548 J. E. TODD — PLEISTOCENE PROBLEMS IN MISSOURI. 



131,800 square miles in the United States; that is, one-half of Dakota, 

 one-third of Minnesota, and one-sixth of Iowa. Besides, there was 

 probably as great an area in Canada to be added, because the upi^er 

 Saskatchewan at that time doubtless drained into the Missouri. 



The ablation of certain Alpine glaciers as estimated by Desor is 10 

 feet a year. Forbes estimated it as over 20 feet, and as high as 2^ inches 

 per day has been observed. It seems not unreasonable to count most of 

 this area in the zone of ablation, and averaging 10 feet for the United 

 States area alone, or 5 feet, to be very liberal, for that of the United States 

 and British America. Supposing the latter to equal the former, we would 

 then have 250 cubic miles of water furnished per year, or ten times the 

 amount now discharged by the Missouri. In this we have not taken 

 account of the water derived from the rest of the basin, which, if not 

 less than now, and counting in the extension then existing into Canada 

 as equal to the part occupied by the ice, we ma^^ put down, at a moderate 

 calculation, that the river discharged eleven times as much water as at 

 present, with the probability of its discharging, at least for certain years, 

 twenty times as much. What corrasion this flood would accomplish 

 we scarcely have the means of calculating, but can conceive that it would 

 be fully adequate to the work. The ice-sheet would have discharged 

 water into the Missouri river until it receded to the fourth moraine ; 

 then its waters would mostly have reached the Mississippi through the 

 Minnesota and rapidly completed the work which that stream had pre- 

 viously well advanced. The prominent drift terraces and filled chan- 

 nels, capped with loess, may confidently be referred to the recession of 

 the ice from the principal nioraine. 



Conclusions. 



In conclusion it ma}^ be noted briefly that the most serious objections 

 to the glacial hypothesis for this region are : first, the great difference in 

 elevation between the drift of Missouri and Illinois, with the absence of 

 northern erratics in the lower Missouri and Meramec and along the Mis- 

 sissippi at higher altitudes, and last, but not least, the apparent impos- 

 sibility of the land-ice reaching central Missouri without overflowing 

 the Wisconsin driftless area. The most weighty difficulties with the 

 lacustrine and fluviatile theories are the nature of the deposits and the 

 great depth and width of the troughs of the Missouri and Mississippi. 

 Possibly more careful researcli in the nature of deposition and erosion 

 may remove them. It seems not improbable that a combination of the 

 last two may approach the truth more nearly than either one alone. 



Vermillion, S. D., December 22, 1893. 



