1895.) Minor Time Divisions of the Ice Age. 237 
for the most northern of these observed interglacial deposits. 
It therefore seems to me more likely that during this glacial 
retreat the present basin of the Red river of the North, which 
was later occupied by lake Agassiz, had a considerably greater 
altitude than now, retaining a part, probably a large part, of 
its preglacial elevation, and that it was thus a land surface 
with southward descent and free drainage along the Minnesota 
river valley to the Mississippi. The recession of the ice-sheet, 
before its renewed growth, may then have reached only to the 
southern part of the Red river valley, instead of the great far- 
ther distance to Hudson bay, which I formerly supposed in 
writing of these interglacial beds in Minnesota.’ 
The erosion of numerous and large interglacial stream 
courses in the early drift sheet of southern Minnesota and 
northern Iowa, including the Minnesota river valley and its 
continuation past Brown’s Valley and above the bed of lake 
‘Traverse, channeled then apparently about 50 feet (or more) 
below the general surface of the adjoining country to the level 
of the Herman beach of lake Agassiz,‘ finds full explanation in 
this retreat of the ice-sheet to the vicinity of Mitchell and, 
Barnesville, 200 to 250 miles inward from its farthest limits in 
North Dakota and on the northern boundaries of the Wiscon- 
sin driftless area, but 500 miles north from its limits in Kansas 
and Missouri. 
During the ensuing stage of its renewed accumulation and 
growth, the ice-sheet reached from Barnesville about 200 miles 
westward into North Dakota, an equal distance eastward into 
northwestern Wisconsin and southeastern Minnesota, and some 
350 miles or more south-southeastward in Iowa. Not only 
were the interglacial forest beds thus covered, but a marginal 
moraine, which had been formed probably during a slight pause 
or readvance interrupting the later part of the intermediate 
- glacial retreat, was likewise buried and is now indicated by 
exceptionally abundant boulders in a stratum of the drift 
3 Geology of Minn., Final Report, vol. i, 1884, pp. 402, 406, 466, 479-485, 507, 
511, 552, 580, 581, 585-6, 609, 625; vol. ii, 1888, pp. 138, 186, 187, 199, 456, 529, 
555, 662, 668 
*Proc. A. À A. S., vol. xxxii, for 1883, pp. 222-227. Geology of Minn., vol. 
i, pp. 479-485, 507, 580; vol. ii, 134, 172, 216, 519-525. 
