GENERAL STRUCTURE OF THE COASTAL PLAIN. 



435 



burg it is overlapped by succeeding formations, and only appears in the 

 larger depressions toward the head of tide-water. 



The Severn formation lies on the irregular surface of Potomac sands or 

 clays, and thins out and disappears a short distance south of Washington. 

 Opposite Washington its edge is locally cut off by the overlap of succeeding 

 formations. 



. The Pamunkey formation lies on a slightly irregular surface of the 

 Severn formation in Maryland and directly on the Potomac sands southward 

 through Virginia. Opposite Washington its western edge is also cut off 

 locally by the next succeeding formation, and for the greater part of its area 

 above tide-level it is so deeply buried under later deposits that it only 

 appears in the deeper depressions. 



SecCion 2. Soulh of Baltimore 



>>''rffS#a;S^. 



Section 3. Through Wa»hiDgtoD D C. 



Section 4 Througb Alexandria V£ 



Section 5 fredericksburg regii 



Section 6 Through Richmond 



APPOMATTOX |;;;);;;,1 



CHtSAPLAKE 



PAMUNKE.Y 



SELVtRN 



POTOMAC 



CRYSTALIINLS p^-li' 



("Horizontal lOmilesOin. 

 '^"'^^ Ivertioal 2000 feet nn. 



Figure 1— Sections through the Cenozoic and Mesozoic Formations and the Crystalline Rocks of eastern 



Virginia and central Maryland. 



The Chesapeake formation rises above tide-level for nearly the entire area of 

 the coastal plain region. It lies on a gently eastward dipping plane of un- 

 conformity on the Pamunkey formation, but overlaps westward to the 

 Potomac formation at Washington, and to a greater or less degree to the 

 crystalline rocks in the region southward from Fredericksburg into the 

 Carolinas. 



The Appomattox formation is a wide-spread, high-level terrace capping, 

 which lies upon and overlaps all of the other formations. Southward- from 

 Fredericksburg it is an almost continuous cap on the high lands from the 



