21 Exploration and surface collection of tools if any

Dr. Debasis Kumar Mondal

Contents:

1. Introduction

2. Archaeological site

3. Exploration

4. Techniques of surveying

4.1.    Desktop Study

4.1.1   Documents

4.1.2   Maps

4.2.    Surface survey

4.2.1.   Field walking

4.3      Aerial Survey

4.3.1.    Aerial Photography

4.3.2.    Aircraft and Satellite Imagery

4.4       Geophysical survey

4.4.1.    Resistivity surveying

4.4.2.    Magnetometer surveying

4.4.3.   Magnetic surveying

4.4.4.    Metal detector

4.4.5.   Ground penetrating radar (GPR)

4.5.     Geochemical survey

5. GIS

6. Instruments used in site survey

7. Surface collection

8. Recording of archeological sites

Summary

Learning Outcomes:

Once you have studied this module you will be able to:

•  define and understand archaeological exploration;
•  understand the traditional techniques of finding a site;
•  understand the new scientific techniques used to identify sub surface activities without excavating a site; and
•  learn the method of systematic collection and different remnants of human activities of the past.

1. Introduction

Archeological anthropology is a sub discipline of Anthropology that deals with the past human culture with the help of material remains found from the archeological sites. Sites not only preserve the material remains of the past human activities but also preserve the total cultural landscape. Archeologists are interested to find out the sites both in primary and secondary context. So finding of archeological sites is a crucial part of archeological study and project. There are number of techniques used in archeology to find out a site which was inhabited by early men. The technology has been revitalized with invention of new techniques from sixteenth and eighteenth century. According to Fagan (1999) there are three stages of archeological fieldwork-

•  finding archeological sites,
•  assessing the sites and
•  archeological excavation.

The present module will be made on exploration or site survey. Before get insight of the topic it is very important to know what site is and how it could be recognized.

2. Archaeological site

Site is a place where there are remnants of human activities. There are different types of archeological sites. Such as habitational site, factory site, camp site, butchering site, burial site. Different types of site preserve different types of artifacts. For example habitational site is identified with the presence of huge number of potsherds. Whereas factory site have different finished and unfinished tools, cores and chips. The distribution of artifacts on the surface, helps archeologists to find out the type of a site and sub- surface condition on which the excavation strategy will be framed. Archeological sites are found in different ecological and geographical zones like plateau area, terrain, caves etc. Before going to the field desktop study helps to understand some basic criteria for potentialities of the sites for human habitation like nearby water sources, availability of resources of food and raw materials for making tools and protection from predators. Noticeable earth work, distribution of artifacts, vegetation cover, soil discolouration and surface finds are the key indicators of a site.

3. Exploration

Exploration or site survey is the searching of sites where past people lived. It incorporates different methods and techniques which archeologists use to find out past human activities. Systematic exploration gives clue of getting the relics of past culture. During exploration a site is mapped with respect to the geographical condition. The artifacts found on the surface are plotted and sometimes collected to know the nature of the site and concentration of artifacts in a particular location.

4. Techniques of surveying

The techniques of surveying of archeological sites are broadly classified into two- traditional and modern. Traditional techniques include field walking. Remote sensing method is a modern and major technological achievement of ‘nondestructive archeology’ i.e. the study of site without excavation or collecting of artifacts. Remote sensing includes different techniques like aerial photography, satellite images, geophysics and side scan radar. The technique of remote sensing is to capture geographic data by sensor at some distance from the surface under study.

Prehistoric sites are found either by accident or deliberate archaeological surveying. Archeological sites are sometimes discovered accidentally during railway construction, building construction, earthquakes. Investigations also have been taken to explore new areas and sometimes systematic attempts have been made to increase knowledge about the areas which are already explored. Techniques of surveying a site are broadly classified into four types (Grant et. al. 2008):

• Desktop study
• Surface survey
• Aerial survey
• Geophysical survey
• Geochemical survey

4.1.     Desktop Study

Desktop study is an office based investigation of existing records such as different maps, photographs, historical sources, archaeological records and documents.

4.1.1.    Documents

There are different types of documents like legal documents, Government tax record, economic record, pictorial and written records, archeological records and oral documents. There are known archeological sites such as Great Wall of China, Stonehenge etc. local people also provide clues about lost sites and archeological evidences. Some sites are lost to both archeologists and local people such as Altamira and Lascaux caves in Spain. Knowledge also exists in the records of previous archeological survey undertaken in a particular site or area. Archeologists use existing documents which is one of the major sources of locating an archeological site. Documentary evidences are usually very detailed and specific and sometimes much generalized. There are enormous available documents to locate an archeological site from written sources to maps. Written sources are available in archives and data bank. Sometimes documentation in Museum also helps to locate a site. Map is also one of the most important sources of document to find a site. Other document types used to locate an archeological site are pictures, photographs and name of the place sometimes is very useful to know the history of an area and probability of being an archeological site.

4.1.2. Maps

Maps provide large quantities of archeological information. Cartographers developed many techniques of communicating information graphically. There are different types of maps used in archeological surveying. Ordnance survey (OS) maps give a detail country wise description in reference to the grids. Topographical maps provide information like ancient settlement pattern, surrounding vegetation, soil types, nature of resources and also prehistoric trade roots. Topographic maps also helpful to identify sites along the dried up river channels or either the site is potential for human habitation. Planimetric maps show the features of archaeological sites and are used to record the details of archaeological sites. There are also other type of maps including soil types, climates, land use and vegetation. Site plans are prepared by archaeologists to record the horizontal provenance of artifacts and other features of the site. The maps are drawn from datum point from which grid of squares can be laid out over the area of the site. The grid has a system of coordinates which is vital in recording surface finds during the survey.

4.2.  Surface survey

Surface survey is non-destructive visual survey at ground level primarily to find new sites. It includes field walking, surveying and also planned aerial photography. The landscape, geomorphological features, soil types imply the past human activities on the site. Surface survey is also done with the help of topo sheet, GPS and other instruments.

4.2.1.   Field walking

The most traditional method and simplest procedure of searching a site is field walking. A large scale survey is continued day after day, week after week. It is not possible to survey the total sites especially in those cases where the site is too much extent. Observation is the primary key of archeological survey. Observation has been made on fluctuation in the character of the ground surface and recognition of ancient artifacts lying upon the surface. There are two types of survey extensive and intensive survey. In extensive survey the investigator examine only conspicuous and accessible sites. It is a systematic survey of a relatively limited area. An intensive survey involves collecting as much information of the entire area and surrounding sites. In intensive survey is conducted by covering a whole area by walking. Transects are sampling lines used to survey single site or total landscape usually aligned to North-South direction.

In systematic survey the area which is selected for the study is marked out with regular grids and walks back and forth across the grid. Any findings whether artifacts or surface features are recorded in proper reference to the grid and plotted in a master-plan to understand the overall distribution of the artifacts. Distribution of artifacts like stone tools, potsherds, debris may suggest the activities of human in the past. Beside collection of artifacts a surveyor map the position of the site and record the information in standardized forms. The artifacts collected from the lines are kept in plastic bags marked with the line and segment number. Sometimes artifacts are not collected, these are recorded in situ position. Transects are the sampling method

Sampling in archeological survey involves element sampling. In this arbitrary grid samples are randomly selected over a large area and help to estimate the densities of archeological sites over a research area. Cluster sampling governs a survey made up of arbitrary survey units. A sample unit may contain a cluster of elements, artifacts or features and use to generalize a larger region under study. The information of the sites are recorded on the basis of geographical and political location of the site, map coordinates, geology, soil composition, topography, land use, present use and owner of the site, date and time.

There are some alternative techniques to field walking though they are more destructive. Such as Shovel pit testing used in wood, garden and pasture where field walking is not possible; Coring is done to get a picture of sub soil with environment in correlation with artifactual remains; Probing is used to find the underground buried feature with a rod driving into the ground.

Fig 2: Field walking

(Source: www.penn.museum)

4.3.    Aerial Survey

There  are  two  types  of  aerial  survey-  Aerial  photography  and  Nonphotographic  method.

Nonphotographic method includes Aircraft-borne Sensor Imagery and Satellite Sensor Imagery.

4.3.1.    Aerial photography

Aerial photography is the earliest remote sensing tool used for finding archeological sites. This technique was recognized as important for archeological exploration since the First World War. Aerial photography gives a bird’s-eye view of a site. Photographs are taken from many directions at different times of the day. Photographs are taken obliquely or vertically. Aerial photographs are generally taken with black and white panchromatic film. Aerial photographs give overall view, new features, boundaries and farming settlements.

Archaeological sites are identified with the help of ‘shadow sites’, ‘soil marks’, ‘crop marks’ found in aerial photographs. The elevation, pits or ditches, eroded lands, underground structure can be identified from shadow marks.

Shadow site: When the sites can be photographed during the rising and setting of sun the long shadow indicated the relief of almost disappeared banks and ditches. This is called shadow sites.

Soils marks are only found in area where there is no vegetation. Character and colour of soil indicates different types of human activity. Such as red or black colour indicates burning, black or grey colour indicate human habitation.

Crop marks are produced due to different speed of crop growth. The crops which have deeper roots get more nutrients and grow rapidly produced positive crop marks. While the crops get fewer nutrients when there is any underground structure. In this case the roots cannot reach deeper into the soil and produce negative crop mark.

E.g. In Britain each cultural period is recognizable with different shadow mark, soil mark and crop mark. Round dark circles represent round barrows and rectangular ditches belong to Roman structure.

4.3.2. Aircraft and Satellite Imagery

Aircraft-borne instruments are used to record images of the electromagnetic radiation that is emitted from the earth surface. Archeologists use the sensor system that can be penetrated in the dense forest. Sideways-Looking Airborne Radar (SLAR) is the best known source of aircraft-borne sensor.

Satellite sensor imagery is also used to locate the archeological site. This technique senses the landscape to either side of aircraft track by sending out long pulses of electromagnetic radiation. Black-and-white and colour infrared films were used to know the archaeological features indicated by shadow of a large mound or building and irregular grids of gray lines near a major site. It helps to identify many changes in topography and disturbed sub soil. Ancient Maya civilization under forest cover was explored by this technique.

Satellite sensor Imagery is well known for the military application but it is also valuable for observing of environment. So this imagery is also helpful to explore new archaeological sites. LANDSAT series are the best known satellite series that can scan the earth and detect the intensity of reflected light and infrared radiation from the earth surface. The LANDSAT imagery gives an integrated view of a large region including soil, vegetation, topography etc.

4.4. Geophysical survey

An important remote sensing technique of site investigation is Geophysical surveying when there are difficulties to establish a precise location of a site from aerial photographs. It is a non-destructive method and advantageous when dealing with the finite archaeological resource. The application of geophysics in archaeology started since 1950. Geophysical survey includes resistivity surveying, magnetometer surveying, magnetic surveying and metal detector.

4.4.1. Resistivity surveying

Resistivity surveying is the most important geophysical technique. The principle is dependent on the variation in electric resistance which can be measured by electric current sent into the ground. When the electric current is passed through the ground, solid materials will resist more than soil. Underground solid structures like wall, road, and bedrock have a higher resistance than the soil. These differences help to identify the archaeological remains beneath the soil.

4.4.2. Magnetometer surveying

Next to the resistivity survey the second major geophysical technique is magnetometry which is used by field archeologists. The principle is based on the variation of earth’s magnetic field due to human activity. For example clay become magnetic due to firing and retains the direction of the magnetic field of the earth. Iron oxides are increased in the soil for general occupational activities resulting from burning and organic deposition. These can be detected with a magnetometer to identify the archeological remains. The proton magnetometer measures the absolute value of the earth’s magnetic field.

4.4.3. Metal detector

Metal detector is helpful to locate distribution of metal artifacts. The pulse induction is a more sophisticated device which gives an indication of the presence of metal objects. The soil removed is checked both by eye and metal detector. This technique is used in protohistoric and historic sites rather than prehistoric sites.

4.4.4. Ground penetrating radar (GPR)

This procedure is a recent development to find out buried sites. GPR transmits pulse of energy into the soil and bounce back into the receiver to find the depth and density of the deposits. The signals are altered by the density and position of the findings from the ground and plotted in a diagram. Sonar scanning is used to detect archeological irregularities in sea beds.

4.5.         Geochemical survey

Soil chemistry is changed due to human occupation in the landscape. All living things absorb phosphorus and when discarded is deposited as organic waste. The waste is deposited near the human activity area. One can identify the human activity area by tracing the phosphorous concentration of the area. Higher concentration of other materials like copper, lead, calcium also helps to identify the human activities.

5. Geographical Information System (GIS)

Geographical Information System incorporate the remote sensing technologies including aerial photographs, ground-penetrating radar, satellite imagery to provide integrated view of ancient landscape. GIS are computer aided system which incorporates computer aided mapping, computerized database and statistical packages to generate new information of the data. The GIS is advantageous to archeologists because it allows the manipulation of large amount of data and useful for solving complex settlement analysis problem. It is a powerful data base which can store many layers of data of a particular grid reference. It includes topography, vegetation, geology and geography as well as archeological data and can produce three dimensional topographic maps of an area.

6. Instruments used in site survey

All the tools and instruments of land survey are used in archeological surveying. Survey method is developed by introduction of Electronic Distance Measurement (EDM), Global Positioning system (GPS). The simplest form of surveying is sketch survey done by basic equipment like tapes, ranging poles, prismatic compass. In small site a layout of a baseline is used and for larger site a survey framework is used for surveying. A plane table is also used as surveying equipment in different parts of the World.

7. Surface Collection

Systematic collection of surface deposits is important to identify the nature and extent of the sites. The types of the artifacts scattered on the surface are helpful to know the cultural age as well as sub surface activities. The artifacts are collected systematically by laying a grid on the surface. This can help the investigator to identify the areas which are densely occupied and potential for excavation. Sometimes archeologists collect everything from the surface and analysis is done in laboratory. Sometimes collection is done by sampling method. The surface collection helps to understand age of the area and different periods of occupation, types of activities on the site, to locate the major structures and concentration of artifacts which are helpful to handle the further excavation project.

8. Recording of archeological sites

The recording of archeological sites has three components- written description, survey plan and photographic record. The description of an archeological site is written with survey and photographic data. Site survey record includes name of the site, surveyor, date of Survey, Organisation, Field director, survey team, type of survey, location, map reference, measurements of survey area, datum point (point of reference and control), description of location, condition, weather, owner of the site; Equipment/instrument used, methods used, control station, point, description; stratigraphic information include character of soil, nearest water source, environment and surroundings, present condition; collection of surface artifacts, collection method, artifact bag number, samples of ecofact collected; photographs, drawing, maps, observation and recommendation. Recording of the details of exploration should be documented properly for further research either excavation or exploration, otherwise the data will be lost.

Summary

Finding of archeological site is an important part of archeological research. So exploration or site survey is an important archeological method to find out new sites.

The procedures are broadly categorized into two- traditional and modern. The traditional method of field surveying is field walking, whereas modern methods include scientific technologies like remote sensing, geophysical and geochemical survey.

Field survey methods are broadly categorized into four types- Desktop study, Surface survey, Aerial survey, Geophysical survey, Geochemical survey

Desktop survey includes the study of existing documents and maps to get a primary knowledge to find out a new site. Field work is not necessary in this part.

Surface survey consisted of traditional field walking and observation. New software was introduced known as Geographical information System, which help to understand the location and the other geographical features as an indicator of a site.

The aerial survey is a bird’s-eye view of site help to identify the archeological features of a broader area and satellite images also used to find out a new site.

The geophysical survey is consisted of number of scientific techniques including resistivity surveying, magnetometer surveying, metal detector, Ground penetrating radar (GPR) and Sonar. Geophysical survey is very helpful to identify human activities in different stratigraphical layers beneath the top soil.

Geochemical survey is basically the analysis of soil. Soil types are good indicator of past human activities on the site.

So the above discussion reveals that multidisciplinary action is needed to finding as well as studying archeological sites. Data should be rechecked with previous work as because there are number of geographical, geological and human disturbances have been occurred on a site. It is a less expensive method of archeological field research.

In spite of a number of difficulties, exploration or site survey is a primary requisite to find a new site and an important part of non-destructive archeology and for further excavation.