OBJECTIONS TO SUBGLACIAL HYPOTHESIS. 543 



Another difficulty is the remote distribution of the ice. We have 

 ah'eady alluded to the great distance at which the drift is found in 

 northern Missouri from the original center of dispersion. This was at least 

 as far away as the northern boundary of Minnesota. Considering the 

 movement of the ice at later stages, it must have advanced either down 

 the vallej^s of the Red, James and Missouri rivers or over eastern Minne- 

 sota across the valle)'' of the Des Moines and the high land in southern 

 Iowa. If we suppose the glacier moved b}' the former route, this is cer- 

 tainly its greatest advance toward the south. If by the latter, we can 

 scarcely conceive how ice should have flowed in this direction rather 

 than into eastern Iowa and into the region which is known to be drift- 

 less. 



Jf these two streams were confluent, as is commonly assumed, we may 

 state the difficulty as follows : It matters' little what the original starting- 

 point of the glacier was. From the analogy of the Greenland ice-sheet, 

 in order to extend the ice to the vicinity of Glasgow, central Missouri, 

 the ice-sheet may have risen to an altitude of 8,000 or 9,000 feet at the 

 north line of Iowa. The distance of the margin of the drift in eastern 

 Nebraska from the western margin of the Wisconsin driftless area is 

 barely 300 miles. With such an altitude of ice, why should the ice have 

 extended southward into central ^lissouri full 300 miles, but scarcely 

 half that distance eastward, else it would have encroached upon the 

 Wisconsin driftless area? The great altitude of the western margin in 

 Nebraska may have prevented its flow in that direction, but the present 

 altitude of the driftless area is no greater than the high land in southern 

 Iowa. If, as is thought b}^ many, there was a northern depression during 

 this stage of the ice this difficulty would have been greater. Should it 

 be suggested that Greenland is a colder region than this was during the 

 Ice age, and that therefore the ice need not be assumed to have been as 

 thick, again the difficulty is only aggravated. 



THE LACUSTRINE THEORY. 



The Thcuru stninL — Probably the best presentation of this hypothesis 

 would be about as follows : Such was the altitude of the region under 

 consideration that all portions now known to be strewn with northern 

 erratics at a high level were simultaneously or successively brought be- 

 neath the waters of a great glacial lake or system of lakes, and that the 

 loess was probably deposited in a later and greater extension of the same 

 which probably attended the melting of the larger portion of the ice- 

 sheet in the Missouri valley. The ice-sheet may have entered the state 

 from the north to an indefinite distance, but the larger portion of the 

 area was covered with subaqueous formations. Into this lake, or series of 



