zo 40 



206 G. F. WRIGHT — ^AGE OF DON RIVER GI/ACIAL DEPOSITS 



as when laid down. But the water from some unknown cause rose as the 

 accumulation progressed until it was 160 feet higher than now, when the 

 upper sediments of coarser gravel were deposited; then the water began 

 to fall and a period of erosion succeeded. 



This proceeded until at Scarboro a V-shaped channel, one mile wide at 

 the top and 150 feet deep, was worn in the sedimentary deposits, where- 

 upon the ice advanced again and covered the whole with sheets of boulder- 

 clay and assorted rubble drift to a total depth of 200 feet. Here certainly 

 seems to be an interglacial deposit of unusual extent. 



Nor is the character of the fossil plants and animals included in the 

 interglacial deposits any less noteworthy. Both the fauna and the flora 

 of the lower, or Don, beds indicate a much warmer climate than those of 

 iro^ucs Beach ^hc upper, or Scar- 



''^'"^ ' ^^^f boro, beds. In the 



Don beds there are 

 found leaves and wood 

 of maple, elm, ash, 

 hickory, basswood, and 

 even of pawpaw , and 

 osage orange, which 

 now flourish only in 

 latitudes several de- 

 grees south of To- 

 ronto; also, of the 

 mollusks found in the 

 Don beds, four of the 

 species are not now found in the Saint Lawrence basin, but only after 

 passing the watershed which separates it from that of the Mississippi. 



On the other hand, the upper, or Scarboro, sands and clays are wanting 

 in the species indicating a warmer climate, but abound in both a flora 

 and a fauna suggestive of Labrador and of the region north of Lake 

 Superior.^ 



In the opinion of Professor Coleman, these facts can not be accounted 

 for except on the supposition that the earlier ic.e-sheet retired from prac- 

 tically the whole region to the northward before the latter one began its 

 advance, which certainly looks very reasonable at first sight. But there 

 are a number of considerations, too much overlooked, which seem to 

 compel, or at least to permit, a contrary conclusion. 



Figure 1. — Section of Don Valley Brickyard, Toronto (Coleman) 



2 Coleman : "Glacial and interglacial beds near Toronto," .Journal of Geology, vol. 9, 

 pp. 285-310. "Lake Iroquois and its predecessors at Toronto," Bull. Geol. Soc, Am., vol. 

 10, 165-176. "On the Pleistocene near Toronto," British Assoc, for Adv. of Sci., Report 

 1900, pp. 328-334 ; Guide Book, No. 6, for International Geological Congress, pp. 10-34. 



