Bouv<§.] 
226 
[April 17, 
rocks borne by the waters found a lodging in some depression and 
there by rotation worked out the pot holes. The ice might move 
on and the waters descend through the moulin far from where they 
first fell, yet continue their flow in the same direction as at first 
and go on with the work of rotating the contents of the hole through 
a whole season. In such case there could be, of course, no reason 
to expect elongation. 
The fact that pot holes have been found in near proximity and 
in such positions relative to each other, showing them apparently 
to be the result of independent falls of water, as in the case of 
the “Well” so-called, of the holes described at the distance men- 
tioned from the others, leads to a consideration of what has been 
noticed in the Alps. Observation upon the glaciers there shows 
that as a crevasse is carried forward by the general movement of 
ithe ice from where it received the flow of waters in the summer, and 
winter cuts off the supply, it closes, leaving only upon the surface 
of the glacier a mark showing where it had once been. Subse- 
quently, a new one is formed just where in relation to the land at 
the margin of the glacier, the former one existed ; and the waters 
of the succeeding summer again descend upon the rock surface 
Bear where they before fell, but not often, probably, in exactly the 
•same place ; and thus other pot holes are formed contiguous to 
those of a preceding season, and yet far enough distant to make it 
•evident that they were not produced by the same flow of water. 
Respecting the formation of the crevasses in about the same 
(places on the ice sheet, there can be no question but that this is 
•due to the irregularities of the subglacial surface ; and as high 
ridges transverse to the direction of the glacial flow must favor 
their formation, it is no wonder that pot holes are often found in 
the slopes of such ridges and at their bases, as in the case of those 
described at Cohasset. 
In the discussion of this paper, Mr. Warren Upham stated that he 
had examined the locality in company with Mr. Bouve and Profes- 
sor Crosby, and that the contour of the vicinity convinced them of 
the impossibility that any stream could have flowed there, excepting 
when the country was partly or wholly enveloped by the ice-sheet. 
But the glacial origin of these and other “Giant’s Kettles,” by water- 
falls plunging through moulins of the ice-sheet, seems difficult to be 
understood, because the observations of Agassiz and others show 
