CENOZOIC ERA. AGE OF MAMMALS. 



391 



the level in the Ohamplain period. In southern New 

 England it is 50 feet high, in Maine 100 feet high,, on 

 the Gulf of St. Lawrence and Labrador 500 feet, and 

 in Greenland 1,000 feet high. The old sea-line may 

 be traced on both sides of the St. Lawrence Eiver, and 

 thence around Lake Champlain nearly 500 feet high, 

 showing that there was a wide bay or sound in this re- 

 gion. It is this which gives name to the epoch. On 

 the bench marking the sea-level about Lake Champlain 

 have been found not only many marine shells, but also 

 the skeleton of a stranded whale. 



Lake-Margins. About all the Great Lakes are found 

 now many terraces or benches rising one above another, 

 the highest marking the greatest extent of the lake. 

 About Ontario the highest is 500 feet ; about Lake Erie, 

 250 feet ; about Lake Superior, 330 feet. These lakes 

 doubtless at that time ran together, forming a vast sheet 

 of water which drained southward through the Mississippi 

 River into the Gulf. At the same time an enormous lake 

 covered the region about Lake Winnipeg and drained 

 through the Minnesota Eiver into the Mississippi. This 

 ancient lake has been called Lake Agassiz. 



River-Deposits. The section, Fig. 348, represents in 



FIG. 348. Ideal section across river-bed in drift-region. 



a general way the condition of the rivers in all the drift- 

 region. Beneath the present river-bed, r, there is a much 



