298 ELEMENTARY GEOLOGY 
These are very often, indeed usually, river valleys 
which were formed above the water, but have been 
partially drowned by a change in the level of the land, 
allowing the water to enter the valleys. Such a coast 
as that of Maine (Plate 13), and indeed of all New 
England, furnishes abundant illustration of this class 
of evidence of land submergence. So also do the 
valleys of the St. 
Lawrence and the 
Hudson, as well as 
Delaware and Ches- 
apeake bays on the 
eastern coast, while 
San Francisco harbor, 
and the irregular 
Trunk of a tree on a beach at Cape Ann, Mass. coast line of Wash- 
Standing where it grew, but now nearly at ington and. British 
low tide mark. 
Fic. 176. 
Columbia on _ the 
western coast, and the irregular eastern boundary of 
northern Europe are due to the same cause. 
Changes of Level nm New England. On the New 
England coast there are registered a series of changes 
of level in recent geological times. We know well that 
the land was formerly much higher than at present, 
and that river valleys were then carved in the rocks. 
Then the New England region was submerged to a 
level below the present coast line; and at this period 
