382 



FIRST YEAR SCIENCE 



Lake Agassiz in honor of the great scientist who did so 

 much toward the explanation of glacial phenomena. Gla- 

 cial lake plains of this kind are found not infrequently. 

 They now form fertile areas of great agricultural value. 



172. Waterfalls Due to Glaciation. As the ice spread 

 over the country it filled the river valleys in many places 

 with debris. When the ice melted away, some rivers 

 could no longer find their old courses and were forced to 

 seek new ones. It frequently happened that in deepen- 

 ing these new channels the river came upon buried ledges, 

 and in wearing these down, rapids and falls were devel- 

 oped. In this way many 

 of the water powers of 

 New England and the 

 northern states were 

 produced. 



The Merrimac fur- 

 nishes a fine example of 

 water power due to 

 glaciation. The great 

 manufacturing cities of 

 Lowell, Lawrence and 

 Haverhill would not exist had not the river been displaced 

 from its previous channel by the glacial ice, and in devel- 

 oping its new valley come upon ledges which it is now 

 trying to reduce to grade. The Niagara is another notable 

 example of vast water power due to the displacement of 

 drainage by the ice. It is probable that in pre-glacial time 

 there was a river which carried off the drainage of the area 

 now drained by the Niagara, but it did not flow where the 

 Niagara now flows. 



173. Glacial Period. Evidences of an ancient ice cov- 

 ering are seen in North America, even as far south as the 

 Ohio River and extending over a vast region which now 



NIAGARA FALLS. 



Due to rearrangement of the drainage 

 by the ice of the Glacial Period. 



