The Stratigraphic Sequence: A Question of TimeAuthor(s): Edward C. HarrisReviewed work(s):Source: World Archaeology, Vol. 7, No. 1, Burial (Jun., 1975), pp. 109-121Published by: Taylor & Francis, Ltd.Stable URL: http://www.jstor.org/stable/124112 .Accessed: 10/07/2012 16:02

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World Archaeology Volume 7 No. I

The stratigraphic sequence: a question of time

Edward C. Harris

The concept of stratigraphy has 'more general significance and application' than any other in archaeology (Heizer I959: 2I5). Sir Mortimer Wheeler felt that the first duty of the excavator was to attend to his stratification (I954: 40). Yet for all the agreement in

principle, there are no agreed definitions, stratigraphy and stratification being used

synonymously:

the principle of stratigraphy, which is that an object left on or in the soil at any given time will be found at a lower level than one deposited later (Wood I965: 28I);

or

the principle of stratification: the fact that (unless you stir them up) the discarded letters in your waste-paper basket will have earlier dates near the bottom and later dates at the top (Piggott I959: 34).

These authors imply that objects are inseparable from the principle and that the physical position of a find or stratum inherently states the principle of stratigraphy-stratification.

Objects and stratigraphy are a subject which needs a fuller discussion than can be

attempted in this paper. Behind the other point, the location of strata, however, lurks the

spirit, if not the letter, of the inaptly named 'law of superposition'.

The commonest use of this word in geology is when stating or applying the knowledge that in a stratified series of sedimentary rocks the upper strata are, normally, the newer. Although often called the 'law of superposition', this does not appear to be so much a 'law' as a necessary and obvious corollary attending the fundamental axiom that these rocks are hardened sediments which were laid down in successive layers (Challinor I964: 238).

Although one cannot refer to the deposits of an archaeological site as 'rocks of hardened sediment' or subject such strata to an analysis based on geological axioms and corollaries, it appears that many archaeologists have accepted such a course.

Geologists, in ordering their discoveries, already used the idea of stratigraphic succession, the principle that when successive layers or strata are observed in position, the underlying ones are the earliest. Using this principle, and the characteristic remains of extinct plants and animals within the strata - the type fossils - a succession of geological periods or epochs was established and gradually extended to cover the world as a whole. Archaeologists realized that layers of deposit on archaeological sites could be studied in the same way, and that for each site a coherent sequence of occupation could be worked out in terms of the successive strata. The stratigraphic method remains today the essential basis for archaeological excavation (Renfrew I973: 23). HWA

Burial

Ix o Edward C. Harris

The truth of this statement is not disputed in one sense: archaeology received one of its fundamental tenets from another science without a redefinition of either the concept or the terms associated with it. The result can be seen as one where 'the variety of aims and

interpretations is a grave weakness based not on error, or personal idiosyncrasy, but

upon ambiguous and inexplicit terminology, differing use of the same terms by different individuals' (Clarke I968: 2I).

This situation is due for reassessment if we are to make proper use of the concept of

stratigraphy to construct our relative chronological sequences and to test chronologies composed in other ways and fashions. A redefinition of 'stratigraphy' and 'stratification' is thus proposed below.

Stratigraphy is the descriptive study of archaeological strata (the smallest recognized divisions of a site, physical or otherwise, generically referred to as 'layers'), their

occurrence, soil or filling content, artefact content, succession, and classification with a view to arranging them in a chronological sequence. Stratigraphy is not a principle but rather an area of study. Stratification is any number of relatable deposits of archaeological strata which are the result of 'successive operations either of nature or mankind' (Wheeler in Rapport and Wright I963: 47).

The redefinition of 'stratification' necessitates the use of the stratigraphic sequence, which is a name for the relative chronology of a site as deduced from its stratification. Constructed by the rearrangement of stratification (see fig. 23 G and H), it is a statement in four dimensions, the fourth being Time which has an 'event' as its smallest element

(Garnett in Abbott I962: v). This reorganization of strata may be ordered and controlled

by the corollary of 'superposition', but in practice it is also guided by the excavator's sense of time and his comprehension of how a people constructs its buildings and

organizes its topographical situation. The principles involved in this task are not

stratigraphic, but derived from a study of human activities. Such principles are numerous, a point presciently made by Wheeler: 'the first rule about stratification is that there is no invariable rule' (1954: 45); but it is by the application of those principles that stratifica- tion is analysed and stratigraphic sequences built.

Sections and plans in stratigraphic analyses

When studying stratification, many excavators rely on the section as a way to work out the relationships between the layers of a site; the layer plan is usually ignored in strati-

graphic analysis, partly because the standing section or baulk (OED: 'The original sense was perhaps "bar" . . .a strip of ground left unploughed. ... A blunder . .. an omission. ... A stumbling-block, obstacle') works on an excavation against the recovery of the plan of each layer. The position of baulks is most often determined by the presence of a building, especially one of stone, and any baulk alignment not at a right-angle to the

building is considered untenable. This geometric criterion has little import as the section on the face of the baulk, cannot, except on the simplest sites, reflect either the vagaries of individual layers or represent any but the most local of stratigraphic sequences. Arguments of chronology or of the sequence of a complex stratigraphic situation based on sectional analysis must be suspect or completely fallacious.

It is now apparent that proper stratigraphic reasoning must be founded on plans

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Figure 23 The division of section A into its smallest units in E, and the reorganization of those divisions into an explicit stratigraphic sequence in

G, is mirrored in the matrix form as B, F and H

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.

II2 Edward C. Harris

showing the area of each and every layer and incorporating detailed spot-heights, augmented as necessity arises by sectional data. Using such methods it is possible after excavation to reconstruct other sections where appropriate and to make composite phase or period plans. The current reliance on the section in stratigraphic research should be replaced by a balanced recording method which would include, first and fore- most, the planning of all layers.

The section will in many cases be the correct analytical method for solving a local

problem, but in a general sense controversy has raged over the issue of what a drawn section should look like. The problem is defined by saying that there are three ways of

drawing a section: realistically, stylistically, or compromisingly (Webster I963: fig. I5). This controversy centres on the appearance of the section, and misses the question of its utilization. If a section is to express the vertical plan of a particular area of a site, any of the

draughting methods may suffice. However, if the purpose is the illustration of strati-

graphic sequence, realistic or compromising draughtsmen must resort to a stylistic representation, as the section represents only an initial and not a final statement of

sequence. The labelling and defined limits on layers in a stylistic section (e.g., fig. 23 A) are decisive criteria for the interpretation of succession. These aspects of controlled

recording are normally absent on naturalistic and compromise sections. In Archaeology from the Earth, Wheeler set down definitively the requirements for a

correctly recorded section; one of his illustrations (fig. 23 A) appears in this paper. That section omits enumerations for the 'cut' line of the posthole and of the earlier wall, and also the line which we are told represents the eroded surface of a street. Each of these elements is evidence in the section for a past event, but in this particular example the author did not follow his own observations to a conclusion: 'traffic gradually wears the street into a hollow . . . the passing of time may be represented stratigraphically by denudation no less than by aggradation' (Wheeler 1954: 75). The oversight has been remedied here (fig. 23 E) by the addition of extra layer numbers: layer 14 is the posthole cut; layer i8 is the cut of the foundation-trench for the earlier wall; and layer 20 is the line of the eroded street surface. Other changes in numbering have been made so as to have one seriation on this section.

Thus slightly amended, Wheeler's section can be used in the construction of a strati- graphic sequence, for it is decisively drawn and accurately labelled. Because sections ought to be used in conjunction with other records in establishing succession, they should be translated into a form common to the other categories. We shall return to this point in the final part of the paper.

The correlation of stratification

Correlation is a subject usually mentioned in methodological essays, but most writers fail to say how they carry out the process. Two examples do exist, the later (Alexander 1970: fig. II) being a more difficult version of the earlier (Kenyon 1952: fig. 13). The method consists of a written interpretation of a layer, followed by a tabulation of the various, correlated numbers assigned to that layer. At the same time the layers are arranged into periods, but at no time are any direct stratigraphic relationships, except equations, expressed. This system may work well if the amount of data is small. It is of little use on

The stratigraphic sequence: a question of time 113

sites with a complex stratification as, for example, the Lower Brook Street at Winchester, where in I965-7I excavations directed by Martin Biddle for the Winchester Excavations Committee recovered some ten thousand units of stratification relating to the Roman, Anglo-Saxon and medieval periods. With the correlation method, it is quite impossible to

analyse so large a material and maintain a sense of structural continuity or stratigraphic succession. Indeed, the term 'correlation', seems out of place as a description of the object of the exercise which ought to be 'the putting together of parts or elements so as to make a complex whole; the combination of immaterial or abstract things, or of elements into an ideal or abstract whole' (OED: synthesis). The correlation of stratification, like the use of sections, is only a part of the process leading to the demonstration of a stratigraphic sequence.

The synthesis of stratification

The aim of the approach proposed is to combine the entire stratigraphic data of a site into a single, coherent diagram. The different record categories - sections, plans, and site-notes - are each examined separately. They are then tested against each other and the results of this synthesis are placed on a pro forma sheet of small rectangles (fig. 24). The method for placing the information on the sheet is set out in fig. 25 F-I: in F, layer 3 occupies a single box and has three possible relationships with any other layer, it is over

(later than), under (earlier than), or equal to (correlates with, contemporaneous with) any other layer; in G, layer 3 is under layer 2; in H, it is the same as layer 4, and in I, it is over layers 5 and 6. Fig. 25 I could be called a 'layer complex' and may be the beginning of a

stratigraphic sequence. A site-notebook form of this small layer complex is shown in fig. 25 J. Inherent in the previous paragraph is the transformation of a group of layers into

common, abstract units. The physical dimensions, for example, of a wall, a posthole, or the smallest patch of soil, are ignored. All layers are reduced to the same value as each represents an event in time. If the quality of the site records allows, it will be possible with such events to build a chronological sequence from the excavated material.

Akin to this transmutation of layers is the idea that any unit of stratification can occupy the space between two lines (fig. 25 A-E). It is thus possible to project the abstract, time dimension of a layer beyond its physical dimensions (fig. 23 E, G and J). In fig. 25, two types of stratigraphic units are demonstrated: B and E are examples of vertical layers; D is a horizontal layer. In effect, there is no reason to differentiate between these two layer types, except that the first group is usually the cause of most stratigraphic problems. E, a cutting, can destroy pre-existing physical relationships, while B, a wall, may serve as a barrier to the stratification which post-dates its construction. The two groups are brought into a common focus by the fact that they are all accumulations in the relative

sequence of a site, regardless of whether they are the result of denudation or aggradation. Returning to fig. 23, the last paragraph will be treated by example. In B, section A has

been reduced to a matrix diagram which mirrors that section but does not interpret it; D, in like manner, is complementary to section C, the point being that unless one

interprets or reorganizes a section, it is only an implicit statement of stratigraphic sequence. In E, a reorganization of section A is begun by splitting it into its smallest divisions, enclosing each with the abstract format mentioned above. At this stage the value of the information is equivalent to F, in which each layer of the section is seen as a

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The stratigraphic sequence: a question of time 115

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ECH X5 [ L6IJ Figure 25 A-E represent an abstract dimension for layers (see fig. 23). F-I demonstrate the method of constructing stratigraphic sequence-diagrams in the matrix pattern

disconnected event. With the movement of the layers in G, the interpretation of the section is complete; its stratigraphic sequence is demonstrated in H. I is the same

sequence as H, but only the structural equivalents of some of the layers are included. The final parts of the fig. 23, J and K, illustrate that Sir Mortimer Wheeler was correct with regard to the obliteration of the physical aspect of certain relationships in section C, but incorrect in another sense as the abstract layer can replace the physical one. In many situations on site, one has 'excavator's trenches', which are referred to as features, pits, or

robbing trenches. In such cases, it is the responsibility of the excavator, in his inter-

pretations, to bridge such gaps, to 'make a reasoned guess on the basis of insufficient information' (unattributed in Cole and King 1968: 98).

On a complex site, one can put the sections (fig. 26), plans (fig. 27, E, F, G) and other

stratigraphic material (fig. 27 J) into such diagrammatic form. The different categories, when combined (fig. 27, J and K), should produce the full stratigraphic sequence for the site. Fig. 28 is the sequence for the Winchester Excavations Committee's 197I site at the Assize Courts (Biddle 1975: in press). In that excavation, a section was cut across the ditch of the Iron Age enclosure (plate 9) located on the western side of and partly below the

present town. A large baulk (plate io) was maintained in the centre of the trench until the final days of the work. Its removal accounts for the many equations in the middle of fig. 28; the duplication of numbers is due to the presence of two trenches, each with its own series.

The matrix diagram contains layers which relate to the later Iron Age and all later

periods, and it is a statement in four dimensions. The three dimensions of each layer

o 0 C d

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Figure 26 The stratigraphic 'sequences of sections A-D are shown in matrices a-d; a + b + c + d is the revised sequence derived from the combination of the sections

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Figure 27 Plans E-G are reduced to the sequences e, f and g, which are combined in H. J presents the merger of I (see fig. 26), H, and all other stratigraphic information; the resulting stratigraphic sequence for this imaginary site is annotated in K

I

- Trench V . 1_ Trench IV V ECH Assize Courts North 1971

Figure 28 The stratigraphic sequence of the Iron Age ditch at the Assize Courts site, Winchester, is shown in this matrix drawing. Part A has all data plotted and Part B illustrates the corrected sequence which contains no ambiguous stratigraphic relationships

The stratigraphic sequence: a question of time II9

have been considered along with their temporal relationships. The lines connecting each three-dimensional block in the diagram can be considered as threads of relative time. This method of presenting a stratigraphic sequence might be seen as a form of critical

path analysis: 'The fundamental features of critical path analysis are that it is a one way network, that the links are measured in units of time, and that the critical path is the

longest path in time through the network' (Cole and King I968: 571). In other words, the most valid relationship, between a layer and all those which predate or postdate it, is that with the layer which is the latest of all layers which predate the layer in question, and that with the layer which is the earliest of all layers which postdate that given layer. It is for these reasons that certain of the relationships drawn in A of fig. 28 have been deleted as irrevelant in B of the same figure. The stratigraphic sequence of a more complex site, the South Gate of Winchester, excavated in I97I, was constructed after a rigorous analysis in the manner described above, and is presented in fig. 29.

Conclusion

For the purposes of this paper, the form of the stratigraphic sequence as presented, for

example, in fig. z8 will not be further discussed, and certain topics have been ignored. Most important among these is the introduction of dating evidence. The paper has

attempted to show that questions of time are paramount in the understanding and construction of stratigraphic sequences. The aim of excavation is four-dimensional and not three-dimensional recording and reconstruction. Sections are inadequate for the

presentation of stratigraphic sequences of any complexity, as they are two-dimensional in format, only implying the third and fourth dimensions. Correlation is a method of

equation and not one of synthesis; it is only one part of the process of building relative

stratigraphic chronologies. The synthetic method of stratigraphic analysis introduced in this article, if used during excavation, would probably ensure that every scrap of stratifica- tion made its proper contribution to the story of a site and that there were no layers left 'in limbo' (Alexander 1970: 94) after the fact of excavation. It is an explicit system which demands answers to questions of stratigraphic succession at the most correct moment for such inquiry - during excavation.

Acknowledgements

This writer began his archaeological education in Winchester, where between 1967 and I97I he participated in the excavation programme of the Winchester Excavations Committee under the direction of Martin Biddle.

In the I972 that education was tested by a period of excavation in Norway which resulted in the framing of certain questions regarding stratigraphic procedure in the feld. In this case, I extend my thanks to Forste-konservator Asbjorn E. Herteig and his staff for their many considerations proffered during my stay on the excavations at

Bryggen in Bergen. The impetus to move from inquiry to analysis occurred as a result of my association

-with the Winchester Research Unit and my specific task in processing the records of the Lower Brook Street site for publication. I am extremely grateful to the members of the Unit for their support of the investigations outlined in the paper. In particular, I wish

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constructed in the fashion of figs 6 and 27, but from a larger corpus (406 layers) o

stratigraphic material

201 E 202I203

stratigraphic11551 mateLrIal

stratigraphic material

The stratigraphic sequence: a question of time I2I

to thank the Director, Martin Biddle, for the opportunity to undertake this work and for permission to use Winchester Excavations material prior to its final publication, especially plates 9 and Io, and figs 28 and 29, which are the copyright of the Winchester Excavations Committee.

In addition, I thank Professor D. M. Wilson, P. A. Rahtz, L. J. Keen and G. N.

Clarke, who provided valuable criticisms on the original text. Final credit is due to L. J. Keen for pointing out to me the importance of its layer plan in stratigraphic analysis.

I.x.I974 Winchester Research Unit Winchester

References

Abbott, E. A. 1884. Flatland, a Romance of many Dimensions. Oxford. 1962 edn.

Alexander, J. 1970. The Directing of Archaeological Excavations. London.

Biddle, M. I975. Excavations at Winchester I97I. Tenth and Final Interim Report. Antiquaries Journal. 55 :in press.

Challinor, J. I964. A Dictionary of Geology. Cardiff.

Clarke, D. L. 1968. Analytical Archaeology. London.

Cole, J. P. and King, C. A. M. I968. Quantitative Geography. London.

Heizer, R. F. I959. Stratigraphy and stratification. The Archaeologist at Work. R. F. Heizer, ed. New York.

Kenyon, K. M. 1952. Beginning in Archaeology. London.

Piggott, S. 1959. Approach to Archaeology. Cambridge.

Renfrew, C. I973. Before Civilization. London.

Webster, G. I963. Practical Archaeology. London.

Wheeler, R. E. M. I954. Archaeology from the Earth. Oxford.

Wheeler, R. E. M. 1963. New techniques in archaeology. Archaeology. S. Rapport and H. Wright, eds. New York.

Wood, F. S. I965. Collins Field Guide to Archaeology. London.

Abstract

Harris, E. C.

The stratigraphic sequence: a question of time

The stratigraphic sequence, constructed by the correlation and analysis of the stratification of a site, should form the basis for the division of the site into the phases and periods of its develop- ment. The article examines certain aspects of the method of stratigraphy in archaeology. It discusses a method of stratigraphic analysis which makes it possible to present, in a single diagram, the entire stratigraphic sequence of a site, even where this is of great complexity.