MINERALOGY OF CERAMIC PERIOD POTTERY FROM FOUR SITES IN CASCO BAY, MAINE

Ceramic period pottery from the Great Diamond Island, Harriman, Pettingill and Basin sites are controlled by 23 radiocarbon dates which demonstrates that the sites were active between 1000 B.C. and 1600 A.D. The sites variously are interpreted to represent late summer and early winter occupations and include a combination of early, middle and late ceramic period pottery styles. Pottery from these sites consist of two grain size fractions. Open pit firing of the vessels at relatively low temperatures has produced a vessel that is texturally analogous to a moderately consolidated sand-rich mudstone. The vessels can be treated in terms of their “matrix” or paste and their “framework” or temper. The majority of the material in the vessels is matrix which falls into the clay with minor silt size categories. Interspersed in the matrix are medium to very coarse sand – sized grains. The matrix portion of the vessels was most probably collected from prominent bluffs of glacial marine clays assigned to the Presumpscot Formation. Many of these bluffs are Holocene erosional features, and they occur throughout the Casco Bay area. The sand-sized grains providing the temper component were collected from sands produced by the weathering of local schists and pegmatites. Ultrasound techniques effectively disaggregate the vessels back into their original, clay, silt and sand - sized consitutents. X-ray diffraction analysis of the clay and silt - sized portion demonstrates that the finer grained portion has a variable mineralogy that largely consists of differing proportions of quartz, albitic plagioclase, microcline, orthoclase, muscovite, phengitic and illitic phyllosilicates and chlorite. Thin sections demonstrate that the sand-sized (temper) component consists of both undulatory and non-undulatory quartz, microcline and oligoclase, plus composite grains consistent with granite pegmatite, biotite granite, sillimanite - quartz schist, calcsilicate and quartzite. Less commonly the temper consists of soft shell clams or coarse – grained muscovite. Variations in paste and temper suggest that manufacturing of the vessels was not limited to a single locale, but occurred at several sites throughout the greater Casco Bay area.