Englacial Drift in the Mississippi Basin. — Up/uvn. 373 
valleys, because the moderate volume of this drift, somewhat 
evenly spread in falling to the ground when the ice melted, 
was inadequate to fill them. 
From such observations and consideration of our Minne- 
sota drift deposits, it becomes evident to my mind that the till 
of the lowan glacial readvance is mainly a formation supplied 
from englacial and finally superglacial drift falling on all the 
area of that glaciation when the ice in which it had been held 
disappeared. More than twenty-five years ago, Prof. X. H. 
Winchell clearly stated his belief in the englacial transportation 
of the drift and its exposure on the surface of the waning 
ice-sheet.* His very picturesque description of these condi- 
tions, as applied to the Glacial period, has since been, in a 
sense, verified by the discovery of the waning Malaspina ice- 
sheet of Alaska, covered on its border with drift and a grow- 
ing forest to the width of a few miles and above hundreds of 
feet of ice. Somewhat earlier, Prof. James D. Dana had pub- 
lished similar views of the manner in which the ice-sheet 
worked. During my early studies of the glacial and modified 
drift in New Hampshire, southern New England, and Long 
Island, and afterward in Minnesota, where during twenty years 
I have studied its drift deposits, all my observations and con- 
clusions fall into agreement with these views of Dana and 
Winchell. Therefore it is with a full measure of confidence 
that the same belief in englacial and later superglacial origin 
of the lowan till is here extended to its development on its 
type area of eastern Iowa, although this explanation is unlike 
the opinions of Chamberlin,t who first defined and named this 
glacial stage and its deposits, and equally discordant witlj the 
inferences of Calvin in his recent very able paper on this 
subject. J 
As Crosby has well remarked, the englacial drift probablx 
became in most regions partly banked beneath the ]:)orders 
of the ice-sheet during its departure, forming then a ground- 
moraine, while another and larger part remained in and on the 
ice and fell at last as the upper and looser part of the till.§ In 
*Popular Science Monthly, vol. iii, pp. 293, 294, July, 1873. 
fChapter xlii, in Prof. James Geikie's Great Ice Age, third edition, 
1894. 
^Bulletin, G. S. A., vol. x, pp. 107-120, March 7, 1899. 
§.A.m. Geologist, vol. xvii, pp. 203-234, A])ril, 1896. 
