THE QUATERNARY PERIOD 463 



remains of the extinct animals of the glacial times. There is, 

 however, no proof that he was not then on the scene. 



THE RECENT EPOCH 



Little change since the glaciers passed away. By the 

 departure of the last ice sheet northern North America was 

 left in very much its present condition. Streams have cut 

 small valleys in the glacial drift, many lakes have been filled 

 by the accumulation of silt and vegetable matter, and some 

 have been drained; but aside from such minor changes the 

 aspect given the land by the glaciers has been preserved 

 through the few thousands of years which have elapsed since 

 the ice retreated. 



The Champlain submergence. About the shores of 

 Lakes Champlain and Ontario marine shells and the bones of 

 whales have been discovered in beds of clay high above the 

 present lakes. In order that the sea should have extended in 

 so far, the land must have been several hundred feet lower 

 than now. At this time the salt water probably spread up 

 the Hudson River to Lake Champlain, and also up many 

 other valleys in the East. That changes of level are still in 

 progress is known from the fact that old beaches all along the 

 Great Lakes are no longer level, as of course they must have 

 been when made. In general, they are now higher on the 

 north and northeast and are tilted south west ward. Those of 

 Lake Superior gradually sink from an elevation of four hun- 

 dred feet at the east end of the lake to lake level and even 

 pass beneath the water before reaching Duluth. 



Other slight risings and sinkings of the land have been in 

 progress recently in many parts of the world. Indeed, there 

 is scarcely a coast anywhere which does not reveal either 

 raised beaches and sea-cut cliffs, or else drowned valleys 

 and archipelagos. The former are conspicuous at many 

 points in California and Alaska, while the latter are especially 

 characteristic of the Atlantic coast of Maine and Britain. 



