The Ice Age in the NorthThe Glaciation of North-Eastern Ireland by Arthur Richard DwerryhouseReview by: J. De W. HinchThe Irish Naturalist, Vol. 32, No. 12 (Dec., 1923), pp. 124-126Published by: Irish Naturalists' Journal Ltd.Stable URL: http://www.jstor.org/stable/25525298 .

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124 ^^e Irish Naturalist* December,

REVIEWS.

The Ice Age in the North,

The Glaciation of North-eastern Ireland. By Major Arthur Richard

Dwerryhouse, T.D., O.S.O., M.R.I.A., F.G.S. Quart. Journ. Geol. Soc, Ixxix, part 3 (1923), pp. 352-422, plates xxiii-xxiv.

This is a paper which should receive the careful attention of all students

interested in the study of the Pleistocene glaciation of Ireland. It deals

with the advances, retreats, and re-advances of the Scottish and Donegal ice-sheets over a wide tract of country in north-eastern Ireland ; and

as it is, in Ireland, the first published study, on modern lines, of the

effects of glaciation on a large scale, it is most welcome. As the

publication of Major Dwerryhouse's work has been greatly delayed, its

belated appearance is the more to be appreciated, and it is to be hoped that in the near future we may have the advantage also of knowing the

results of Prof. Charlesworth's investigations regarding the glaciation of

the north-west of Ireland, results which, we understand, have been ready for publication for some years past. By combining the conclusions of

two specialists in Glacial phenomena, in these neighbouring areas, we

should obtain a comprehensive view of the succession of events during the Ice Age in the North of Ireland.

The region described by the author includes the counties of Antrim

and Down, with parts of Londonderry, Tyrone, Armagh, Monaghan, and Louth, and this large area has been divided into what he considers

to be four natural geographical units?the basaltic plateau of Antrim, the valley of Belfast, the Palaeozoic country of Down and Monaghan, and the igneous districts of Mourne, Slieve Croob, and Carlingford.

Taking these areas in succession, the various Glacial deposits, and other

results of the advances and retreats of the ice-sheets, are dealt with, and

the boulder-clays, gravels and sands, and Glacial drainage channels are

described in such detail that only a few salient points can be mentioned.

In his work on the Glacial deposits of his district, whether boulder-clays or gravels and sands, the author has one outstanding advantage, in that

there are many very definite rock-types which can be identified as occurring in situ in the Firth of Clyde. Among these may be mentioned the

riebeckite-eurite oi Ailsa Craig, the granite of Goatfell, and the quartz

porphyry of Drummadoon ; and the discovery of any of these in the

drifts to the southward is fair proof of the original northern origin of the

deposit in question. Where a suite of these northern rocks is found

any lingering doubt may be set aside. The author mentions a recent

discovery by Mr. Robert Bell of the Ailsa Craig eurite at Drumanewy some

miles west of Randalstown, and rocks of the same type have been found

as far south as Monaghan town. In the account of the Ballycastle district the author gives an interesting description of the terminal

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1923. Reviews, 125

moraines of the last advance of the Scottish ice, and also of the gravel terraces of the Carey River, a more detailed account of which will be

found in the forthcoming Survey Memoir on the Ballycastle district.

The description of the frontal moraines of the Donegal ice-sheet in the

Dungannon-Cookstown area standing "

rank behind rank for several

miles "

is so striking that one would wish that the subject had been

dealt with at greater length by the author.

In addition to his work on the drifts and their included erratics, Major

Dwerryhouse has made a special study of the temporary lakes of late

Glacial times, and their accompanying and resultant overflow or drainage channels. While the ice-sheets, which had invaded north-eastern Ireland

either from the north or from the west, retreated towards their sources,

temporary lakes were formed by the water from the melting ice being

impounded between the slopes of the hills and the ice-sheets, and when

the water of these lakes could find its way over a col or along the hillside

towards ice-free country, it rapidly cut a ravine or overflow channel to

the extent of its powers of erosion. With a farther retreat of the ice,

ways of escape at lower levels were opened, the level of the water in the

lake fell, and the temporary drainage channel was then abandoned. In

any mountainous country which has been^invaded by an ice-sheet these

temporary drainage channels and hill-sidergashes occur in great numbers,

and we are introduced to some hundreds of them in the course of the

paper, which is effectively illustrated by, many figures and plates dealing with this interesting type of temporary erosion. In the Ballycastle district Major Dwerryhouse has mapped some striking examples of these

drainage channels. When the seaward end of Glendun was filled with

Scottish ice, the waters of the lake which had been formed in the upper

portions of the valley could only escape towards the north by the

comparatively ice-free valley of the Carey river, and the main road from

Cushendun to Ballycastle now runs along the floor of the drainage channel

which the outflowing waters of the lake had cut into the lowest portion of the ridge which separates Glendun from the lowlands south of Bally castle. Another great drainage channel in this district is the Inver

gorge, which carried away to the south-west the overflow waters from

the lakes which had been formed to the east and south-east of Knocklayd. In the Slieve Gallion district the author has noted the very striking glens of Carndaisy and Gortanewry which he considers to be the drainage channels that carried the overflow of the temporary lakes of this district

eastward and northward towards the valley of the Bann.

The Mourne Mountains have also yielded instances of these channels, and in the deep flat-floored narrow valley which connects Portadown

with the head of Carlingford Major Dwerryhouse sees the drainage channel of the Lough Neagh basin during the time when the presence of the Scottish ice south of Coleraine prevented the escape of the waters

of that basin towards the north. In Carlingford many drainage channels

have been mapped, the most important being that which carried the

overflow water of the Jenkinstown (glacial) lake into Glenmore. There

are numerous channels on the slopes of Barnavave and Slieve-na-glogh

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126 The Irish Naturalist. December,

which the author deals with in the text, and of these the gorge north

of The Bush station is probably the most important.

Regarding the view, put forward in Figure 12 of the paper, that the

general direction of movement of the Scottish ice across the Mourne

Mountains and across the lowlands of Mourne around Kilkeel was from

north to south or south-east, a word of criticism may be made. That

the lowlands of Mourne are cumbered with immense Glacial deposits of

boulders, gravel, sand and clay, derived from the mountains to the north, cannot be gainsaid, and these deposits may have been incorporated in

the Scottish ice as it moved southwards across the Mourne Mountains, and may afterwards have been deposited in the lowlands. But an earlier

invasion of the lowlands of Mourne by Scottish or Irish Sea ice is evidenced

by the occurrence of a basal boulder-clay, with marine shells, around

Kilkeel, and in the valley of the White Water. In this basal boulder

clay, and in derived gravels, the reviewer, in recent months, found marine

shells in great abundance, in many cases in an excellent state of

preservation, and up to the present fifteen species have been obtained,

including the usual proportion of arctic and northern forms. This

investigation into the distribution of the shelly drift is being carried

out with the aid of a government grant in the gift of the Royal Society of London, and Major Dwerryhouse's paper had already been completed

when the work in the lowlands of Mourne was commenced during 1923. The facts which have been stated point to the conclusion that when the

Scottish ice rounded the eastern slopes of the Mourne Mountains near

Annalong, it moved inland and south-westward across the lowlands of

Mourne, laying down the basal boulder-clay with its marine shells. That

the Scottish ice moved inland from the direction of the Irish Sea, across

the lowlands of Carlingford, and the country south of Dundalk, is also

the opinion of the reviewer, although an examination of the Glacial

deposits of Cooley has, up to the present, yielded no satisfactory evidence

of the presence of shelly boulder-clay similar to that found in the Kilkeel

lowlands.

But the paper must be read in its entirety to be fully appreciated, as there is a great amount of valuable detail which cannot be summarized.

We may congratulate Major Dwerryhouse on the publication of a very

notable contribution to the study of the Glacial geology of Ireland.

J. de W. Hinch.

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