DATING KEZAR LAKE PICTOGRAMS.

Pictograms painted on gneiss near the inlet of Great Brook into the north-western corner of Kezar Lake are covered and partly obscured by a thin white hydrated amorphous silica film. Detailed studies of the rock surface at one place on the cliff reveal two episodes of painting separated by an interval of time during which silica was deposited over the lower image. The basal red haematitc paint layer follows the topography of the rock surface and therefore appears to have been painted directly on the rock. A layer of white amorphous silica, approximately 0.05 mm thick, was then deposited naturally from seepage water that flowed over the painting before a second haematite figure was painted. A similar white film covers and masks the details of the second figure. On-site microexcavations were carried out to obtain powdered silica samples from which carbon, derived from fossilised micro-organisms trapped in the coating during silica precipitation, was extracted for accelerator mass spectrometry radiocarbon dating of the ages of the pictograms. [ABSTRACT FROM AUTHOR]