330 THE ICE AGE IN NORTH AMERICA. 



their excessive burdens, and had subsided to something like 

 their present volume, 



As illustrating the capacity of the glacial theory to ex- 

 plain the otherwise unaccountable facts connected with the 

 recent changes in the drainage of the glaciated region, atten- 

 tion is directed to two or three interesting localities east of 

 the Alleghanies, where the dry beds of abandoned streams 

 have been discovered. 



We will first consider the outlets of an interesting glacial 

 lake which temporarily occupied the upper part of Contocook 

 Valley in Hillsborough county, JS". H., the details concerning 

 which were furnished as early as 1878 by Mr. Upham, in 

 the New Hampshire Geological Keport. The Contocook 

 River now empties into the Merrimack a little above Con- 

 cord, and flows in a direction north-northeast. As a conse- 

 quence, the present outlet was, toward the close of the Gla- 

 cial period, obstructed by ice some time after it had melted 

 off from the southeastern portion of the valley. During that 

 period a lake was held in the portion of the valley freed 

 from ice, at a height sufficient to turn the drainage tempo- 

 rarily to the south and southeast. At first the drainage was 

 over the water-shed in Rindge, through Ashburnham and 

 Winchendon, Mass., and thence into the Connecticut. The 

 reality of this line of drainage is evidenced by the exten- 

 sive kames and gravel deposits extending from the Conto- 

 cook Valley through the towns of Rindge and Winchendon. 

 "When the ice had withdrawn a little farther north, an outlet 

 was open to the southeast into the Souhegan River, and 

 thence into the Merrimack. The evidence here is also con- 

 clusive that, for a period, a stream of water eighty feet deep 

 poured through this pass, and the lake formed in front of 

 the ice was in its greatest extent thirty miles long, and from 

 two hundred to two hundred and fifty feet in depth. The 

 evidence of this remains in delta terraces at that level 

 formed at various points where streams came into the lake. 



Another instance is in Grafton county, ~N. H., on the line 

 of the Northern Railroad, between Grafton Centre and East 



