Gray to grayish-brown, clayey silt to silty clay interbedded
with gray to light-gray silty to fine to coarse quartz sands.
Discontinuous beds of shell are common in the sands and in the
clayey silts. Found in the subsurface throughout Kent County.
Interpreted to be a marine deposit. Rarely the surficial unit on
the uplands in northwestern Kent County where the Columbia or
Beaverdam Formations are absent. Outcrops are patchy and are too
small to be shown on this map. Three major aquifers are found
within the Calvert Formation in Kent County: the Frederica,
Federalsburg, and Cheswold, from top to bottom, respectively
(McLaughlin and Velez, 2006). Ranges up to 425 feet thick. Light
gray to blue gray, fine to medium, shelly, silty, quartz sand
and clayey silt. Discontinuous beds of fine sand and medium to
coarse quartz sand are common. Base of the unit is marked by a
coarse to granule sand that fines upwards to a medium to fine
silty sand. This sand is the Milford aquifer (Ramsey, 1997;
McLaughlin and Velez, 2006