POSTGLACIAL DEVELOPMENT OF CONNECTING RIVERS OF GREAT LAKES. 



479 



As Cole points out, the "bottom clay" fills all the lower parts of the valley between Lake 

 Huron and Detroit, and is in fact a great deposit of lake clay laid down probably in the large 

 glacial Lakes Arkona, Whittlesey, and Warren. The ice barrier is known to have stood a mile 

 north of St. Clair for Lake Whittlesey, and somewhere in the south part of Lake Huron for 

 Lakes Arkona and Warren. 



The sediments contributed to the delta are derived from three sources: Streams tributary 

 to St. Clair River bring in moderate quantities of sediment in times of flood; the river itself 

 erodes its banks and bottom, cutting away the banks rapidly in a few localities and carrying 

 the material to the delta; Lake Huron contributes sediments cut away during storms. Cole 



Figure 11. — Map of St. Clair delta. 



quotes interesting estimates made by O. B. Wheeler * of the United States Lake Survey, on the 

 amount of sediments derived from this last source. The estimates have considerable elements 

 of uncertainty but seem to show that the quantity is at least twice as great as that derived 

 from all other sources. 



CHARACTER OF THE DELTA. 



Some of the more important facts stated by Cole and by Lane in an introduction to Cole's 

 report may be summarized as follows: From its head to its front the delta measures nearly 15 

 miles on a line running south-southwest from the head of Russell Island. Transverse to this 



i Kept. Chief of Engineers U. S. Army, 1885, pt. 3, pp. 2199-2202. 



