|The Calvert Cliffs on the western shore of the Chesapeake Bay in Calvert County between Chesapeake Beach and Drum Point|
Miocene (5.3 - 23.7 mya) exposure of olive-gray silt/clay of the St. Mary's, Choptank, and Calvert Formations. Fossil remains of animals that lived on the ocean floor, or died and settled, are preserved with the deposits from the Coastal Plain and crystalline rocks of the Piedmont region. These deposits are now exposed in cliffs up to 100 feet high, and as the wind and water erode the cliffs, new fossils are exposed and return to the Chesapeake Bay once more. The Chesapeake Group is divided into three formations. The youngest deposits belong to the St. Marys Formation, which is exposed at Little Cove Point, consists of bluish sandy clay and fine sandstone. Beneath it is the yellowish sand and greenish clay and marl of the Choptank formation. The oldest, the Calvert Formation, is composed of diatomaceous earth and dark sandy clays and marl.
Strata of the Calvert Cliffs are many times referred to as "zones" (Shattuck's zones) thanks to George Burbank Shattuck who published the first comprehensive studies of the stratigraphy of the Chesapeake Bay area. Today, his zones are still in use, although they do not correspond to proper stratigraphic zones. Refer to this webpage for additional information on Shattuck's zones http://mywebpages.comcast.net/browniebeach/shattuck.html
A photo display of the fossil bearing counties of Maryland
Thanks to the Maryland Geological Survey