Map showing thickness of principal clay unit, Hartford South Quadrangle, Connecticut

This map show the distribution and thickness of the principal clay unit.  The clay unit consists of a thick, massive bed of relatively pure clay in some areas; in other areas it consists of discrete layers of clay alternating with layers of silt and very fine sand (varved clay).  The upper layers of the clay unit commonly grade into a layer of silt and very fine sand.  Small, isolated clay deposits not associated with the principal clay unit are not mapped.