Wright.] 



56 [December 20, 



In partially accepting their views, I feel that I must modify, though 

 not wholly abandon, my former opinion. 



So far we have examined phenomena; let us now come down 

 from the other direction and see if we can find a cause that would 

 reasonably produce the complicated series of facts we have pre- 

 sented. 



At the height of the glacial epoch this region was covered with 

 an ice sheet, say 5,000 feet thick. As this had slowly formed and 

 moved southward, much earthy material had been incorporated into 

 the frozen mass. Some had worked from below upward through 

 the crevices, as the mass moved onward; far more had fallen upon 

 it, after the manner familiar in ordinary lateral moraines, or been 

 scraped off, and worked into it at various levels, from the sides of 

 the mountains which it had passed and enveloped. The detritus 

 would be peculiarly abundant in the glacier in the line of motion 

 from the sides of mountains, like the Franconia Range, or the White 

 Mountains, and would be found in the ice in a diagonal belt passing 

 upwards from the base in a line parallel with the sloping side of the 

 mountain, and would exist in the glacier in definite lines, correspond- 

 ing to the direction of the general movement from the mountains 

 southward. 



When the climate began to ameliorate, so that the glacial sheet 

 commenced to diminish, this diminution would take place in at least 

 two directions ; the southern boundary would retreat northward, and 

 the thickness would diminish from the top. For example, there 

 would be a time when the thickness had shrunk from 5,000 feet to 

 2,000 feet. If this had been mostly due to melting from the top, all 

 the earthy material of the upper 3,000 feet would have accumulated 

 on the top of the remaining portion of the glacier, after the manner 

 of the dirt on a melting snow drift. In the lines of motion from the 

 higher mountain prominences, there would of course be an excessive 

 accumulation, forming a medial moraine. Now the material of this 

 moraine would not settle down regularly and silently. But after 

 a certain stage in the accumulation of debris, the ice would be pro- 

 tected under it so that it would have an additional elevation above 

 the general melting mass, and as the melting progressed, the detritus 

 would slide off the slopes on one side or the other. By the time 

 fragments of rock had rubbed together in a lineal motion of many 

 miles, and in a perpendicular descent of five thousand feet, they 

 would be well worn. Pockets, and channels would be formed in the 



