1S92-] O [Upham. 
of coiapoim.l Jriiiiilin .-iggregations, where two or three of these 
hills, or sometimes more, are merged together at then- bases. 
Drumlins consist, at least superficially and in most cases through- 
out their entire mass, of till or boulder-clay, being unstrati- 
tied clay, sand, gravel, and boulders, mingled indiscriminately 
together, which therefore must be attributed to deposition by 
ice without moditication l)y the assorting and stratifying action of 
currents of water. They have usually an oval form, with smoothly 
rounded top and steep slopes, especially at the sides, from which 
features Prof . C. H. Hitchcock in 1876 named them lenticular 
hills, the first distinctive term applied to these drift accumula- 
tions in this country. Subsequently the name drumlins, used by 
M. H. Close ten years earlier for similar hills and ridges of till in 
Ireland, has come also into common use here. 
Oval or elliptical forms of drumlins prevail, Avith rare excep- 
tions, in Xew Hampshire, Massachusetts, and Connecticut. In 
some other districts, as in central Xew York, these hills vary from 
the oval type to prolonged ridges, running nearly straight several 
miles; and in eastern Wisconsin, as described by Chamberlin, 
they :ire prevailhigly circular and dome-shaped on some areas, 
being therefore called mammillary hills, while in other localities 
they occur mainly as long parallel ridges. Wherever drumlins 
are found, their longer axes trend in parallelism with the courses 
of the glacial striae and transportation of boulders, that is, with 
the|current of the ice-sheet. Glacialists are agreed that this rela- 
tionship and the very regular and smooth contour of the drum- 
lins resulted from the moulding action of the overriding ice, to 
which masses thus elongated opposed the least resistance. 
In the areas of their greatest development the drumlins range 
in heiglit from 25 or 50 feet up to 200 feet or rarely more, and 
proportionally in length from an eighth of a mile to one mile, or, 
in tracts where they become long riilges, two to three miles or 
more. The slopes of their ends are gentle or moderately steep, 
having from 5 to 20 feet of ascent in a distance of a hundred feet ; 
but the steeper ascent of their sides varies usually fiom 15 to 30 
feet in the same distance. Instead of amassing the till in such 
prominent accumulations, we should expect that the ice-sheet 
would tend constantly to wear away the hilltops and leave thick 
deposits of subglacial drift only in depressions of the country and 
on low or nearly level land. 
