At about 10500 B.P. a large slab of sandstone was detached from the face of a sandstone cliff on the side of a hill. At the time this occurred the cliff face was probably buried under a variety of glacial and proglacial deposits, possibly including till, and definitely including glacial lake sediments. When the slab was detached from the bedrock it moved about three meters away from the bedrock face, but remained in a vertical position. Consequently, this created a gully with vertical sides running parallel to the hillside. The floor of the gully sloped steeply south, conforming to the slope of the hillside, and was littered with sandstone boulders and crushed sandstone left behind as the slab moved downhill. Upslope from this gully the hillside was mantled in glaciolacustrine sediments. Over a period of about 1000 years these were redeposited in the gully, forming a layer of variable thickness over the boulders on the floor. Because the gully floor sloped to the south, the greatest thickness of redeposited glaciolacustrine sediments was deposited against the upslope side of the detached slab, on the south (or downslope) side of the gully. Here up to a meter of sediment accumulated in about 1000 years . By about 9500 B.P. the rate of deposition had slowed sufficiently to allow soil horizons to form, and the subsequent history of deposition is a mixture of allochthonous slopewash and autochthonous weathered sandstone, with numerous soil horizons.
STRATIGRAPHY AND DATING more -->
The site's stratigraphy is complex, and numerous layers in the lower portion of the site can be resolved into a series of stratigraphic zones. The lowest boulders form Zone I, and this zone contains no artifacts or fauna. The redeposited glaciolacustrine sediments are Zone II. After the 1983 excavations this was divided into two subones; as a result of the 1991 field season, we now recognise four subzones. The initiation of soil horizons marks the beginning of Zone III. In this paper, we are concerned only with the lowest part of Zone III, which is termed Subzone IIIa.
Radiocarbon dating places Subzones IIa and IIb between 10,500 and 10,000 B.P. Zones IIc and IId date from 10,000 to slightly before 9500 B.P. Zone IIIa has a single date of about 9500 B.P. More detailed discussion of the stratigraphy is contained in Handly (1993) and Driver et al. (in press).
