MARYLAND GEOLOGICAL SURVEY 91 



THE WICOMICO FORMATION. 



The next younger formation of the Columbia Group is the Wicomico. 

 It lias received its name from the Wicomico Eiver in Charles and St. 

 Mary's counties, for in the valley of this estuary it is found well de- 

 veloped. Like the Sunderland, it consists of clay, loam, sand, gravel, 

 and ice-borne boulders ■which -were deposited by the waters of Chesapeake 

 Bay and its estuaries. Since its deposition it has suflEered considerably 

 from erosion. 



Areal Distribution. 



The Wicomico formation is not as extensively developed in St. Jlary's 

 County as its predecessor, the Sunderland. It is developed as a terrace, 

 occupies a lower level and wraps about the margin of the Sunderland 

 formation like a border. The formation can be best seen in the valleys 

 of the Patuxent and Potomac rivers, and also in gorges of the larger 

 estuaries tributary to the latter. Among these can be mentioned Wi- 

 comico and St. Mary's rivers, and St. Clement and Breton Bays. Ex- 

 tensive areas of the Wicomico formation are also found in the higher 

 valleys of streams emptying into these estuaries and along the eastern 

 margin of St. Mary's County facing Chesapeake Bay. 



Many streams have forced their headwaters back into the body of 

 the Wicomico formation, so that it no longer is as continuous as when 

 first deposited, but has developed a sinuous outline and is broken into 

 a number of isolated areas. 



Structure and Thickness. 

 The base of the Wicomico formation is so extensively covered with the 

 Talbot formation which wraps about it that it is difficidt to determine 

 the attitude of the former by comparing the various heights at which 

 its base is found to rest. A much more accurate conception may be 

 secured by comparing the altitude of its surface in various places. In 

 the northern part of the county the surface of the Wicomico formation, 

 where it abuts against the margin of the Sunderland, rests at about 100 

 feet, while at Eidge, under similar conditions, it has an altitude of about 



