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

This map shows the distribution and thickness of material overlying 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 material overlying the principal clay unit commonly consists of sand.  In places this sand is overlain by gravel or sand and gravel, and may also be overlain by fine materials not related to the principal clay unit.

Locally the actual thickness of material overlying the principal clay unit may differ from the mapper value because the clay grades upward into the overlying material.  The contact in these areas is poorly defined and is an estimate.