176 



GEOLOGY 



the streams of the Appalachian Mountains that there is probably 

 no considerable stream in the whole system which has not gained 

 or lost through its own or its neighbor's piracy. 



Sinking. The land on which a river system is developed may 

 be depressed relative to sea-level. In this case the sea occupies 



Fig. 144 



Fig. 145 



Fig. 144. Chesapeake Bay and its surroundings. The bay is a drowned 



river valley, and the lower ends of its tributary valleys are also drowned. 



Fig. 145. The drainage of the region about Cheaspeake Bay as it would 



have been but for drowning. 



the lower ends of valleys, converting them into bays and estua- 

 ries. A valley in this condition is said to be drowned. Of drowned 

 valleys there are many examples along the Atlantic coast. Thus 

 the St. Lawrence is drowned up to Montreal, and the Hudson up 

 to Albany. If the drowned portion of the latter valley were not 

 so narrow, it would be a bay. Delaware and Chesapeake bays, 

 as well as many smaller ones, both north and south, are likewise 

 the drowned ends of river valleys (Figs. 144 and 145). 



