1S92.] I [Upham. 
2. OBJECTIONS TO FORMER THEORIES OF THE ORIGIN OF DRUMLINS. 
Several theories of the way in which the ice-sheet produced the 
drnmlins have been suggested. The earliest was by Shaler in 1870, 
who supposed these hills in the vicinity of Boston to be remnants 
spared by the fluviatile and tidal erosion of a once continuous 
sheet of drift, which had been contained in a glacier that descended 
the Charles River valley. His later view is similar, but attributes 
the very thick drift sheet of his hypothesis to deposition during 
the earher of two epochs of glaeiation, and its erosion partly to 
sea and river action during an interglacial epoch, but mainly, for 
the peculiar sculpture of the drnmlins, to excavation and removal 
of the drift from all the intervening areas by the later glaeiation. 
To accord with this view, however, the terminal moraines of the 
later ice-sheet must vastly exceed their very moderate observed 
volume. Another objection, pointed out by Salisbury^, is that 
the drnmlins appear to be composed wholly of the newer drift. 
Hitchcock and Wright have thought the drnmlins to be perhaps 
the material of terminal moraines swept over and massed in these 
peculiar forms by subsequent farther advances of the ice-sheet. 
K this view were true, the till of the drnmlins could not have its 
nearly uniform character, but woiild contain here and there re- 
markable aggregations of boulders, and frequent irregular en- 
closures of sand and gravel would be found, representing the kame 
deposits and lenticular beds of modified drift which so conimoidy 
make up considerable parts of the terminal moraines. Salisbury 
remarks that neither the distribution nor the composition of the 
drnmlins seems to favor this hypothesis, and he therefore believes 
that they were built up beneath the ice, not being fashioned from 
hills overridden by it. 
Mr. Clarence King and Prof. J. D. Dana have conjectured that 
the drumlins, at least in some cases, were made by superglacial 
streams, charged with drift, pouring through crevasses or a moulin 
to the land surface, there depositing their drift, which afterward 
by the onflow of the ice would be subjected to its pressure and 
sculpturing. This explanation lies under similar objections to 
those of the last. 
Kinahan and Close in Ireland, Prof. James Geikie in Scotland, 
' Geol. surv. of N. J. Aun. rept. for 1891, p. 71-75. 
