46 CONTRIBUTIONS TO THE 



The foregoing description of the Devil's Pulpit, although ex- 

 tended, is inadequate when viewed from the stand-point of its 

 importance as a factor in the measurement of geological time or 

 the value of its testimony to the stupendous work performed by 

 water in a distant age ; and the preparation of this paper was un- 

 dertaken partly with the hope that the attention of geological 

 experts might be enlisted in explaining its further relations to 

 the general subject of ^'lacial phenomena. 



We now find established, by evidence as ample as it is con- 

 vincing, four prime facts : i. A remarkable example of water 

 erosion upon a grand scale. 2. The dry bed of a once powerful 

 and long-continued stream. 3. That the stream was fed mainly 

 by water from melting ice-fields. 4. That there is no evidence 

 of the existence of any stream capable of performing the work 

 within the historic period. 



It must further be concluded that a stream of great volume 

 flowed at the same time through the great north and south val- 

 ley to which allusion has been made, and that extensive sections 

 of this valley were occupied by one or more great lakes. It on- 

 ly remains to corroborate the conclusions reached by citations 

 from admitted authorities. The following extract from Wright's 

 " Ice Age in North America " will well support the views ad- 

 vanced, and at the same time afford an impressive example of 

 the part played by glacial dams. Prof. Wright's account is 

 based upon detailed surveys by Mr. Upham, the results of which 

 are published in the New Hampshire Geological Reports: 



" The Contoocook river now empties into the Merrimack a lit- 

 tle above Concord and flows in a direction north-northeast. The 

 present outlet was, towards the close of the glacial period, ob- 

 structed by ice some time after it had melted off from the south- 

 eastern portion of the valley. During that period a lake was 

 held in the portion of the valley-freed from ice, at a height suffi- 

 cient to turn the drainage temporarily to the south and south- 

 east. At first the drainage was over the water-shed in Rindge, 



