122 THE GEOLOGY OF PEINCE GEOKGE's COUNTY 



Character of Materials. — The materials which constitute the 

 Wicomico formation are similar to those found in the Sunderland — ■ 

 in fact, many of them have been derived from that formation. They 

 consist of clay, peat, sand, gravel, and ice-borne boulders. The dis- 

 tribution of these materials is similar to that of those in the Sunder- 

 land in that they grade one into another both vertically and hori- 

 zontall}^, the coarser materials preponderating at the base of the for- 

 mation and the finer materials toward the top. At some places the 

 materials are very much decayed, as in the Sunderland. 



In the Potomac Valley near Washington boulders carrying glacial 

 striae have been found in the Wicomico formation. The great size 

 of these boulders and their occurrence with much finer materials 

 furnish evidence of their transportation by floating ice. 



The amount of loam present in the Wicomico is exceedingly vari- 

 able. Wherever the loam cap is well developed the roads are very 

 firm and the land is suitable for the production of grass and grain ; 

 but where the loam is present in small quantities or absent altogether 

 the roads are apt to be sandy. 



Physiographic Expression.- — The Wicomico formation is developed 

 in a terrace which is described in the section headed "Topographic 

 features" as the Wicomico plain. This plain. is sej)arated from the 

 Sunderland terrace, which lies above it, by a scarp, usually above 20 

 feet in height, which is one of the most constant and striking to- 

 pographic features in the region. The Wicomico j^lain is in turn 

 in most places separated by an escarpment from the Talbot terrace, 

 which wraps around it at a lower elevation. From the Sunderland- 

 Wicomico escarpment the surface of the Wicomico formation slopes 

 away gently toward the surrounding waters in the manner of a wave- 

 built terrace. In the northern portion of the county the surface of 

 the Wicomico, at the base of this escarpment, lies at an elevation of 

 about 100 feet, while in the southern portion the elevation of the 

 corresponding surface is about 90 or 95 feet, indicating a very gentle 

 slope toward the southeast. Since the Wicomico was deposited it 

 has been subjected to considerable erosion and its originally level 

 surface has been transformed, at least along the waterway's, into a 

 gently rolling one. 



