PI eixf (><■(' lie PajHi-s, (/ttaira Meetuig <>f (r. S. ^[. 17'.' 
sheet, and were deposited, like the gravel and sand eskers of 
other regions, in ice-walled channels of glacial rivers during the 
departure of the ice. 
In the ensuing discussion, Prof. Salisbury spoke of the ex- 
emption of the residuary clay and later of the forest bed from 
erosion by the ice invasions as phenomena of the marginal por- 
tions of the areas covered b}' the ice-sheets, while their inner and 
central portions were deeply eroded. 
Prof. C. 11. Van Hisk referred to the large size of the boulders 
in the later drift, which would suggest their probaltle derivation 
from a previously unglaciated region. 
Mr. Upham remarked that the preservation of the preglacial 
soil and of the forest bed shows that the ice in both its incursions 
rolled onto this district, with little or no sliding and eroding 
action of its basal portion, bringing its drift enclosed within the 
ice instead of pushing or dragging the drift beneath it which 
would have been attended with much erosion of the l)ed rocks at 
the first and of the forest bed at the later incursion. 
In the northwest part of Iowa, on the west side of this ice lobe, 
the Altamont or outermost moraine divides an area of till at the 
east from an area of loess 20 to 50 or even 100 feet higher at the 
west, showing the same relationship of the loess deposition to 
the contemporaneousl}' ice-covered country as is found by Mr. 
Mcdee in northeastern Iowa. Not onlj^ the paha, or loess ridges, 
and eskers, but also drumlins, in their parallelism of trends with 
the ice movement, afford as reliable evidence of the direction of 
that motion as glacial stria^. 
Dr. Be[>l stated that the hornblendic rocks of the Iowa lower 
till are abundantly developed northeast of lake Superior, while 
granites and gneiss predominate farther west. 
Mr. Mc(iEK, in closing the discussion of this paper, said that 
both the older and the newer drift of this district were probably 
transported in the same manner, whether subglacially or englaci- 
ally. The consideration mentioned by Prof. A'an Ilise may be 
indicative of a very long interglacial epoch l^etween the two ice 
invasions, sufficient for deep stream erosion, the isolation of 
cliff's and pinnacles of rock by weathering, and the production of 
boulders l)y disintegration of the bed rocks on the area of the 
earlier glaciation. 
I To BK CONTINIKI).] 
