THE WICOMICO FORMATION. 183 



distinctive. A more careful search of the Sunderkind deposits of Virginia 

 will undoubtedly show similar plant remains, for plant life must have 

 existed in the region of deposition as shown by the dark color of some of the 

 clays which is evidently due to carbonaceous matter in a finely disseminated 

 condition. 



Area! distribution. — The distribution of the formation is co-extensive 

 with that of the Sunderland terrace already described as forming the upland 

 divides between the major streams in a belt extending from Westmoreland 

 to Southhampton counties. The formation except over the broader divides is 

 greatly dissected, and the normal plain-like character of the Sunderland 

 surface is frequently wanting. Since its deposition it has suffered much 

 more erosion, than either of the two younger formations, but enough of the 

 surface still remains to establish its identity over an extensive area. 



The Wicomico Formation. 



Name. — The Wicomico formation receives its name from the Wicomico 

 River which enters the Potomac from the Maryland side between Charles 

 and St. Mary's counties. 



Lithologic character. — The materials which constitute the Wicomico for- 

 mation are similar to those found in the Sunderland, and in fact, many of 

 them have doubtless been derived from that formation. As stated on a pre- 

 vious page, it would be impossible to distinguish between the Pleistocene 

 formations on the basis of lithologic differences. The criterion of position is 

 the only accurate method of discrimination. The deposits consist of clay, 

 sand, gravel, and ice-borne boulders which grade into each other both ver- 

 tically and horizontally. It is noticeable, however, as in the case of the 

 Sunderland, that there is a preponderance of the coarser materials at the 

 base of the formation, wliile tlie finer materials are largely developed toward 

 the top. Decayed pebbles of the Piedmont crystalline rocks and Paleozoic 

 fossil-bearing pebbles from the Appalachian region are frequently found in 

 the gravel beds or are irregularly distributed in the sands and clays. 



In the Potomac valley near Washington, boulders carrying glacial striae 

 liave been found in the Wicomico formation. The great size of the boulders 

 and their occurrence with much finer materials furnish the evidence of their 

 transportation l)y floating ice. Tbe amount of loam present in the 

 Wicomico is exceedingly variable. Wherever the loam cap is well-devel- 

 oped the roads are very firm and the land is suitable for the production 

 of grass and grain, but in those regions where the loam is present in small 



