200 J. D. Dana on the Glacial and 
New Haven, weighing nearly a hundred pounds. These are 
mentioned as examples of what occurred everywhere. The 
whole surface of the country, from the slopes of the higher 
mountains to the low plains, contributed to its load, the glacier 
making much loose material by abrasion where it found none 
at hand. Moreover, part of this material was gathered up 
within a few miles of where it was deposited. 
Having a thickness of 5,000 to 6,500 feet in northern New 
England and an average of 2,700 in southern, the pressure on 
the surface beneath was immense; 6,000 feet corresponding to 
at least 300,000 pounds to the square foot. Under this great 
pressure there was not only abrasion of the rocks beneath by 
the ice armed with stones in its lower surface, and also a crush- 
year only a part of its snows, so that an annual addition was 
made to the accumulation in progress. A fourth, or a third, or 
more of the snows that fell each year may have melted to de- 
seend through the crevasses, and if so the streams would have 
been sufficiently well fed, independently of the contributions 
of springs, to have kept up their flow under the mantle of 1¢@, 
* In experiments by Christie, and also by Tyndall, ice has been moulded into 
various shapes by pressure; and Tresca has produced, by forcing it 
holes, long cylinders, the ice in the operation not losing, he states, its glassy te 
ture or aspect. T: found the pressure requisite that of a column of water 
4,000 feet high. But having unlimited time at command, as with the old glacieh 
the work could be done with less pressure. 
