10 Principles of Archaeological Stratigraphy and Excavation Techniques
V. Selvakumar
1. Introduction
Archaeological excavation is a systematic process of digging of natural and cultural layers found in the archaeological sites and landscapes (off-sites) to document, understand and recover the artifactual material remains and ecofacts and to collect information on their contexts in order to understand and interpret the past human behaviour and the cultures on the whole. The natural sediments transported, modified, reworked and added by human agencies as well as natural agencies lead to the formation of the archaeological mounds. The cultural evidence is found within the archaeological sites, in various contexts called layers or strata or locus or activity areas and features. This module focuses on the principles of archaeological stratigraphy, excavation techniques and the Harris Matrix system of recording and illustrating the stratigraphical relationships.
2. What is a stratum?
Soil or rock sediments accumulated due to natural agencies at a particular site as a specific coherent unit is called stratum. Stratum is a Latin word and its plural is strata and in English it is called layer. A stratum is identified and distinguished by its properties such as colour, texture and composition. The idea of strata was originally developed in the field of geology and it was later on adopted in archaeology for understanding the archaeological materials found in the stratified contexts. Sri Charles Lyell, a pioneering geologist, defines stratum as:
“simply a bed, or anything spread out or strewed over a given surface; and we infer that these strata have been generally spread deposits as units of stratification out by the action of water . . . for, whenever a running stream charged with mud and sand, has its velocity checked . . . the sediment previously held in suspension by the motion of the water, sinks, by its own gravity, to the bottom. In this manner layers of mud and sand are thrown down one upon another” (Lyell 1874: 3 as cited in Harris 1979: 46-47).
Although the study of geological layers and strata were developed by the geologists, many archaeologists who excavated the archaeological sites from the seventeenth century have contributed to the development of archaeological stratigraphy. Jacob Asmussen Worsaae (1821–1885) in Denmark (second director of National Museum Denmark), and Thomas Jefferson (former US President) in Virginia, USA, William Mathew Flinders Petrie (English Egyptologist), Heinrich Schliemann (German Businessman), R. Pumpelly, Hubert Schmidt, Giuseppe Fiorelli, General Pitt Rivers, Sir Arthur Evans, Robert Eric Mortimer Wheeler, Kathleen Kenyon, Edward C Harris and many other researchers across the world have contributed to the development of stratigraphic studies.
The strata or layers are macro stratigraphic units. The layers that bear human evidence are called cultural layers and those without cultural materials are called natural or geological layers. The study of geological layers helps us to understand the genesis and processes behind the various rock formations associated with the early history of the earth.
In archaeology, the concept of cultural layers or sediments, which mean the layers that have the cultural materials, is used. These cultural layers are the focus of the archaeologists and archaeological research. As part of archaeological mound formations both the natural layers and anthropogenic layers are studied. Archaeological layers and stratifications are much different in nature, and they are formed due to the activities of natural and human agencies. Because of the complex nature of culture, the strata formation by anthropogenic factors is quite complicated.
An important point to be noted here is the nature of human adaptations, the activities of the natural environments, variations in the impact of natural agencies across the earth (terrestrial and underwater conditions, coastal backwater areas), the temporal contexts condition the nature of archaeological stratigraphy. In the prehistoric ages, as also in the spatial contexts of today where the natural agencies are more influential, the human evidence is found as part of natural stratigraphy. The prehistoric archaeological evidence is found more as part of the natural stratigraphy. However, when humans began animal and plant domestication and when their social lives and culture became highly complex, from the Neolithic period onwards, they produced completely different sets of stratigraphy. Therefore, there is a lot of difference in the statigraphy of the prehistoric sites and later prehistoric and historical sites. These variations are due to the differences in both cultural and natural formation processes.
When we deal with the archaeological sites with abundant human-induced changes, the concept of stratigraphy becomes much different, and this point is repeatedly highlighted by Edward C Harris (1979). According to Hirst, there are three types of archaeological strata, a material deposited horizontally, features that cut the layers, pits, and features that are constructed, i.e. walls (Hirst 1976: 15, as cited in Harris 1979). Therefore archaeological stratigraphy not only has the horizontal layers, but also, complex, multidimensional features created and modified by the humans.
3. Stratigraphy and Principles of Stratigraphy
Stratigraphy is the science of geological layers. It is a sub-discipline of geology that seeks to understand the different types of rock, soil/ sedimentary layers and their relationships. The study of the relationships between the strata is called stratigraphy.
Nicholas Steno’s Fundamental laws
The concepts related to stratigraphy were developed much earlier in history around the 17th and 18th centuries, when the discipline of geology was emerging as a scientific field of inquiry. Nicholas Steno (1638-1686) was the geologist and he was also known as the father of stratigraphy. The Danish born geologist first stated that geological formations are not totally chaotic and certain logic exists behind them. He stated that rock layers are chronological record of earth’s history and past life.
His three fundamental laws are known as laws of stratigraphy (Ben Waggoner, n.d.) and they are:
• Law of Superposition
• Law of Original Horizontality
• Law of Cross-Cutting Relationships
Nicholas Steno’s Laws: Law of Superposition
Law of Superposition states that among the undisturbed strata, the oldest layer lies at the bottom and the youngest layer lies on the top. This may sound as a simple law now, but it is a fundamental law and its recognition helped to scientifically interpret the archaeological evidences encountered in stratified context (Fig.1).
Fig. 1. Complex nature of natural strata and the cultural data. Here in this section from Pattanam in Kerala, the natural layers are found at the bottom-most sand layers, which have limited cultural materials, suggesting limited human intervention. The upper layers have a lot of brick fragments and the reddish clayey loam developed due to anthropogenic activities.
Nicholas Steno’s Laws: Law of Original Horizontality
According to the law of Original Horizontality beds of sediment deposited in water form as horizontal (or nearly horizontal) layers due to gravitational settling (Fig.2). The sedimentary layers generally lie flat. The presence of such layers helps to identify the contexts that formed out of the activities of water. The layers that are originally deposited in horizontal position can change their orientation at a later context due to natural processes.
Nicholas Steno’s Laws: Law of Lateral Continuity
Layers that lie horizontally, extend laterally and they become thinner in the edge area of the basin, in which they are deposited (Fig.3). Normally, layers tend to thin down in the edges of the basin. Similar thinning down of layers may suggest the termination of activities or modification of the terminal of the layers by other agencies. A layer cannot run across in uniform thickness.
Charles Lyell/Steno’s Laws: Law of Cross-Cutting Relationships
According to the Law of Cross-Cutting relationships, an event that cuts across existing rock is younger than that of the disturbed (existing) rock (Fig.4). This law was developed by Charles Lyell (1797-1875). It is also attributed to Nicholas Steno and James Hutton. This law suggests that layer or feature that cuts a pre-existing layer is later in chronology.
Principle of Inclusion
The principle of inclusion states that the inclusions (contents) found in an object or sediments could be older than the sediment or object itself. This law applies to rock formations and also to the archaeological contexts. Normally, the clasts found in the rocks are older than the rocks themselves. This law was proposed by Charles Lyell as principle of inclusions and components.
“The Law of Stratigraphy Identified by Fossils”
The Law of Stratigraphy Identified by Fossils was invented by William Smith who was also known as Strata Smith (Harris 1979). He observed that each stratum was unique and had specific fossils associated with it. If a stratum was found in other area, even though it did not have the fossils found in the earlier locations, based on the characteristics of the contents, this stratum could be assigned to the date of the fossils. However, this law may not be applied to archaeological contexts, because they are unique and much different from the natural layers with fossil remains of organisms (Harris 1979: 111-112).
4. Principles of Archaeological Stratigraphy
The focus of archaeologists is much different from that of geologists in certain perspectives, since the archaeologists’ prime concern has been the humans and their behaviour. Although the environmental context is in evitable in the formation of cultures, the human behaviour and culture have remained as the central focal points of archaeological research. The stratigraphic principles created by the geologists need to be seen from the perspectives of archaeological sites and human behavioural systems.
The ideas related to stratigraphy developed due to the efforts of Nicholas Steno in the seventeenth century. James Hutton and William Smith made important contributions to the development of geology as a scientific discipline. In 1830, Sir Charles Lyell published the book Principles of Geology and the concept of stratigraphy took deeper roots in the later period.
Several archaeologists have worked on to perfect the excavations methods as well as the understanding of the stratigraphy that they commonly encountered in the archaeological sites. The development of archaeological stratigraphy is intimately correlated with the development and refinement of excavation techniques. Edward C Harris concentrated on the various minute aspects and issues of stratigraphy and his publications have added out clarity to the understanding of archaeological stratigraphy.
According to Harris “The principles of archaeological stratigraphy, which is the science by which archaeological sites may be properly understood, are thus everywhere applicable” (Harris 1989, 2014: xi). He adds that the principles of archaeological stratigraphy are those which the excavators apply to the study of archaeological sites, both during excavations and in post-excavation analysis. Harris has redefined the principles of stratigraphy to suit the archaeological contexts.
5. Law of Superposition
The simple law of superposition argues that the bottommost layer is the earliest layer in a section or stratigraphy and the successive layers are later. This law is fine as a fundamental principle, but the materials found in the layers need not be in an undisturbed condition always and the disturbances may selectively shift the materials from one layer to another. Therefore, more than the law of superposition, the integrity of the layers and the disturbance to the layers have to be analysed.
Harris redefines the Law of Superposition as follows:
“In a series of layers and interfacial features, as originally created, the upper units of stratification are younger and the lower are older, for each must have been deposited on, or created by the removal of, a pre-existing mass of archaeological stratification” ( Harris 2014:30).
While applying this principle, archaeologists need to be wary of disturbances to the layers caused by pits and other activities by humans as well as non-human agencies. This law may be applied to the overall formations of layers. Hence, we have to add a condition here that the layers or loci that are found in an undisturbed condition may be interpreted using this principle.
6. Law of Original Continuity
The law of original continuity states that layers normally thin down in the edge of the basin of deposition. Normally lay persons tend to view stratigraphy in a cake-layer in form, but in reality, the layer formations are much more complicated. Another problem with archaeological stratigraphy is that one cannot expect distinct signatures for the changes in each and every activity undertaken by human beings at a site, on the sediments deposited in the ground. A layer may be formed in one moment or one day or it may take hundreds of years. In the settlements of historical period, people wanted to maintain horizontality in the areas of occupation in many of the terrains, unless otherwise dictated by the nature of the terrain, e.g. the hilly regions.
According to Harris Law of original continuity refers: “Any archaeological deposit, as originally laid down, or any interfacial feature, as originally created, will be bounded by a basin of deposition, or may thin down to a feather-edge. Therefore, if any edge of a deposit or interfacial feature is exposed in a vertical view, a part of its original extent must have been removed by excavation or erosion, and its continuity must be sought, or its absence explained” (Edward C Harris 2014 : 32).
A small lense-like feature appearing in a section of a trench could be the edge of a layer hidden behind and beyond the area of the trench. Orientation of the layer is another factor and the layers or loci can have any orientation at a particular site.
7. Stratigraphical Succession
An important point to be noted here is that in the startigraphical succession, the immediately adjacent layers are relevant to the relationships of the layers or loci in the study of stratigraphy. Therefore, it is important to understand the relationship between the layers that lie immediately adjacent to the layers or loci that are excavated. If every unit of layer or locus and the relationships of this locus with the nearby layers or loci could be determined the overall relationships in stratigraphy can be very easily elucidated.
Edward C Harris states that “A unit of archaeological stratification takes its place in the stratigraphic sequence of a site from its position between the undermost (or earliest) of the units which lie above it and the uppermost (or latest) of all the units which lie below it and with which the unit has a physical contact, all other superpositional relationships being redundant” (Harris 2014:157).
8. The Law of Original Horizontality
The law of original horizontality states that the deposits formed in aquatic contexts would be in a horizontal position. Similarly, archaeological sediments would mostly be formed in horizontal contexts. However, in some cases, they may lie in any other position, e.g. in a tilted orientation, following the topography of basin of deposition.
According to Edward C Harris “Archaeological layer deposited in an unconsolidated form will be in horizontal position. Strata which are found with tilted surfaces were originally deposited that way or lie in conformity with the contours of pre-existing basin of deposition.” 2014:157.
Normally, people tend to keep their activity areas in a horizontal position, at least in some areas; and even in the hill regions undulating terrains, are made into horizontal terraces. Humans like to perform their activities on a horizontal plane or position; therefore people create the house floors and living areas in a horizontal position. However, the ponds or pits or other features formed at a site may have the deposits in a different orientations. A city or town or village would exist on one or multiple planes which may exist in the case of towns with citadels, for example Harappa and Mohenjodaro. However, a certain degree of sloping or gradient could be expected to drain the rain water as well as the drainage system in a settlement. Therefore, archaeologists should seek to maintain perfect, flat artificial orientation in an excavated site.
9. Uniformitarianism
The principle uniformitarianism, developed by James Hutton, is another important concept that was used in the early days to interpret the processes behind the geological formations. This law assumes that the processes behind the current geological events and those of the early period are identical. Therefore it is assumed that the processes that are acting upon the geological events are same in the past as well as in the present. This observation is very important, since it helps using analogical arguments.
The Three Types of Archaeological Strata and other components of stratigraphy
According to Hirst, there are three types of archaeological strata, a) materials deposited horizontally, b) features that cut the layers, pits, and c) the features that are constructed, e.g. walls (Hirst 1976: 15, as cited in Harris 1979). Therefore archaeological stratigraphy had to deal with not only the horizontal layers but also, multidimensional features created and modified by the humans.
Based on Hirst’s and Harris’ classifications, the important stratigraphical components encountered as part of archaeological sites are described below.
Surfaces and Interfaces
The concept of surfaces and interfaces are important in archaeological stratigraphy and Edward Harris discusses about these features. Surface refers to a plane or a surface on which activities take place. It is the plane on which objects rest and people walk and use. This surface would be maintained by people at a very fine level in the area that they live, sleep and eat, and to some extent roughly on the streets and rods. The interface refers to the boundary between two layers. It could be just the cut mark of a pit or foundation trench.
Horizontal Layers/Sediment layers
Layers that lie in more or less in horizontal orientation with cultural materials could be categorised as a kind of cultural sediment layers. They lie horizontally because of the startigraphic orientation, gravity and the activities undertaken at a site, e.g. people walking and movement of vehicles. People, when they deposit debris at a site, sometimes, leave it as a pile, or level the surface to keep the area flat. People do not like pits and piles in the main activity areas, which are kept in horizontal, flat orientation.
Sloping, curving layers
Layers that lie in sloping angles in the pits take different shapes, because of the terrain/basin’s shape. They fills in the pits are example for the formation of such layers. Fills deposited in the pits acquire different shapes, according to the shape of the pit feature.
Pits/ Cutting Features
Pits or cutting features have different shapes and they go against horizontality. They cut the horizontal layers and form a basin. Each cut mark can be treated as a separate locus. Pits are those feature dug for various purposes, as robber trenches, burials, foundation pits and post-hole pits and pits for planting trees in ancient times.
Pile/Dump
Piles/dump is an accumulation of soil and cultural debris deposited as a heap, above the ground surface. They are found in the historical sites. These deposits are formed above the ground surface and these piles are also burned after depositing organic materials, .sometimes. They are different from the pits.
Walls/structures/Ramparts and Built features
Walls and structures are artificial accretional features built with clay and/or burnt bricks or other type of materials and they form as important features in archaeological sites. They can be buildings, walls, forts, burial structures and drains. Often, only the parts of such features are found and no complete walls as those found at Pompeii are encountered in archaeological sites.
Natural Features, Landscape Modifications and Off-sites, Tanks, Bunds
Apart from the sites, people may modify the landscape feature to various extents for their activities. They are found in the areas away from the settlements. They could be rivers with embankment, lakes and tanks, canals, highways and various other features. They should also be taken into consideration in the archaeological site formation and stratigraphy. Therefore the concept of landscape approaches is important archaeological research.
10. Dating and Stratigraphy
Another use of stratigraphy is dating, especially, the various features that are found in the site. The stratigraphy offers a relative method of dating features. Even if C-14 dating or other type of dating is obtained, stratigraphic context is used for dating the features. Relative dating is done mainly based on stratigraphy, in relation to the context of the layers. Layers provide contexts for materials, and a date of an object is different from the date of the context in which it is found. Therefore, the date of an object cannot be blindly applied to the context in which it occurs. There the context of associated find appears. Therefore an object has to be correlated with other finds in the context. Therefore, the problem of formation process and cross-checking the other materials are essential for using stratigraphy for dating. Therefore intrusive objects have to be scrutinised in the analysis of material culture found at a site. Objects originally deposited form part of close association or genuine association and objects found in a context without evidence of simultaneous deposition may be considered to be in open association.
Reverse stratigraphy
Reverse stratigraphy refers to materials from the bottom-most part of the site occurring on top and this may occur because of shifting materials due to human activities or other agencies.
Phasing
Phasing refers to grouping of site activities into different phases of activities and this is done based on the evidence from multiple contexts and architectural levels in different parts of the site, in various time context. Excavation of a site in phases would be useful for better understanding the site contexts.
11. Techniques of Excavations
The techniques of archaeological excavations deal with the specific steps or measures to be taken to recognise, identify and document evidence and recover datasets for interpretations, while excavating archaeological sites. The various features, loci, layers/strata encountered in an excavation have to be identified, separately excavated and documented. It is important to identify the interface units in the context of stratigraphy, i.e. where one layer ends another layer starts, both in horizontal and vertical planes. The abstract space between the two layers forms an interface unit. However, it is not necessary that two activity areas have to be marked by distinct layers. The formation of layers may follow a different course depending upon various natural and cultural factors. A particular layer may hide or incorporate multiple episodes of activities. Therefore, more than the colour, the frequency of the contents, and their patterns and the texture and they could help in demarcating various activity areas.
Again, an activity area may overlap with two different kinds of sediments. It is not necessary that the activities that people carry out are undertaken only on one type of sediment. People do not undertake activities according to the colour of the sediment, always.
Trowelling
The use trowel or knife is important for excavating the layers and loci. Trowelling is a method used for identifying the interface units or points of separation of various features such as pit outline, foundation trench and the boundary of the loci. They can be identified by understanding the composition and texture of the sediments. Brushing the surfaces and allowing the surface to dry, getting and the feel of the trowel; all these can help to identify the layer/locus change.
Excavation of Sedimentary Layers
The sedimentary layers are likely to be horizontal in orientation. They may also lie in other orientations too, depending upon the basin or context of deposition. However, one may not expect perfect horizontal positioning of sedimentary layers in the context of archaeological sites. Such orientation can be expected in water-based deposits. Careful trowelling is used for identifying the interface of two loci or layers.
Locus-based Method of excavation and documentation of loci
This method has already been discussed in the module, however the procedure is repeated here.
Locus Based System of Excavation and Documentation
The methods of excavations are described in the module dealing with the techniques of excavations. Here, a brief description of the locus based excavation method is presented. In one type of conventional method of excavations, the digging an arbitrary unit of 5 cm or 10 cm level of sediments is done after gridding the area into arbitrary grids of one square meter or more. In this method, the pits and other distinct features are demarcated and excavated separately. This is not an accepted, accurate method of excavation and the locus-based method in which contexts are accurately demarcated on the basis of colour, texture and content of the sediment layers is a better method of excavation.
Locus based method involves the excavation of activity areas (Loci). In this method, the contexts are demarcated based on colour of the soil, composition and content. In this system of excavations, the datasheets are mainly used to document the information from the activity area in the trenches. In addition, the trench notebooks need to be maintained for a detailed description.
At the site of Pattanam in Kerala, the larger locus that covered the entire trench was divided into small quadrants of A,B,C,D and excavated. This was done to understand if any pattern was seen within the locus, even if it extended uniformly all over the trench. Suppose if a pit or other locus has 40 or 50 cm of deposits of identical nature, the locus can be excavated into subunits of 10 cm at a time, rather than placing all the sediments as one unit.
In the case of prehistoric contexts, where undifferentiated mass of sediments have to be excavated, arbitrary units of 2 cm or 5 cm thick deposits as smaller space-time units and gradually exposing the sediments by scraping the surface is ideal.
Locus Datasheet
The nature of the method adopted would require different types of datasheets. The locus data sheet is essential, if locus based method is adopted. This data sheet would have information on the nature of the sediment, context, cultural importance location and findings.
Top-plans
Top-plan is a method of documenting the features as well as loci that are excavated in a trench. In such a top plan, the distribution of various loci is illustrated. Such top plans are prepared several times in a single day or once in a day of excavation depending upon the need. Whenever new locus is excavated, new top-plans have to be prepared.
12. Archaeological Stratigraphy and Advantages of this Method
In fact always looking for thick strata or layers in an archaeological excavation is not appropriate. In fact the use of concept of layers or strata may be questioned in many a site contexts; especially in the protohistoric and historical sites. The processes behind the formation of thick layers in archaeological sites are contributed by natural as well as human agencies. However, the human activities and observation of the patterns of behaviour would require to focus on minute traces of activity areas which might occupy only a tiny part of a layer. While layers are larger contexts of deposition, the activity areas may be identified as loci representing the smaller events. Excavation by locus or context is an ideal method in most archaeological sites. Excavation of layers or contexts after proper documentation is important. The method in which each context is numbered and excavated and it is ideally suitable for most archaeological sites. Perhaps it is the most accurate method available
Excavation by Arbitrary Units
Excavation of arbitrary units was an old method, not suitable for proper excavation. It is known as spit method. Arbitrary units of 1 or 2 to 5 cm are excavated in some contexts for excavation. This method should be used only in exceptional cases, if the sediments cannot be differentiated. Mostly natural sediments of very high thickness could be excavated using such arbitrary units. It is used in prehistoric sites with thick deposits of undifferentiated nature. This method may be more suitable in contexts where natural formations are dominant and where the contexts cannot be distinguished into micro units based on their characteristics.
Excavation of pit
Pits are a form of disturbances; they could be part of systemic or post-depositional contexts. Pits that are dug for various purposes, post-holes, and later disturbances due to agricultural activities are often encountered in archaeological sites. Pits are identified by the variation in soil colour, composition and texture. Soft soil sediments are useful for demarcating the pits. Identifying the pit outline and removing the pit deposits before proceeding further is very important. Over excavation of the pit materials may be important and the materials of later contexts should not be let at the contexts of earlier origin.
Excavation of Brick Structures and Walls
Brick structures are often encountered in archaeological sites of the historical period. The brick structures have to be excavated carefully. The isolated bricks found in a context while excavating sediments should not be removed, since they could be the top-most part of a hidden brick structure. Taking sections across the walls or brick structures could be useful in identifying the relationships of a structure with other associated features. The working level of a structure has to be identified during the excavations. Its foundation, construction, use and abandonment have to be observed.
Floors
Floors are features often associated with buildings. Floors reflect the law of horizontality and people normally like to have the floors in a flat or horizontal orientation. People like hard, smooth surfaces as the floors and hence, thin, compact features could be found in the excavation.
Mud-bricks and Mud-walls
Mud-bricks and mud-structures may be identified on the basis of soil hardness and colour variation. Mud-bricks are not easy to identify. The hardness and the brushing and use of knives and trowel could help to locate such features.
Dump/Pile of debris
Pile/dumps are often accumulation of soil or garbage or brick fragments and other materials above the surface and they have the negative shape to that of the pit, i.e. they resemble the shape of a hillock on arch in their contour. They may appear like a pit in the top-most point, but extend horizontally. Often materials discarded by people as part of site maintenance, such ceramics, lithic and organic materials and debris of buildings lead to the creation of such features.
Excavation of Burials and Skeleton
Delicate skeleton Excavation of burials and other delicate features may require the services of specialists or well trained hands. The burials require more careful excavation of delicate bones. The burials have to be documented carefully before the bones are lifted.
Lifting by Undercutting
Objects and other features may be lifted, by undercutting along with the sediments underneath. This method would be useful to excavate the skeletons for display in museums. This method could preserve the contexts and the objects together. They may be excavated latter in the lab.
Screening/Sieving Methods
Screening/Seiving the soil or excavated sediments is very important for recovering all kinds of material remains. The excavation without screening would not provide all kinds of data. Screening may be time consuming, but it is inevitable. Dry sieving can be adopted in some contexts. Wet sieving can be used in for wet sediments.
Dry screening is important to collect all kinds of artifacts in an excavation. Dry screening is possible, when the sediments are loose, dry. Different types of (meshes) of sieves or screens could be used depending upon the context. Micro-beads and micro splinters may escape normal sieves/screens. Sampling strategies could be used for screening through micro sieves, which could recover micro debris.
Observations required on the locus/loci or stratigraphic Units
Edward Harris mentions about the observations and documentation required for each unit of stratification or locus. He states that the following are required as part of documentation.
1. Written description of the contents of the unit and the all type of physical relationships with other units (e.g. above, below, touching, not touching, later and earlier units).
2. A top-plan showing the boundary contours, elevation, topographical relief, and the areas of the unit destroyed and disturbed by the later features.
3. A section drawing showing the limits or boundary contours and soil composition
4. A plan of the disposition of the finds from the unit.
Characteristics of a Layer or Deposit or unit of stratification
Characteristics of deposits are attributes or variables of a deposit. They are described by Harris as listed below (Harris 2014: 51-52)
1. Face or Surface: Face refers to the original surface of the layer and it is different from the lower surface of the layer. It is called interface. Upstanding face refers to the walls. The boundaries are important since they mark the termination of an activity.
2. Boundary contour: It refers to the unique extent of vertical and horizontal extent of a layer.
3. Surface Contour: Surface contours are the reliefs of the layer or stratification.
4. Volume and Mass: Refer to the dimensions of the layers.
5. Stratigraphic position Its exact location in relation to other loci
6. Chronology or date
7. Relative dating and association.
Relationships in Stratigraphy: Harris Matrix system
Harris matrix is an illustrative scheme used for illustrating the relationships among the various loci or layers excavated at a site. This system was developed by Edward Harris and hence, it is known as Harris Matrix. It visually conveys which loci are earlier, later and contemporary. The Harris Matrix System is a useful method for documenting the relationships among the various loci. Since the number of loci or contexts excavated in a trench the relations cannot be explained in a simple terms.
Harris Matrix conveys complex relationships in stratigraphy in a simple manner. This system offers a good method for illustrating the stratigraphic relationships. Here each locus or activity area is given an identification number and sometime the cut marks and the surfaces may also be given separated identification numbers. The id of a locus is placed in a rectangular box and the features that are touching each other are connected by a vertical line. The top-most layer occurs on the top and the other loci or layers are illustrated below and they are placed in same level if they occur in the same depth. Different methods and conventions could be used in the illustration of the Matrix of a trench. Different shaped boxes instead of rectangle grids ( e.g. boxes in the shape of pits to display pits, or walls to display walls) could also be used. Compare the Figs.5 to 8 to understand the benefits of Harris Matrix.
- Summary
The idea of stratigraphy and the principles of stratigraphy were originally developed in the context. The important principles of geology have been applied to archaeological stratigraphy for understanding the relationships among the various loci or layers.
The Law of superposition, the most important law of stratification, argues that the bottom-most layer is the earliest layer and the top-most layer is the latest in a stratigraphic segment.
Law of Original Horizontality suggests that the sediments deposited in water-based environments lie horizontally, due to the gravitational activity.
Law of Cross-Cutting Relationships: says that An event that cuts across an existing rock is younger than the disturbed rock.
Edward C Harris has modified the original principles of stratigraphy to suit the archaeological contexts.
- Law of Superposition
- The Law of Stratigraphical Succession
- The Law of Original Horizontality
- Law of Original Continuity
An important point to be remembered is that in the context of archaeological sites of later prehistoric and historical period the focus is not on the thick layers of strata and the results of minute activity areas that may be hidden in a thick layer. The focus should be on identifying the thin layers and sedimentary contexts and activity areas.
The activities of various factors have to be studied, and one cannot blindly apply the law of superposition, among other factors, the artefact distribution, enquiry with the local landscape history, farmer’s activities who could tell about the development and landscape modifications are also important in understanding site stratigraphy.
Various excavation techniques are applied to carefully identify and excavate, different features such as building, structures, floor and foundation pits. Understanding formation process is essential for employing right techniques in excavations. The primary objective of the excavation is to identify and recover artifacts and features and to understand the relationships between various contexts that are excavated.
Harris matrix is a method used for illustrating the stratigraphical relationships. It was developed by Edward C Harris as a technique for easily illustrating the complex relationships among the various contexts and layers that are excavated.
Web links
- http://www.ucmp.berkeley.edu/history/steno.html
- https://answersingenesis.org/creation-scientists/great-creation-scientists-nicolas-steno/
- https://www.britannica.com/biography/Nicolaus-Steno
- http://www.flmnh.ufl.edu/natsci/vertpaleo/ formation99.htmaucilla12_1/formation99.htm”>http://www.flmnh.ufl.edu/natsci/vertpaleo/aucilla12_1/
- www.harrismatrix.com/book/Practices_of_Archaeological_Stratigraphy.pdf
- http://www.archaeology.ru/Download/Harris/Harris_1989_Principles.pdf
- http://www.harrismatrix.com/history.html?reload_coolmenus
- http://www.harrismatrix.com/
- http://users.clas.ufl.edu/davidson/Proseminar/Week%2012%20Time/Harris%201979%20laws%
20of%20stratigraphy.pdf - https://keilynm.files.wordpress.com/2015/06/barker-techniquesarchaeologicalexcavation.pdf
- https://faculty.washington.edu/jkstein/pdfs/Stein%201990%20Archaeological%20Stratigraphy.pdf
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rsson.pdf - http://evolution.berkeley.edu/evolibrary/article/history_12
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