334 The American Geologist. November, ib9s 
rallies; while one of the ridges seemed to us like a much-prolonged 
drumlin such as those that characterize central New York. The direc- 
tion of the ridges of till is northeast and southwest, corresponding 
both to the direction of the scratches upon the rocks and of the strike 
of the strata of Potsdam sandstone forming Rand hill, which rises to a 
considerable hight to the west. The facts as we saw them were of 
special interest from their bearing upon the discussion of Prof. 
Spencer's paper at the American Association meeting in Boston in 
which he maintained that it was necessary to suppose a subsidence of 
fifteen hundred or two thousand feet to account for the horizontal 
terraces found at the various elevations upon the flanks of both the 
Green and the Adirondack mountains. But these lateral moraines in 
Altona indicate the true explanation. 
It seems evident that in the decline of the glacial period the abla- 
tion of the ice from the surface in this region led at a certain period 
to the appearance of the tops of these mountains as lines of nunataks, 
while the Champlain valley was still full of ice. As the ablation pro- 
ceeded, the efifect of these lines of nunataks on either side was to keep 
the margins of the ice lower than the middle. This would naturally 
result from their influence in absorbing and reflecting the heat. From 
this resulted a gradual working of the glacial debris toward the mar- 
gin, where it was variously modified by the streams of water which 
were running between the sides of the ice and the mountains, much as 
is illustrated in one of Prof. Russell's photographs from the Malaspina 
glacier. In this way these high-level horizontal terraces in Vermont, 
described by Prof. Spencer, would be formed without the extensive 
subsidence which he supposes. And Mr. Baldwin is doubtless correct 
in believing that Baron De Geer has, on account of the same mistake, 
placed the extent of the subsidence at St. Albans, Vt, at two hun- 
dred feet more than it really was. Mr. Baldwin's account, on page 176 
of the paper already referred to, of the typical moraine terrace 560 
feet above the sea at Crown Point, appears to be a striking confirma- 
tion of this interpretation of the facts. 
It may be well to note, in this connection, that the discovery by 
professors Hitchcock and Richardson of Canadian boulders near the 
summits of the Green mountains, and far up upon the flanks of the 
Adirondacks, would seem to settle the question which has been in dis- 
pute between some of the Canadian geologists and those upon this 
side of the line respecting the actual invasion of the Champlain valley 
by Canadian ice. 
G. Frederick Wright. 
Oberlin, Sept. 2j, i8g8. 
