16 PIIYSIOGEAPHY AND GEOLOGY OF THE COASTAL PLAIX PROVIXCE. 



merged valleys of streams carved out during the time when the region stood 

 at a higher level than at present. Chesapeake Bay, which is the old valley 

 of the Susquehanna Eiver, and Delaware Bay, which is the extended valley 

 of the Delaware Eiver, together with such tributary streams as the Patuxent, 

 Potomac, York, and James rivers are examples of such bays and estuaries, of 

 which there are many others of less importance. The streams which have 

 their sources in regions to the westward are almost invariably turned in a 

 direction roughly parallel to the strike of the formations as they pass out 

 into the Coastal Plain. This is well shown in the case of the Potomac and 

 James rivers which at Washington and Eichmond suddenly change their 

 courses and flow in an almost southerly direction for several miles. With 

 this exception the structure of the formations and the character of the 

 materials have had little effect upon stream development except locally. 



The materials of which the Coastal Plain is composed consist of boulders, 

 pebbles, sand, clay, and marl, mostly loose or locally indurated. In age 

 the formations range from Lower Cretaceous to Eecent. Since the time 

 when the oldest formations of the province were formed there have been 

 many periods of deposition alternating with erosion intervals. The sea, 

 however, advanced and retreated differently in various parts of the region, 

 so that at the present time few of the formations can be traced by outcrop- 

 ping beds throughout the entire area. Different conditions thus prevailed 

 and great variability in tlie deposits has been produced during each period. 



The Virginia Coastal Plain occupies the eastern portion of the State and 

 has an area of somewhat more than 14,000 square miles, of which about 

 10,000 square miles belong to the subaerial division or Coastal Plain proper, 

 and about 4,000 square miles to the submarine division. In the former are 

 also included the estuarine waters of the lower Chesapeake Bay with the 

 tributaries of the Eappahannock, York, James, and other rivers, which 

 together have an area of about 3,000 square miles. The Coastal Plain proper 

 forms about one-fourth of the entire area of the State. On account of the 

 tidal bays and estuaries which traverse it in all directions it has received the 

 name of "tide-water Virginia" and its nearly 3,000 miles of shore-line is 

 bordered at almost all points by navigable waters. 



To the north and south the Coastal Plain of Virginia is continuous with 

 the Coastal Plain regions of Maryland and North Carolina ; to the east the 

 region is bounded by the basin of the Atlantic Ocean; and to the west a 

 much more irregular and less easily determined line separates it from the 

 Piedmont Plateau. The difficulty in drawing the westward limiting line is 

 due to the relations existing between the formations of the two regions, the 



