54 PHYSIOGRAPHY AXD GEOLOGY" OF THE COASTAL PLAIN PROVINCE. 



belt along the "fall-line" seem to resist stream erosion less than an}' of the 

 other Coastal Plain formations. As a result the streams on entering the 

 Coastal Plain province follow the outcrop of these beds for several miles. 

 The best exposures of the Potomac beds are found along the Potomac, 

 Eappahannock, North Anna, and James rivers in that portion of their 

 courses where they flow in a southerly direction. The same conditions 

 appear on the Appomattox Eiver below Petersburg and in the Nottoway 

 Eiver in Sussex County except that these streams flow northward on the same 

 beds, possibly due to an initial northerly slope in this portion of the Coastal 

 Plain area. The Chickahominy agrees with the streams first mentioned 

 above in flowing in a southerly course for several miles on reaching the 

 Coastal Plain. Thus far the Potomac beds have not been observed along 

 this part of the Chickahominy, but it is not improbable that they are there 

 present but concealed from view by the more recent deposits whicli fill the 

 valley. 



Tide-n-afir esluarics. — The most prominent features of the <lrainage of 

 Virginia are the broad tidal estuaries which penetrate the State to the 

 "fall-line" and divide the Coastal Plain region into a series of long, narrow 

 peninsulas. These deep tidal streams have always contributed to the natural 

 wealth of the State through the water products — oysters, crabs, and fish-- 

 which they have yielded in such great quantities, and also through the easy 

 transportation which they -have afforded for the products both of land and 

 sea. When water transportation was practically the only means of convey- 

 ance the importance of these navigable streams was much greater than at 

 present and for that reason tide-water Virginia was first brought under 

 cultivation and during the 17th and 18th centuries was the leading section 

 of the State. Foremost in importance among these bodies of water is Chesa- 

 peake Bay, while tributary to it are the long estuaries of the Potomac, 

 Rappahannock, and James, between 150 and 200 miles in length and the 

 shorter ones of the York, Wicomico, Piankatank. and Nansemond rivers and 

 Mobjack Bay, besides hundreds of others of lesser importance. These all 

 represent ancient valleys cut by streams when the country stood at a higher 

 level than at present and which have been converted into their present condi- 

 tion by a depression of the country which permitted the waters of the sea 

 to enter their valleys. In most of these estuaries the position of the former 

 streams can be determined by the deeper channels but in some cases these 

 have been obliterated by the deposits which have been laia down m then, 

 since their submergence. As little erosion takes place below tide level, it is 

 possible to gain some idea of the amount of subsidence which has given rise 



