GLACIAL DAMS, LAKES, AND WATERFALLS. 363 



from waterfalls, and that depth and extent of the eroded 

 valleys, which would naturally result from the prolonged 

 continuance of water-action. On the contrary, the glaciated 

 portion of the State presents a surface in the main remark- 

 ably free from the effects of prolonged water-erosion. The 

 northern and western portions of the State belong practically 

 to the great prairie region of the interior. 



None know just where the old outlet to Lake Winnepe- 

 saukee in New Hampshire is ; but, from the nature of the 

 situation and the analogies of the case, there can be no 

 doubt that it, together with the most of the larger lakes of 

 New England, is held in place by deposits of glacial material 

 filling up an old outlet. Doubtless, with comparatively little 

 labor, trenches might be dug which should, when not below 

 the ocean, drain them all to the bottom. There can be no 

 doubt, also, that Lake Champlain and Lake George are held 

 in their elevated positions by similar glacial dams, and such 

 is certainly the case with many of the numerous lakes which 

 dot the glaciated region of northern New Jersey. To a 

 similar origin is due the remarkable series of parallel lakes 

 in central New York, having at the present time a common 

 outlet in the Oswego River. Chautauqua Lake, now flowing 

 over a rocky bed past Jamestown into the Alleghany, is one 

 of the most elevated of this class of glacial lakes, being held 

 in place by a vast glacial deposit filling up the mouth of an 

 old outlet into Lake Erie. 



The evidence that Lake Erie is caused by the damming 

 up of the old outlet of the valley by glacial debris, has 

 already been presented, and the importance of this fact will 

 appear when we come to discuss the date of the Glacial 

 period. 



But, interesting as are these more permanent dams of the 

 Glacial period, they must yield supremacy to the temporary 

 lakes formed by the ice-barrier itself in its various adjust- 

 ments to the topography of the country. Travelers in the 

 Grindelwald Alps have their attention frequently directed 

 to the diminutive specimens of such lakes still existing 



