Ac<->inniJ(it/on of Di'iirnlin-s. — Iphdni. 353 
uneiiual distribution of the rubbish beneath it. If tlie faster motion 
at one place causes an excess of erosion there, the skjwer motion at 
another place may bring about an excess of deposition. This differ- 
ence of action is known to prevail between the central and marginal 
j)arts of glaciated areas ; and the local accumulation of drumlins in 
an intermediate region gives a smaller example of these two parts 
played by the ice. If tlie causes of the irregular motion of the ice 
lie in the general form of the country, the location of faster and 
slower currents will be relatively permanent ; the districts of faster 
currents would be found where the greatest volume of ice is allowed 
to pass, and some of the points of retardation may be the seats of 
long continued drninlin growth.- 
For accordance with this theory, the areas bearing drumlins 
shoxild be determined cliiefl}' by the topography and rock forma- 
tions, which, however, seem to have exerted little intlnenee. The 
rapid accumulation of the drumlins appears also inconsistent 
with the belief that they were mostly supplied from drift immedi- 
ately before eroded from the land surface and transported by sub- 
glacial dragging to its place in these drift hills. 
The origin of the drumlins may be better understood, or at 
least to the writer it seems more intelligible, if we incpiire how- 
the drift which had been englacial until the time of departure of 
the ice would be deposited. 
Traiispiirtatioit of Drift info fin loin r juirf of fix; L-c-shnf. — 
It is evident that the ice-sheet in its passage over :i mountainous 
or hilh' country must gather much drift into its lower part, to as 
great hight as the altitude of the mountains and hills, by grind- 
ing off and plucking away detritus and l)locksof rock from these 
elevations, thence carrying them forward enclosed within the ice 
many hundreds of feet, and in the lee of the AVhite, Green, and 
Adirondack mountains even thousands of feet, above the ground. 
But it has seemed to some geologists difficult to account for the 
transportation of nuich drift into the ice from moderately undu- 
lating or i)lain districts, such as make the greater part of the 
drift-bearing areas of our continent and of Europe. On these 
nearh' Hat lands, however, T find at localities in Minnesota and 
Manitoba good proofs, as they seem to me, that the thickness of 
the englacial drift was .sometimes as nuicli as forty feet near the 
ice-bonh/r wliere it was anuissing prominent terminal moraines, 
and on lines or belts where confluent ice-currents met from broad 
Am. Jour. Sci.. HI, vol. .wviii, p. 4Io. 
