PHYf^ICAL AND CLIMATIC SETTING 25 



The rocks in the course of the ice were ground up 

 and carried in the direction of its movement, usually 

 south. Material from various sources was mixed. 

 Bowlders were mingled with finer material. Deep 

 deposits were laid down in hollows, perhaps none on 

 the eminences. 



After a long and indefinite time, the ice began to 

 retreat. Its margin fluctuated from season to sea- 

 son or from century to century. Where it stood for 

 any length of time a ridge of earth was left and 

 these terminal moraine-bands may be traced across 

 the State in various places. 



Great volumes of water were formed by the melt- 

 ing of the ice. This water accumulated in the hol- 

 lows and valleys and flowed off to the southward as 

 greatly flooded streams that formed broad bottoms of 

 gravel and sand and fine loam. 



As the ice margin retreated to the northward, it 

 was, in all the western part of the State, moving 

 down the general slope of the country. Conse- 

 quently, the drainage water accumulated as ponds 

 and lakes between the front of ice and the land 

 divide in the valleys. As the ice retreated further 

 north, these lakes found new outlets at lower levels. 

 They connected through the valleys and finally came 

 to have a large extent. ]\rany successive levels of 

 these are recognized in the more important valleys 

 of the Finger Lakes region and the Genesee Valley, 

 marked by the level of the benches of gravel and 

 sand along their walls. At one stage this succession 

 of lakes connected with the Lake Erie basin and 



