Ground Stone Tools and Experimental Archaeology
Ground stone tools are a class of object which are defined by the techniques used in their manufacture. These techniques can be summarised as pecking, grinding, drilling, cutting, faceting, graving and polishing. They are global phenomenon, not confined to any region, and thus the techniques described above are generally evident where-ever they appear in the archaeological record. Like flint tools, they represent a durable record of mankind’s adoption of technology. They are associated with later prehistory, especially the Neolithic, though there are examples from Mesolithic contexts. In all instances there is an increased use of them following the adoption of agriculture by society. In many cases their use continued (and in some cases increased, after the advent of metallurgy) before they fall from use, generally in the later Bronze Age. Many of these tools appear to have evolved in relation to particular technical problems with pre-existing tool types. Given they are a global phenomenon lasting many thousands of years where-ever they occur, they are an important aspect of prehistoric archaeology world-wide.
The key point to bear in mind are that ground stone tools (or implements) represent a change in the way mineral types were exploited by prehistoric societies. Previously, crypto-crystalline rocks were the main mineral types exploited by man. In Britain, Grimes Graves in Norfolk and the in Scotland represent the greatest sources of flint materials. The technologies associated with ground stone tools allowed people to utilise other rock types, because the techniques could be used to shape any type of rock. Even the hardest rocks (granites, nephrite, and jadeites) can be shaped using the same basic techniques described above. This may have had profound social implications as the control of minerals with relatively limited distribution patterns was broken – suitable materials for use with ground stone tool technology can be found more or less anywhere – there is a huge diversity in the rock-types pressed-into service.
Whilst flaked tool (flint) technology is relatively well-covered in the literature (Andrefsky 1998, Keeley 1980, Schick & Toth 1993 and Whittaker 2003 for example), there is a dearth of similar material for ground stone tools. Almost invariably they are discussed from an entirely theoretical perspective (Ashmore 1996, Bradley R. 1998, Edmonds 1992; 1995; 2004, Hodges 2000, Malone 2001, Pearson 1994, Pollard 2002, Ritchie 1995, Woodward 2000). Interpretations are based on theoretical hypotheses which are untested. These abstract models are used to substantiate a number of contestable issues ranging from social status, labour investment, function, use and utility, to sepulchral roles.
How were ground stone implements manufactured? Before work can begin on any project, suitable raw material has to be collected. This is stage one in the manufactory process, and is extremely important. Certain types of raw material were exploited to the exclusion of others. Generally this relates to the mechanical qualities of the rock – its hardness, grain-size, flexibility and durability. These appear to have been more important than the difficulty of working any particular material. Granites were often used – representing one of the hardest-known substances in the prehistoric world. Prehistoric people were expert in selecting particular rock-types. They could recognise those types which were most suitable for manufacture. This involves a considerable knowledge of the qualities of rock types. Colour, texture and friability are the keys to recognising rock-types.
Procurement strategies often involved the extraction of large quantities of minerals from a particular source. The extent to which this is true can be seen in the Langdale valley in the English Lake District, where one of the workings has created over 750 metres of debitage (South Scree), in places several metres deep. And that is just one of many extraction points in that valley. The total amount of rock quarried runs into hundreds of thousands of tons. Of course, much of this is still in situ, in the form of debitage. But the fact that people went to such lengths to obtain a particular raw material speaks volumes about its significance and its value as a commodity. In other instances, we see riverine cobbles or beach cobbles being exploited. The famous Bush Barrow mace-head, for example, is made from the distinctive Flecked Devon Limestone, and which was probably obtained from Devon’s beaches, just as it can be found at places like Dawlish today.
Having located a suitable supply of rock, the next stage in the manufacturing process was roughing out. Many rock-types can be chipped. They do not have good conchoidal fracture, but still, the same techniques used in flint-knapping can be used to quarter rocks and create a rough-out. In other cases, where rocks possess no or extremely poor conchoidal fracture, a second technique (pecking) has to be used.
In any case, it appears that usually some roughing-out was done at the source, and debitage is a feature of such sites. Langdale tuf, as described above, is a case in point. After a rough-out has been obtained, further shaping is done using the pecking method. Here a hard hammerstone (often flint, but sometimes other very tough rocks such as granites or certain types of sandstone) was used to repeatedly peck-away at the surface of the implement, slowly creating the desired shape. Following this, another technique would be used – grinding. Generally grinding took place on a granular polissoir – a flat rock with good abrasive qualities. In Britain, high-quartzite sandstones are fairly common and sandstone polissoirs are excellent for shaping tools. In other cases, where less abrasive polissoirs were available only, quartz sand can be introduced as an abrasive. Water is added to remove the extremely fine residue created during the grinding process. If this is not removed, the granular texture of the polissoir is compromised resulting in a less efficient grinding rate.
Grinding is a slow process. It is strenuous to the extent that muscle fatigue occurs after prolonged periods (say a couple of hours), but there is every likelihood that this work was done intermittently. Ethnographic examples indicate that this indeed was often the case in different parts of the world. The harder materials (camptonite, granite, some types of marble, nephrite and jadeite) are particularly resistant to grinding and there is evidence from New Zealand that some implements might be worked on over a period of months or even years… depending upon their function (generally, working tools were produced more rapidly than objects with high status).
After grinding, implements were sometimes further embellished. This could be achieved through graving (carving lines on the surface of the tool), or reticulation (small symmetrical grooves cut into the rock). Many ground stone implements were hafted by means of a shaft-hole. This was drilled through the body of the implement so that it could be attached to a wooden haft. Sometimes drilling was done from one side only, resulting in a cylindrical shaft-hole, and at other times it was done from both side (initially through pecking) which creates a distinctive ‘hour-glass’ shape shaft-hole.
Finishing might take the form of polishing. A very fine abrasive (such silt or the residue obtained from the grinding process) could be applied with a leather pad in a circular motion to create a high-gloss finish.
It is generally assumed that those objects which probably took the longest to manufacture represent high-status items. However, very little research has been done to determine labour investment models for many types of object, and some of the suggested models are plainly inaccurate. A simple carpentry tool such as a ground flint adze might have taken as long to make as an elaborate battle-axe. In the extant literature, a battle-axe is ascribed with high-status, whereas the humble adze is deemed to be merely a carpentry tool. One of the problems with interpreting ground stone tools is that modern aesthetics are misleading – sometimes the most elaborate-looking objects were less time-consuming to manufacture. A post-modern western perspective (high labour-investment means high value) might not apply to prehistoric implements.