MARYLAND GEOLOGICAL SURVEY 107 



preserved in Maryland, but the materials which composed the Calvert 

 formation in this county were deposited in seas of moderate depth in 

 which an abundance of life was present, as is shown by the remains of 

 diatoms and the extensive beds of fossil mollusks. The remains of 

 whales and other cetaceans show that these vertebrates abounded in tlie 

 ocean, and the discovery of a bone belonging to a gannet indicates that 

 birds existed along the nearby shores. This particular form doubtless 

 sought its food in the sea as the modern fishing gannets do at the present 

 time. 



The Calvert epoch was brought to a close by the elevation of the region 

 once more above the level of the ocean. A period of erosion followed 

 which was probably of short duration and closed with the depression of 

 the region again beneath the sea. Then followed the deposition of the 

 Choptank and St. Mary's formations, in which conditions similar to 

 those just described for the Calvert were repeated. 



SEDIMENTARY RECORD OF THE COLUMBIA GROUP. 



The sedimentation of the Chesapeake Group was brought to a close 

 by the elevation of the region once more above the ocean. After an 

 extensive interval of erosion, the county was again depressed beneath 

 the waves. This was the period in whirh the Tjafa3''ette deposits were 

 laid do^vn and subsequently eroded during another epoch of elevation, 

 but as none of these deposits have been found within Calvert County, 

 this particular phase of the history will not be discussed in this place. 

 The deposits which lie immediately under the formations of the Colum- 

 bia Group are those of the Chesapeake Group. 



The Sunderland, Wicomico, and Talbot formations are developed in 

 terraces lying one above the other in vertical range from tide to an alti- 

 tude of about 180 feet. Beneath these three terraces, there is forming 

 to-day a fourth which extends from high-tide downwards. 



The key to their interpretation is secured by studying the manner in 

 which this recent terrace is forming. At the present time the waves of 

 the Atlantic Ocean and Chesapeake Bay are engaged in tearing away 

 the land along their shores and in depositing the detritus on a submarine 



