JPISE GIL CHAE, WAULILIDIGS (UF TIGER. NUNS SUS SILELEN 749 
or but six-tenths of an inch per mile. Under present conditions 
the river will soon remove the rapids and reduce its rate of fall 
to that of the rock floor, if not, to a lower rate. 
The Missouri Valley—F¥or purposes of comparison with the 
Mississippi Valley, and valleys further east we introduce at this 
point a few statements concerning the Missouri Valley, followed 
by a table showing the elevation and slope of the valley floor 
and of the present stream, from Sioux City to the mouth of the 
stream. The table is compiled chiefly from data given in the 
annual reports of the Missouri River Commission for 1890 and 
1892. We are indebted for additional data to Mr. George S. 
Morison of Chicago, chief engineer in the construction of sev- 
eral bridges across the Missouri. We are also indebted to Pro- 
fessor J. E. Todd, State Geologist of South Dakota, for sugges- 
tions, both published and unpublished, concerning the history of 
this youthful but somewhat overgrown tributary of the Mississippi. 
The researches of Professor Todd and others have developed 
the fact that the present course of the Missouri, through the 
Dakotas is independent of preglacial valleys, and dependent 
upon the position of the ice margin. Its course along the 
boundary of Nebraska is considered by Professor Todd to ante- 
date but little the late ice invasion which was marked by the 
Altamont moraine. He finds evidence that Lake Cheyenne 
persisted, in eastern Nebraska, southeastern Dakota and south- 
western Iowa, to the beginning of the glacial period’ and infers 
a very low altitude for the region up to that time, one not cal- 
culated for deep erosion of valleys. He writes that he has not 
yet found a clear case along the Missouri Valley, of excavation 
prior to the glacial deposition. In examinations of the rock sur- 
face exposed in sinking the piers of the bridges at Blair and 
Omaha, he failed to discover evidence of glacial action. Alleged 
glacial deposits in the valley lower down, as at St. Charles, 
Missouri, he thinks capable of another interpretation. The 
entire valley may prove to be more recent than the Kansan stage 
of glaciation. 
*Evidence that Lake Cheyenne continued till the Ice Age, by J. E. Topp, Proc. 
A. A. A. S., Cleveland Meeting, Vol. XXXVIL., 1888, pp. 202, 203. 
