Refitting Megaliths in Western France
Mens, Emmanuel, Antiquity
The Armorican bedrock of western France has been used since the Neolithic to make megalithic structures. Each of the menhirs, orthostats and capstones extracted from granite outcrops has a specific shape, marked by a slightly curved weathered face and an opposite face that is relatively flat. Noting the flat quarrying planes and the curved weathered faces enables us to propose the relative location of each block within the outcrop before its extraction. By means of a typology of forms, the megalithic blocks can be mentally positioned in the upper or lower levels of the outcrop in the same way that flint flakes can be repositioned in a core. Accordingly, the term core outcrop can be justified to denote the original rock formation and I use the expression mental refitting for the process of replacing the blocks notionally in their original locations. The refitting reveals the successive stages in the working of the outcrop and the order in which the blocks were extracted. This method opens up a new field of research on the deployment of megalithic raw material during the Neolithic period.
Outcrops for monumental structures
The area between the Loire estuary and the Gulf of Morbihan (Figure 1) has many granite outcrops, as do other areas of Europe (Dehn et al. 1991). Most of them are of modest dimensions, but some examples rise to several metres tall. These rocks, rounded by weathering, usually display a well-oriented texture and were a raw material of first choice for the builders of megalithic monuments. In places such as Carnac, the Neolithic builders made intensive use of these outcrops to construct alignments of standing stones, to such an extent that the stock of stone available above ground has been depleted, and the geography of the area has been permanently modified.
[FIGURE 1 OMITTED]
The extraction of the blocks was probably greatly facilitated by the natural cleavage planes of the granite (Gaume 1992). Like all stones of magmatic origin, granites have networks of fractures known as joints. These discontinuities in the bedrock divide the stone into roughly quadrilateral blocks and are potential lines of weakness that may be exploited. Two kinds of joints are regularly observed in the area of the Loire estuary and Gulf of Morbihan, the first horizontal, the second vertical. This orthogonal arrangement of joint networks is not universal, however, and some joints are curved in shape or have a sub-vertical or sub-horizontal orientation. Nevertheless, granite has a strong tendency to fracture along orthogonal planes, and this allows us to develop a theoretical schema for the different ways in which blocks could have been extracted.
Weathered face and fresh face
A megalithic block coming from an outcrop usually displays two main faces:
* the 'fresh face', which is almost flat and corresponds to the surface where the stone was broken away from the outcrop; and
* the 'weathered face', the convex side of the stone that was initially exposed to the open air.
As a result of erosion, weathered faces usually display a typical rounded shape, which facilitates their identification (Giot et al. 1979). Nevertheless, distinguishing them from fresh faces can be difficult if the convexity is slight. But a closer inspection of the exposed face reveals traces of erosion that geographers have called 'micromodeles' (Godard 1977) and are the result of agencies such as wind, rain, heat, ice, salt and vegetation. These erosion stigmata can take the form of basins or grooves that are highly reliable indicators for identifying ancient weathered surfaces. At Carnac, D. Sellier (1991; 1995) has defined two specific categories of 'micromodeles':
* pre-megalithic, meaning that erosion occurred before extraction; and
* post-megalithic, meaning that erosion occurred after erection.
These 'micromodeles' can be used to distinguish the weathered from the fresh (or quarried) faces of the megalithic blocks. …