{')•! The American Geologist. September, 1893 
details, is such that this amount seems scarcely allowable. 
Even half this amount appears excessive. On this basis, as- 
suming a rate of erosion one quarter as great as thai of the 
.M nit- glacier, t hat is. less than a quarter of an Inch a year, the 
duration of the last glacial epoch would still he within his 
estimate. While the objecl of this article is not to make an 
estimate of the age of the glacial period in years, bul rather 
to show that its age is not great, this general conclusion is 
stated to show the agreement without insisting upon its value 
even as an approximate estimate. 
Since in the early youth of glacial action the ice is chiefly 
engaged in the removal of such disintegrated material as may 
have vered the country at the time of the appearance of the 
ice-sheet, it would he expected that at the margin of this 
sheet, if anywhere, the relies of this stage would be found to 
exist. If this stage has been passed through, and it seems 
certain that it must have been, somewhere near the margin of 
the drift we ought to expect to find material thus derived. 
If, perchance, the glacier was at first more extensive than it 
was in later stages, it would not be unnatural to expect to find 
these deposits outside of the limits of the more northern 
moraine which marked the most long continued stand of the ice. 
Disintegrated deposits do exist south of the terminal 
moraine of the last glacial epoch and these are ascribed 
by many to a much earlier and distinct epoch, although by 
some this conclusion is controverted. The author has no per- 
sonal knowledge of these deposits and does not therefore feel 
competent to pass judgement upon them, although arguments 
which seem unanswerable, particularly when taken in connec- 
tion with outside evidence of diversity of the glacial period. 
have caused him to accept the evidence which has been pre- 
sented in proof of two glacial epochs. Nevertheless, in view 
of the fact that there are ;i number of glacialists who find 
evidence of the opposite character, this possible explanation 
of the disintegrated nature of the extra-morainic drift should 
be considered as a working hypothesis. Thereappears to be no 
escape from the conclusion that disintegrated drift was carried 
to the ice margin, unless it is assumed that the interglacial 
epoch was exceedingly brief ; and if such drift has been carried 
there, one may well ask the question, where is it at present ? 
