponges and corals in the earlierepisode were not exactly repeated in later Corallian times.

Chemical precipitation of calcareous muds occurs at the end ofthe sedimentary cycle, clay-sand-limestone, when presumablythe lime concentration is at its highest; and, provided localenvironmental conditions are suitable, reef formation frequently

260 VERNON WILSON

develops towards the end of the limestone facies and is associatedwith a profuse molluscan fauna, rich in species and individuals, allforms reaching a maximum size and attaining a maximum thicknessof shell. A low salinity or any reduction in the salinity has anadverse effect and results in an impoverished fauna, poor in speciesand dwarfed in size though often rich in individuals, and along withthe dwarfing of species goes a decrease in thickness of shell. Amongeuryhaline' animals, individuals living in reduced salinities fre­quently have a smaller maximum size than do those of the samespecies inhabitating more saline waters [39, pp. 840-2]. Corals aretolerant to a 20 per cent reduction in the salinity of the water oftheir normal environment.

According to the same authors [39, pp. 997-1004] there is atendency for the calcium carbonate content of sediments to increaseaway from the coast, and in modern seas and sea bottoms thetransition from sediments low in carbonate to those higher in cal­careous material usually occurs within a relatively short distance.That this was true in Hambleton Oolite times is evident from thepresence of shallow water largely arenaceous, sediments in the vicin­ity of Filey while at Hackness, a few miles away, a rich reef wasimmediately followed by pure oolites. It would appear then that,all other factors being favourable, the salinity and degree of limeconcentration governed the rise and development of this uniqueHambleton Oolite reef association; and, in summing up, thefollowing points are made :-

(1) Calcareous sponges thrive along with corals in waters ofonly just sufficient lime concentration for the active growthand metabolism of the reef building corals, but do notflourish in waters with a high degree of lime concentration.Even the corals are impoverished in so far as the compoundforms do not develop into the huge massive colonies oflater episodes but occur only as restricted lenses within themain reef mass.

(2) The local profusion of terebratulids was also achieved inwaters of not too high lime concentration; this is alsosupported by their presence in the equivalent sandy lime­stones at Filey and Scarborough where conditions wereeven less calcareous than in the vicinity of Hackness.

(3) That the lime concentration of the water was not as highas it was during the formation of oolitic limestone mudsis evident from the immature nature of some of the otherelements of the associated fauna of this reef. Many ofthe species are small and thin shelled and few attain theusual size as found in the later Osmington Oolite episode,e.g., Chlamys nattheimensis and Proeconia rhomboidalisare both small.

I .. Euryhaline animals are those having a great degree of tolerance to wide ranges of salinity;they are naturally characteristic inhabitants of coastal regions and estuaries. The degree .,feurybalinity varies greatly in different species" [39, pp. 840-2].

CORALLIAN ROCKS OF YORKSHIRE COAST 261

The Upper Corallian coral reefs grew at the end of a phase ofcalcium carbonate deposition ; they were profuse in coral speciesand in the numbers and species of the associated molluscan fauna,but in this area the lower Hambleton Oolite coral-sponge reef grewrelatively soon after the end of the sandy conditions of the LowerCalcareous Grit without any intervening deposition of limestone.

GEOLOGICAL mSTORY OF THE AREA(a) Conditions of Sedimentation

Towards the close of the Oxford Clay episode the conditions ofclay deposition began to be modified by the influx of fine arenaceousdetritus. At first the change was gradual but as the quantity ofsediment increased the dark muddy conditions were eventuallyreplaced by clearer waters in which accumulated the calcareousgritstones of the Lower Calcareous Grit.

The influx of sandy material remained constant and uniformduring the whole of this succeeding episode; the material wasevenly distributed over the sea floor and a considerable thicknesswas laid down. Throughout this time vast numbers of the siliceoussponge Rhaxella perforata inhabited the sea and as they died anddecayed their skeletal elements in the form of tiny globate spiculessettled in myriads on the sea bed, where they formed a considerablepart of the accumulating deposit.

At the end of Lower Calcareous Grit times the sea was shallowand the influx of material began to slacken on account of the generalrelief of the land supplying this detritus having been steadilyreduced over a long period of time.

As the shallowing proceeded the sea floor came under theinfluence of wave and current action, and the critical point ofdeposition and erosion was reached where the sediments were onlytemporarily deposited and local non-sequences resulted. Whensea level remained stationary for a time a base level of depositionwas reached with the cessation of any further deposition until theconditions changed and a new base level was produced above theoriginal one. These influences were more pronounced in theshallowest parts nearest to land. The gritty limestones and cal­careous gritstones of the Hambleton Oolite Series--especially thelowest beds of the series-at Filey show abundant evidence of veryvariable shallow water conditions during these times.

The gradual reduction in the general elevation of the neigh­bouring land was reflected in the slow diminution of the quantityof detritus carried to the sea and correspondingly the lime concen­tration of the water slowly increased. Early evidence of theincrease is provided by the tangled knots of serpulid tubes and theincoming of sporadic colonies of calcareous sponges-bothindications of shallow water-in the top bed (Bed C) of the LowerCalcareous Grit at Filey.

262 VERNON WILSON

In the Filey district conditions rapidly became extremely shallow,perhaps even intertidal, in early Hambleton Oolite times. A fewinches of gritty limestone were deposited, cemented and hardened;wave and current action then prevented further deposition for atime, and the irregular, indurated surface of the bed is evidence ofits also having suffered some degree of erosion. The currentswere again modified or the floor sank low enough to be out of theirrange and, after whisps of mud and shell detritus had been washedinto its surface irregularities, another bed of gritty limestone waslaid down. The same process of hardening and scouring by wavesand currents was then repeated. These unstable conditions pre­vailed for a time-represented by Beds 1 to 4-and were followedby similar slow shallow water deposition which, however, was notaccompanied by intermittent erosion of newly formed deposits bystrong currents.

In attempting a possible explanation of the peculiar " fucoid "layers it should be noted that :-

(a) They occur in a condensed sequence of gritty limestones,(b) they adhere to the base of a particular bed and never to

the upper surface, and often two layers of them occur oneimmediately above the other,

(c) they are found only in these beds at Filey and not at Scar­borough or elsewhere in these rocks in Yorkshire.

The end of the deposition of any bed is marked by its upperbedding plane, and the material for the formation of the next bedthen begins to accumulate under normal conditions. If the searecedes after the deposition of the initial layer of-the new bed andit is exposed to the drying action of the air and sun it will developa system of cracks. With the readvance of the tide and theresumption of deposition these cracks will be filled in, and it may bethat the new infilling material contains a higher proportion ofcementing matter, with the result that the infillings are bettercemented than the surrounding sediment which has been cracked.This process may be repeated before the accumulation of the newbed becomes stabilised and continuous and, as in many instances,two sun-cracked layers occur one above the other.

If, as is here premised, these beds at Filey were laid down invery shallow intertidal waters the sun-cracked layers would bedeveloped from time to time, but farther out to sea towards Scar­borough deposition would be continuous.

When subsequently in a later age the sun-cracked layers aresubjected, as at the present time, to weathering action or attack bythe sea the less well cemented sediment would be most easilyremoved and leave the more resistant anastomosing infillings.

It is interesting to note that Dr. J. Bridge [13, p. 122 and Plate15B] has observed and recorded many layers of similar structures

CORALLIAN ROCKS OF YORKSHIRE COAST 263

in the Roubidoux Sandstone of Ordovician age in Missouri, U.S.A.,and he unhesitatingly states that they are the result of infilled suncracks developed in the sandstone during its formation in veryshallow water. I am indebted to Dr. Arkell for bringing to mynotice a paper by Rieth [32] on similar" fucoids" found at fourhorizons in the Jurassic sequence in the Swabian Jura, and whichare considered to be pseudomorphs after branching cylindricaland horn-type sponges. Rieth also thinks they are indicative ofvery shallow water conditions, and probably lived near the shore.

While, in the Filey district, the Hambleton Oolite deposits wereof extremely shallow water and near-shore character, farther to thenorth-west in the vicinity of Scarborough and Hackness theyretained their shallow water character but show no evidence of intra­formational submarine erosion. At Scarborough the lower bedsare detrital and similar in many respects to the equivalent beds atFiley, but the highest beds are thinly bedded detrital oolites­deposited in quieter shallow waters-a facies unrepresented at Filey.

In the Hackness district fine shell detritus and mud were laiddown to a thickness of about 25 feet in the early stages of thisepisode until, perhaps through failure in the supply of the detritusor by reason of a radical change in the sea currents, the conditionswere arrested and replaced by a quiet habitat in which a burst oforganic activity took place. Or it may have been that the seareached a degree of shallowness which, together with the otherrequisite factors, I was favourable to the development of a reef.

In these warm waters corals, sponges, terebratulids and asso­ciated organisms grew and lived in great profusion to form a uniquereef. With the exception of the corals and some of the molluscsmost of the organisms which contributed to and enjoyed the sanctu­ary of the reef had been living, perhaps rather precariously, throughthe early stages of the period in the shallower waters to the south­east of Hackness. This activity was only brought to a close whena further sagging of the sea floor carried the organic structuredown to a depth at which the continued existence of the organismsbecame impossible and further development was abruptly stopped.

The sea was now rich in lime and later deposits laid down onthe reef were pure oolites, at first in fairly thick beds, but becomingmore thinly bedded and flaggy in the upper part. To the south­east in the Scarborough district the oolitic muds were not so pure,having a considerable admixture of shell debris and fine grittysediment, whereas in the vicinity of Filey the corresponding bedshave no oolitic character but were predominantly gritty limestones,with an occasional thin lens of oolite, similar to the underlying beds.

In the succeeding Middle Calcareous Grit episode a greater

I .. Physical factors to which the marine animal must adjust itself include physical characterof the bottom, temperature, depth, marine currents, salinity and amount of light. When anyoneof these factors in the physical environment falls below the minimum requirement of a particularspecies, elimination of that species from the facies results" 126).

264 VERNON WILSON

influx of sandy material took place in the south-east and thick,partly wedge-bedded sandstones were laid down at Filey. Depositsof this age are absent at Scarborough, but to the north-west some ofthe finer sandy detritus was carried from the Filey district to beincorporated with the oolitic muds, the deposition of which stillpersisted in the Hackness Hills in Middle Calcareous Grit times.

(b) PalaeogeographyFrom the work of Dr. Rastall in Yorkshire [4, p. 581J it is in­

ferred that the Dogger and Middle Lias were derived from the Fenno­Scandian land area which probably extended westward over partof the site of the present North Sea.

More recently, Dr. Smithson [37] has studied the grain sizesand distribution of the heavy minerals in the Middle Jurassicdeposits of Yorkshire and he also concludes that they too were inpart derived from a North Sea land area which reached at least asfar south as the latitude o~the Market Weighton axis. He visualises" a narrow land running parallel to the Pennine mass and not farremoved from the present coast line."

Fox-Strangways [19, p. 283] has also drawn attention to the viewof Godwin-Austen who considered that the greater part of the areaof the North Sea was land during the oolitic period.

Again, in North Germany, Brinkman [14] and Schott [34] havethrown some light on the south-west extension of this ancient landmass and the extent to which it supplied sediment to the adjoiningJurassic seas covering that region. From their stratigraphical andpetrological investigations they have shown that "at least fromVesulian to Kimeridgian times the bulk of the clastic sedimentdeposited in the North German sea was derived from the north.Every formation when followed from north to south passes fromsand into clay" [4, p. 597].

In this country and particularly in Yorkshire there is little orno evidence indicating the probable extent of this land area towardsour shores from Cornbrash to Lower Oxfordian times. But, in hisdescription of the Hambleton Oolite and Middle Calcareous Gritbeds at Filey, Hudleston expressed the view that they probablyterminated not far to the south east; and though he did not expressany such thought, he may nevertheless have visualised the existenceof land in that direction at this time. It is now considered, on theevidence discussed in the foregoing account, that there was a westernextension of this eastern land area in Hambleton Oolite and MiddleCalcareous Grit times to within a short distance of our presentshores of Yorkshire. Briefly summarised the evidence is asfollows :-

(a) The gritstones and sandy limestones in the Filey neigh­bourhood pass north-westward into purer calcareous rocks.

(b) The grain size of the detrital quartz in these rocks dimin­ishes in the same direction.

CORALLIAN ROCKS OF YORKSHIRE COAST 265

(c) In the Filey neighbourhood the whole sequence is muchcondensed and there is evidence of repeated introforma­tional erosion in early Hambleton Oolite times. Atintervals, in the higher beds, the sea receded and the thintop layers of the sediments were frequently dried andcracked.

(d) The fauna of these rocks, particularly at Filey, is of inshoreshallow character, and at one stage in the Hackness districta reef flourished in rather less shallow water.

This land area, then, is visualised as being of fairly low reliefand supplying a steadily decreasing amount of sediment to a wide,very shallow fringing sea from the end of Lower Calcareous Grittimes to the end of the Middle Calcareous Grit episode. The waterwas clear and free from mud and was warm enough for the marginalcoral-sponge reef to develop in mid-Hambleton Oolite times.

In the marine zone nearest to the land, at Filey, the sedimentsaccumulated slowly with frequent intervals of non-deposition whenthe material was swept farther out to sea towards Scarboroughand the north-west by offshore currents. There is no evidence toshow that any such currents were at any time very strong or thatthey flowed in any particular direction; the evidence points to auniform scouring of the sea bed having taken place at intervals inthe Filey neighbourhood. Sometimes this scouring action onlyprevented the accumulation of sediment while at other times it wasstrong enough to erode the sea floor.

In Middle Calcareous Grit times an increased quantity of sedi­ment was washed into the Filey area while farther away to the north­west the deposition of limy oolitic muds persisted from the laterstages of the Hambleton Oolite Period with only little admixtureof the finest sediment.

At the end of this episode, either no sediment was being carriedto the sea from the reduced eastern land area, or its shores may havereceded eastward so that the zone of sandy deposition in later timesnever reached the area that is now land in Yorkshire, for in thesucceeding episode quiet limy oolitic muds were widespread overthe whole of the Yorkshire basin.

PALAEONTOLOGICAL NOTES ON THE CALCISPONGlAEMore than 300 specimens of calcareous sponges have been

collected from the various exposures of the Hambleton Oolite reefin the Hackness neighbourhood. They all occur in a matrixof fine mud which has to be removed before they can be studied.Much of this material can be removed from the specimen by re­peated soaking and washing with water, but much of it is em­bedded in the fibrous structure of the sponge and in order to elimin­ate it other methods have to be devised. The use of dilute acids

266 VERNON WILSON

was ruled out because they attacked the sponge structure. Itwas found possible, however, to remove a considerable amountof the interstitial mud by covering the specimens with powderedcaustic potash which, on deliquescing in the atmosphere, drawsout the fine muddy particles. The process is slow and laboriousbut eventually a specimen can be cleaned sufficiently for accuratedetailed examination.

In the cases of forms like Corynella which possess a gastralchamber opening at the upper surface in an osculum the mudfilling this chamber can be largely removed by dental appliances.

The following notes on the recognised species are intendedto supplement the descriptions and notes on these species by Hinde[21], Siemiradzki [35] and Oppliger [28 and 29].Holcospongia polita Hinde

Simple and compound sponges encrusting shells, echinoidspines and slender corals like Rhabdophyl/ia phillipsi. The opencanals which radiate down the sides of the sponge from a depressedosculum on the upper surface are 15 in number; they are quitestraight, of uniform width, and are radially symmetrical around theosculum. Traces of an outer dermal layer are occasionally presentnear the base of the sponge.H. floriceps (Phillips)

Simple obtusely conical or subcylindrical and compoundsponges, the latter being most common. The largest compoundspecimen collected has 10 individuals. They encrust shells, wormtubes and corals. . The open surface furrows are from 6 to 10 innumber, they are coarse and wide and frequently appear to be linedwith a thin dermal layer though usually this has been weatheredaway. In most specimens the summit is truncated and the opencanals are not symmetrically spaced down the sides.

H. polita is distinguished from this species by its greater numberof straight radially symmetrical open surface furrows, and by itsdifference in general form.H. bernensis (Etallon) Plate 11, Figs. 4 a and b.

Two specimens of simple sponges which appear to belong tothis species have been found at Hackness. They are identical withOppliger's [28] Plate 1, Fig. SA. In height they measure 8.5 mm.and 8.7 mm. respectively, and 14.4 mm. and 13.8 mm. respectivelyin breadth. The upper surface is flattened and from a shallowosculum radiate narrow irregular and often bifurcating, opencanals down the sides. The surface canals have no radially sym­metrical distribution. This Swiss species has not previously beenrecorded in England.H. bella Hinde. Plate 11, Fig.2.

One discoid specimen has been found which appears to be

PROC. GEOL. Assoc., VOL. 60 (1949). PLATE 11

6

58b

7

a9

LOWER CORALUAN CALCISPONIAGE FROM N.E. YORKSHIRE.

[To face p, 267.

CORALLIAN ROCKS OF YORKSHIRE COAST 267

identical with this Inferior Oolite species. It is 7.4 mm. in breadthand 3.2 mm. thick with six open grooves radiating from the centreto the margin of the upper surface. The specimen has beenencrusting a corallite of Rhabdophyllia phillipsi,

H. smithi sp. nov. Plate 11, Figs. 5 a and b.Small hemispherical to globular, simple encrusting form. At

the rounded apex is a central trefoil shaped osculum, and aroundare six short deep furrows extending in a symmetrical pattern fromthe rim of the osculum. The furrows do not appear to have anyconnection with the osculum. So far only one specimen of thisspecies has been found; it is 5.8 mm. high and 8 mm. in breadth,and its fibrous structure is open though delicate, resembling that ofH. polita.

H. hindei sp. nov. Plate 11, Figs. I a and b.This undoubtedly new species is a simple spherical form which

appears to have had a stalk of attachment. The whole surface iscut up by wide deep grooves with intervening, sharply angular,irregular ridges. Four of the ridges converge to form a pointedapex; the other ridges end at varying distances from this apex.In plan the specimen has a somewhat stellate appearance (Fig. 1 a) ;it is 9.8 mm. high and 10.2 mm. wide. Only one specimen is so farknown.

H. suffieldensis sp. nov. Plate 11, Figs. 3 a and b.Small, simple, spherical, encrusting forms with rather flattened

upper surface carrying a slightly depressed osculum. From theosculum five canals radiate to varying distances down the sides,the longest canal never extends any farther than about halfway downthe side of the specimen while the shortest canal is little more than awide gap in the margin of the osculum. The spicular structure issimilar to that of H. polita. Of the four specimens collected thelargest measures 11 mm. in height and 9.9 mm. in breadth.

Peronidella recta Hinde. Plate 11, Figs. 6 and 7.Five specimens referred to this species have been found, two of

which are illustrated. Three are single forms varying in lengthfrom 7.6 mm, to 17.8 mm. and from 4.7 mm. to 6.2 mm. in breadth.All, except one, have the pronounced truncated summit character­istic of the species, with the small circular cloacal aperture about1 mm. in diameter.

P. hacknessi sp. nov. Plate 11, Figs. 8 a and b, 9 a and b.Eight single specimens and one colony of two have been collected,

which are spherical and encrusting in their mode of growth. Theirsummits are rounded with small circular cloacal aperture but intwo specimens, one of which is figured (Figs. 9 a and b) this aperturehas an inner trefoil-like form. The outer surface is smooth and thePROC. GEOL. Assoc., VOL. 60, PART 4, 1949. 19

268 VERNON WILSON

spicular structure is similar to that of P. recta, from which thisspecies differs in its spherical form.

Corynella chadwicki HindeThe species exhibits a wide range of size and shape and all the

specimens collected are of simple habit. There are straight andcurved cylindrical forms, others are club-shaped to near sphericaltapering gently to a broad flat summit occupied by a wide osculum.One globose specimen has a nodose swelling about half way downits side with a subsidiary depressed cloacal opening. The marginof the osculum is entire in every specimen with no traces of anyopen furrows radiating from it.

EXPLANATION OF PLATES 9-11PLATE 9

NORTII SIDE OF FILEY CARR NAZE. Section at the entrance to the first doodleshowing lower Hambleton 'Oolite beds and Middle Calcareous Grit overlyingthe "Ball Beds" (Lower Calcareous Grit).

PLATE 10SLAB OF HAMBLETON OOLITE ON FILEY CARR NAZE SHOWING "FUCOIDS."

(published by permission of the Director of the Geological Survey).

PLATE 11LOWER CORALLIAN CALCISPONGIAE FROM N.E. YORKSHIRE.

1 a and b.-Holcospongia hindei sp. nov.2.-H. bella Hinde.3 a and b.-H. suffieldensis sp. nov.4 a and b.-H. bernensis (Etallon).5 a and b.-H. smithi sp. nov.6 and 7.-Peronidella recta Hinde.8 a and band 9 a and b.-P. hacknessi sp, nov.

All the above specimens are in the Author's collection and are here reproducedtwice natural size.

REFERENCES1. AGASSIZ, A. 1888. Three Cruises of the Blake. Mus. Camp. Zool.,

p. 10.2. ARKELL, W. J. 1928. Aspects of the Ecology of Certain Fossil Coral Reefs.

Journ. Ecol., 16, pp. 134-49.3. ---,. 1929-35. British Corallian Lamellibranchiata, Mon. Pal. Soc.4. . 1933. The Jurassic System in Britain. Oxford. Chap. 13,

pp. 420-32 ; chap. 18, pp. 557-67 ; pp. 580-99.5. ---. 1935. On the nature, origin and climatic significance of the

Coral reefs in the vicinity of Oxford. Quart. Journ, Geol. Soc., 91,pp. 77-110.

6. ---. 1935-48. A Monograph on the Ammonites of the EnglishCorallian Beds. Mon. Pal. Soc.

7. . 1936. The Ammonite Zones of the Upper Oxfordian ofOxford, and the Horizons of Sowerbys' and Buckman's Types. Quart.Journ. Geol. Soc., 92, pp. 146-87.

8. ---. 1936. The Corallian Beds of Dorset, Pt. I. The Coast.Proc. Dorset Nat. Hist, and Arch. Soc., 57, pp. 59-93.

CORALLIAN ROCKS OF YORKSHIRE COAST 269

9. ARKELL, W. J. 1937. The Zonal Position of the Elsworth Rock and itsalleged equivalent at Upware, Geol. Mag., 74, pp. 445-58.

10. ---. 1941. The Upper Oxford Clay at Purton, Wilts., and the Zonesof the Lower Oxfordian. Geol. Mag., 78, pp. 161-72.

II. . 1945. The Zones of the Upper Jurassic of Yorkshire . Proc.Yorks. Geol. Soc., 25, pp. 339-58.

12. BLAKE, J. F. and W. H. HUDLESTON. 1877. On the Corallian Rocks ofEngland. Quart. Journ. Geol. Soc., 33, pp. 315-405.

13. BRIDGE, J. 1930. Geology of the Eminence and Cardareva Quadrangles.Missouri Bureau of Geology and Mines, vol. 24, 2nd ser., p. 122.

14. BRINKMANN, R. 1923. Dogger u. Oxford des Sudbaltikums. Jahrb.Preuss. Geol. Landesanst., 44, pp. 477-513.

15. COOPER, G. A. 1937. Brachiopod Ecology and Palaeoecology. Rept.Comm. Palaeoecology, Nat. Res. Council, Washington, pp , 26-53.

16. DAVrES, A. MORLEY. 1907. The Kimmeridge Clay and Corallian rocksof the neighbourhood of Brill (Buckinghamshire). Quart. Journ.Geol. Soc., 63, pp, 29-49.

17. DE LAUBENFELS, M. W. 1939. The Oecology of Porifera, and Possibilitiesof Deductions as to the Paleoecology of Sponges from their Fossils.Rep. Comm. Paleoecology, Nat. Res. Coun., pp, 44-54.

18. FOX-STRANGWAYS, C. 1904. The Geology of the Oolite and Cretaceousrocks south of Scarborough. Mem. Geol. Surv., pp. 40-57.

19. ---. 1892. The Jurassic Rocks of Britain. Mem, Geol. Surv.,I (Yorkshire), pp, 273-407.

20. . 1897. Filey Bay and Brigg. Proc. Yorks. Geol. Soc ., n.s. vol.13, pp. 338-45.

21. HINDE, G. J. 1883. Catalogue of the Fossil Sponges in the GeologicalDepartment of the British Museum (Natural History) .

22. ---. 1890-1911. Fossil Sponges. Mon. Pal. Soc .23. HUOLESTON, W. H. and J. F. WALKER. 1876. On the distribution of the

Brachiopoda in the Oolitic Strata of Yorkshire. Comm . Yorks. Phil.Soc., pp. 7-12.

24. ---. 1876 and 1878. The Yorkshire Oolites. Proc. Geol. Assoc.,4, pp. 353-410 ; 5, p. 411.

25. ---. 1880-1. Contributions to the Palaeontology of the YorkshireOolites (Corallian Gastropods). Geol. Mag., ser. 2, vol. 7, pp . 241-8,289-99, 391-404, 481-8, 529-38 ; vol. 8, pp. 49-59, 119-31.

26. KINDLE, E. M. 1934. The Role of Facies in Stratigraphic Palaeontology.Bull. Geol. Soc. Amer., pp. 409-30.

27. OAKLEY, K. P. 1937. Cretaceous Sponges: some Biological and GeologicalConsiderations. Proc. Geol, Assoc., 48, pp. 330-48.

28. OPPLIGER, F. 1897. Die Juraspongien von Baden. Abd. Schweiz. Pal.Ges., 24, pp. I-58.

29. ---. 1929. Die Kalkschwamme des Schweizerischen Jura. Abh, d.Schweiz. Pal. Ges., 48, pp, 1-31.

30. PHILLIPS, J. 1829. Illustrations of the Geology of Yorkshire, The YorkshireCoast, Part I. 2nd edit. , 1835. 3rd edit., 1875, pp. 40-9, 105-10,128-32 and 324-7.

31. RICHARDSON, L. and A. G. THACKER. 1920. On the Stratigraphical dis­tribution of the sponges of the Inferior Oolite of the West of England.Proc. Geol. Assoc., 31, pp. 151-86.

32. RIETH, A. 1932. Neue Funde spongeliomorpher Fucoiden aus dem JuraSchwabens. Geol. u. Pal. Abh., N.F., 19, pp. 255-94.

33. SCHUCHERT, C. 1911. Palaeogeographic and Geologic Significance ofRecent Brachiopoda. Bull. Geol. Soc. Amer., 22, pp, 258-75.

34. SCHOTT, W. 1930. Palaogeographische Untersuchungen uber den OberenBraunen und Unteren Weissen Jura Nord west-deutschlands. Abh.d. Preuss. Geol. Landes., N.F., 133, pp, 1-59.

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35. SIEMlRADZKJ, J. R. 1913. Die Spongien der Polnischen Jura-formation.Beit, zur. Pal. u. Geol. Ost-Ung., 26, pp. 163-210.

36. SMITH, W. 1829. Memoir on the Stratification of the Hackness Hills,Appendix I, pp, 507-14 in Fox-Strangways [13 above].

37. SMITHSON, F. 1942. The Middle Jurassic Rocks of Yorkshire: A Petro­logical and Palaeogeographical Study. Quart. Journ. Geol, Soc., 98,pp. 27-59.

38. SORBY, H. C. 1851. On the Microscopical Structure of the CalcareousGrit of the Yorkshire Coast. Quart. Journ. Geol. Soc., 7, pp. 1-6.

39. SVERDRUP, H. D., M. W. JOHNSON and R. H. FLEMING. The Oceans,their Physics, Chemistry and General Biology. New York. 1942.

40. TWENHOF1!L, W. H. 1939. Organisms and their Environment. Rept.Comm. Paleoecology, 1935-6, Nat. Res. Conn., pp. 1-9.

41. WILSON, V. 1933. The Corallian Rocks of the Howardian Hills. Quart.Journ. Geol. Soc., 89, pp. 480-507.

42. ---. 1938. The Occurrence and Origin of Chert in the CorallianRocks of Yorkshire. Proc. Yorks. Phil. Soc.

43. . 1948. British Regional Geology: East Yorkshire and Lincoln-shire. Geol. Surv., pp. 46-50.

44. ZEISE, O. 1897. Spongien der Stramburger Schichten. Palaeontographica,Supplement II, pp. 289-342.

DISCUSSIONMr. P. C. SYLVESTER-BRADLEY welcomed the paper and particularly the

detailed sections given of the Hambleton Oolite Series, which would be of greatassistance to local collectors. He was interested to note that Dr. Wilson haddetected rolled sponges in the Hambleton Oolite Series of both Castle Hill andFiley, and asked whether the author considered their presence sufficientlyconstant to provide a faunal distinction between the Coral Rag of the HambletonOolite and that of the much higher Osmington Oolite. It was the speaker'simpression that even within the Hackness Hills the sponges were more abundantin the Suffield area than in the Silpho area.

The following written communication was received from Dr. W. J. ARKELL :I welcome Dr. Vernon Wilson's study of the sponges of the Lower Corallian

Beds of the Yorkshire coast. The group has been neglected in the past, perhapsbecause they have been outshone by the more conspicuous corals. A studyof the unique sponge-coral bed of Hackness is particularly welcome. It is satis­factory also to have a thorough re-description of the Filey cliff section, sodifficult to follow from the existing literature, which varies in age from half acentury to nearly a century and a quarter. The chief value of the description isas a framework into which to fit stratigraphically the ammonites already collectedby Dr. Wilson and to be collected in the future.

My hopes that ammonites would turn up in the Hambleton Oolites in thecourse of this investigation have not been realised; but that makes the recordsthat do exist all the more valuable, and in course of time finds may still beexpected on the inland outcrops.

Since identifiable ammonites of zonal value have been found in the PassageBeds of Filey Brigg and Carr Naze, but not in the Hambleton Oolites, it seemsa pity to abolish the long-established though ill-named Passage Beds and incor­porate them in the Hambleton Oolites. For the present incomplete state ofour knowledge there are by no means too many subdivisions. If there had beenmore in the past, ammonite records might have been more precise and thereforemore helpful. Where the varied constituents of a formation are wedging outagainst a shoreline or an " axis " as here, there may be a number of surprisesmore or less concealed : such as the discovery that part of the Lower CalcareousGrit of Birdsall is younger instead of older than the Passage Beds of the coast.Only from ammonite finds can such conclusions be expected. The rest of thetauna has so long a range that detailed recording bed by bed serves little purpose.

CORALLIAN ROCKS OF YORKSffiRE COAST 271

In this connection it is relevant to mention that the Rhaxella chert (ArngroveStone) of the Oxfordshire-Buckinghamshire border proved to contain an am­monite fauna belonging to the base of the Plicatilis Zone ; that is, later thanboth the Filey Passage Beds and the Birdsall Calcareous Grit. The Rhaxellachert at Purton, Wiltshire, although it has yielded no ammonites, probablycorrelates with the Arngrove Stone.

THE AUTHOR thanked the members for their kind reception of his paper.In reply to Mr. Bradley he said that he failed to see how there could possiblybe any confusion between the reef developments in the lower part of the Hamble­ton Oolite and in the upper part of the higher Osmington Oolite ; the twodevelopments are separated by a considerable thickness of sediment and theirfaunas differ in many respects.

Referring to the paucity of ammonites mentioned by Dr. Arkell, the Authorsaid he knew of the existence of many ammonites being slowly eroded by thesea washing into the bedding planes of these rocks on the coast, but neitherhand, hammer nor chisel can get between the beds to collect them !