W. M. Dawis— Origin of Drumlins. 415 
‘post-glacial erosion ;* the faint channeling of their smooth 
‘slopes by rain measures the small amount of denudation that 
‘they have suffered since they were made. It must therefore 
be concluded that they were finished closely as we now see 
them when the ice melted away, and hence that they were of 
sub-glacial construction. 
water will at one point carry along silt and sand that must be 
dropped a little farther on where the current slackens; and the 
bank thus begun grows slowly ina form of least resistance, 
attaining a maximum size when its increase of volume has so 
far diminished the cross-section of the stream and consequently 
pared to that of a broad river. The comparison may be ex- 
region gives a smaller example of these two parts played by 
the ice. Jf the 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 0 
ice is allowed to pass, and some of the points of retardation 
* This assumes a point on which there is now a tolerably general agreement: 
namely, that kames were formed close by the front of the melting and retreating 
ice. 
_+ The recent history of this comparison is given in my paper on Glacial Ero- 
Sion, Proc. Bost. Soc. Nat Hist., 1882, xxii, 33. 
