1 
78 IOWA ACADEMY OP SCIENCES. 
above the upper rapids may have trained southeastward 
through the Green river basin to the Illinois. Hirshey has 
suggested a northward discharge for the headwater portion of 
the basin,* a suggestion that awaits adequate investigation. 
The preglacial valley, which passes the lower rapids on the 
west, is nearly coincident with the present Mississippi, from 
the head of these rapids up to Muscatine, but its position 
farther north has not been ascertained, nor has the size of 
its drainage basin been even approximately determined. It is 
probable, however, that much of eastern Iowa was tributary to 
this preglacial line. 
DATE OP THE DEPLECT[ON ACROSS THE LOWER RAPIDS. 
In previous years attention has been called, both by Mr. 
Fultz and myself, to evidence that the region around the lower 
rapids presents a complicated glacial history, f It has been 
shown that one ice field extended southward from Kewatin, in 
the Dominion of Canada, across Manitoba, Minnesota and Iowa 
into Missouri and that it spread eastward beyond the valley of 
the Mississippi, from near the southern end of the driftless 
area of the upper Mississippi, to the vicinity of Hannibal, Mo. 
Two invasions may have been made by that ice field with an 
intervening deglaciation interval of some length, as indicated 
by Bain |. The later, and probably the more extensive, 
advance is referred to the Kansan stage of glaciation. 
It has also been shown that subsequent to the Kansan stage 
of glaciation an ice field extended from Labrador and the 
heights south of Hudson bay southwestward across Michigan, 
the Lake Michigan basin and Illinois into southeastern Iowa. 
The Kewatin ice field not only covered the preglacial valley 
near the lower rapids, but also the district which the stream 
traverses in passing the rapids. It was thus liable to have 
displaced the stream to a much greater extent than the deflec- 
tion past the rapids, as indicated below. The invasion from 
Labrador, on the other hand, appears to have barely reached 
to the rapids, and may not have interfered seriously with 
drainage across them, though it greatly disturbed the course 
* American Ueolog’ist, Vol. XX, 1897, pp. 346-363. 
+ F. M. Fultz, Proc. Iowa Acad, of Sciences for 1895, Vo1. II, pp. 309-313. 
»bid. 1898, Vol. HI, pp. 60-63. 
Frank Leverett, Science, .Jan. 10, 1896. 
American Gieologrist, Feb.. 1896. 
Bull., No. 3, Obi. Acad. Sci., May, 1897. 
Proc. Iowa Acad. Sci., 1897, Vol. V, pp. 71-74. 
+ Proc. Iowa Acad. Sci. for 1897, Vol. V, pp. 83-101. 
