Post-Glacial Submergence. 445 
sea level and flooded with water, the theory must necessarily 
be abandoned. We can scarcely assume that such depression 
and submergence did not take place until some time after the 
disappearance of the glacial sheet, thus affording an oppor- 
tunity for the valley to be formed in the manner above sug- 
gested, for all the known evidences lead to the opposite 
conclusion. Neither can it be held that the large stream 
necessary for the work was the result of a much heavier rain- 
fall, in the period following the subsidence of the waters, than 
at present. Such a course would have resulted also in a corre- 
sponding enlargement of the upper Grand river, whose drain- 
age area is much greater than that tributary to the portion of 
the wide central valley east of its junction with the Grand. 
The narrow and tortuous upper Grand valley indicates no such 
enlargement. On the contrary, it especially disprovesit. The 
conditions which produced the large central stream appear to 
have affected none of its tributaries. 
It will be readily seen, therefore, that the submergence 
theory, in order to fulfill all requirements, must provide an 
adequate source of supply for so powerful a stream as above 
indicated ; and such source of supply must of necessity be 
placed either upon or to the east of the Grand-Saginaw water- 
shed. The task is more than I have been able to accomplish. 
Ionia, Mich. 
