GLACIATION IN THE TELLURIDE QUADRANGLE 731 
however, that this method of statement does not present complete 
information as to the number of glaciers which existed, for on each 
side of the quadrangle glaciers moved to undetermined termini 
beyond its borders; and on two sides glaciers moved into the 
quadrangle from points of origin outside. Within the quadrangle, 
however, there are between 80 and go points of origin, the exact 
number reckoned depending upon how many of the smaller tribu- 
taries of a given valley are considered as independent areas of 
initial movement. Of termini there are 14. 
The total area glaciated in the more recent epoch is estimated at 
near 150 square miles. The greatest length of glacier lying wholly 
within the quadrangle, measured from terminus to most remote 
point of origin, is 153 miles. Some of the glacial ice within this 
quadrangle, however, was tributary to the great Animas Glacier 
which is reported by Mr. George H. Stone’ to have been 60 miles or 
more in length. 
The maximum thickness of ice was probably something in 
excess of 1,500 feet. The slope of the surface of the ice varied from 
probably 1,000 feet per mile in the upper part of small valleys to 
200 feet per mile or less in the lower part of the course of the larger 
glaciers. 
The amount of glacial erosion cannot be estimated accurately 
from the deposits which are found, owing to the fact that much of 
the débris must have been carried away by the swift streams. But 
even when allowance is made for the disappearance of a considerable 
amount, it would seem that the whole amount removed by the ice 
was not in excess of 100 to 200 feet in average thickness for the 
glaciated tract; the maximum amount of erosion may, in places, 
have reached 400 to 500 feet. 
As already stated in the description of the drift in the valley of 
the San Miguel River, the deposits near Keystone may be as much 
as 400 feet in thickness; this depth of drift is, however, very 
unusual for this quadrangle. Outside of the Keystone deposits 
the thickest are probably those found on the mesa between Bilk 
Creek and Lake Fork. The maximum height here of the top of 
the morainal hills or ridges above the bottom of the adjacent 
t Jour. Geol., I, 471 ff. 
