1872.] 113 [Perry. 
Iam amazed at Professor Dana’s denial of their presence, and am 
unable to account for it, unless on the ground that his knowledge 
comes from Geological Reports in which lateral moraines have been 
usually described under other names. Indeed, so abundant are the 
morainic heaps and ridges characteristic of the Local Glacier times, 
that I confidently look for a much more extensive recognition of their 
fragmentary remains, in different portions of New England,—under 
one or another of the forms mentioned,—as traces of glacier-action 
come to be better understood, and more careful examinations are 
made. As nicer discrimination is brcaght into play, much will be 
discovered, and found to be attested by actual facts, which was once 
ignored, and is perhaps now scarcely deemed possible!. 
As to the light which this phase of the subject is calculated to throw 
on the relative duration of the Glacial period, a few sentences should 
be added. ‘Taking the Richmond angular erratics as furnishing an 
item of evidence,— presuming that they extend as far as the longest 
boulder-trains, as.I have been credibly informed is the case; remem- 
bering that the time of their removal from their native ledges and 
deposition could have been only from the moment the peaks, from 
which they were mainly derived, were laid bare, until the remainder 
of the ice-sheet in the neighborhood was wasted: that they extend at 
least twenty miles ; that the rate of motion of the ice-mass, according 
to Professor Dana, could not have exceeded a mile in a century; and 
that the movement of the ice was no doubt much more rapid than that 
of the underlying boulders,—I find that at least 2000 years were re- 
quired for the thawing of ice from five to seven hundred feet thick, in 
a given locality. Grant that the thickness of the ice in that place, at 
that time, was 600 feet, and that of the ice-sheet in its prime about 
6000 feet, the entire mass must have been ten times as thick ; thus, 
other things being equal, there would be required for its melting, in 
that one neighborhood, some 20,000 years. Again, the wasting, on 
the whole, probably advanced slowly from south to north; on this 
ground another element of time enters into the calculation; it thus 
necessitates a longer duration for this part of the closing Glacial times 
1 Since the above was written, Professor Agassiz informs me that he has recently 
discovered, in great number, terminal, lateral and medial moraines in the White 
Mountain region; that within a space of about two miles he found sixteen termi- 
nal moraines;and that many of them are as distinct as any he ever saw in Swit- 
zerland.—See also his paper On the former Existence of Local Glaciers in the White 
Mountains. (Proceedings, Am. Ass. Ad. Science, Vol. x1X, pp. 161—167, or Amer- 
ican Naturalist, for Oct., 1870.) 
