The Madison Type of Drumlins. — Uphain, 81 
englacial and superglacial drift contained in the ice and ex- 
posed on the surface when its boundary was withdrawn across 
this area. On the lowlands adjoining the hills this sheet ap- 
pears to have been from three to eight feet thick. Neither 
there nor on the hills do I see need of supposing, with Prof. 
R. D. Salisbury,* that some part of the fine silt of this till had 
been blown upon the ice-sheet from the driftless area, unless 
it may be so small an addition as the "cryoconite" observed 
by Nordenskiold and Nansen on the western half of the Green- 
land ice-sheet.f 
My observations, like those of Profs. Chamberlin and King, 
find the till upon the Madison drumlins more plentifully 
charged with boulders and smaller stones than the correlative 
deposit on the lowlands. The transportation of these rock 
fragments from the adjoining portions of the ice-sheet to the 
drumlin hills I think attributable to convergent glacial cur- 
rents flowing downward from contiguous higher tracts of the 
ice to the depressions of its surface beneath which the sand 
and gravel had been amassed.^ In reference to the theory of 
the origin of drumlins which I present in the paper here cited, 
I may reply to the principal objection urged against it by 
Prof. W. M. I)avis,$ Mr. George H. Barton, || and Prof. T. C. 
Chamberlia,** namely, the local derivation of much of the 
drift forming the drumlins, that I have partly considered this 
objection in the original paper, as it seems to me sufficiently 
for such drift as is derived from distances of one mile or more. 
The upward moving basal currents of the ice probably carried 
the drift up from the land to bights equal to that of thelargesl 
drumlins within one or two miles of advance, as is shown by 
the Pinnacle hills esker. Rochester, N. Y. Moreover, wherever 
drumlin accumulation took place on a land surface, with no 
ice beneath, as may have been the more common way, much 
*Am. Geologist, vol. xn, i». 172, Sept., 1893. 
fA\i. Geologist, vol. viit, p. 147, Sept., 1891. 
^"Conditions of Accumulation of Drumlins," Am. Geologist, vol. \. 
pp. 139 If.-.'. Dec, 1892. 
§Proi dings, Boston Soc. Nat. Hist., vol. \.wi. pp. i; •„>:;. Nov. 10, 
1892. 
Jlbid., pp. 23^25. 
**Journal of Geology, vol. i, pp. 259 '.'til. April-May, 1893; also see pp. 
521-524, July-Aug., 1893. 
