732 ALLEN DAVID HOLE 
valleys is about 1,200 feet. This is not, however, a measure of the 
thickness of the glacial deposits, but is an indication of about the 
maximum thickness reached by the glacier at the point in question. 
The morainal deposits cannot exceed from 200 to 300 feet in 
thickness, and may be considerably less. The greater part of the 
total elevation of the top of the morainal hills above the bottom of 
the valley is due to the underlying rock in place which constitutes 
the walls of the canyon-like valley down which the glacier moved.’ 
2. In the earlier epoch or epochs —The occurrence of the older 
drift at and beyond the edge of the more recent drift is conclusive 
proof that the earlier glaciers covered a greater area than the more 
recent ones. With the exception of a few square miles in the 
northwestern part and possibly also in the southwestern part the 
entire area of the quadrangle must have been affected by glaciers 
in the earlier epoch. The appearance of the surface for a con- 
siderable length of time in that epoch must, therefore, have been 
that of snow and ice, except as it was broken here and there by 
projecting tops of peaks and ridges on whose steep slopes the snows 
could find no resting-place. In view of the great extent of the 
glaciers of the earlier epoch, and the large size of the bowlders 
which constitute a part of their deposits, glacial action in that 
period must have been sufficiently vigorous and long continued to 
produce important modifications in the topography. The details 
of such changes, however, can never be known; we can only be sure 
that the glaciers of that period played no small part in the general > 
process of degradation which is still going on in the region. The 
isolated patches of earlier drift which are seen today are believed to 
be remnants of the moraines of that early period; those moraines 
must have retarded the erosion of the formations on which they 
were deposited, and so the elevation of the mesas and ridges on 
which these patches of drift occur must be somewhat greater than 
it would have been except for the protection thus afforded. With- 
out doubt, therefore, some of the hills and ridges in the quadrangle 
owe part of their present elevation and some details of their con- 
figuration to the work of glaciers in the earlier epoch; but there are 
no means at hand by which to determine even approximately the — 
amount of modification due to this cause. 
