BASINS OF THE GEE AT LAKES OF AMEBIC A. 525 



2. Features of the Ontario Basin. 



Lake Ontario, as was shown in an earlier publication *, is a basin 

 bounded on its southern side by escarpments, often precipitous, of 

 which some of the steps are now submerged. At the foot of the 

 submerged escarpments a valley like that of an ancient river may 

 be recognized from the western part of the lake to near the eastern 

 end, but there it disappears, for reasons to be noted later. The 

 deepest part of this valley is 738 feet beneath the surface of the 

 lake. From this trough the floor of the lake rises gradually, or with 

 occasional low steps, to the northern shore. In short, the basin was 

 once an old land-valley traversed by a river. At the western end 

 of the lake borings have revealed an old channel, having a lateral 

 depth of 292 feet. This is the continuation of the canon of the 

 Dundas Valley, which is about two and a half miles wide, bounded 

 by rocky walls nearly 500 feet high, capped with Niagara Lime- 

 stone. Down this valley the waters of the ancient Erie basin once 

 flowed t. 



If the waters of Lake Ontario were withdrawn, its present basin 

 would be a broad valley, continuous with that of the St.-Lawrence 

 valley, having a breadth of thirty or forty miles. Into this plain, at 

 a point about twenty miles east of Toronto, there is a channel, ap- 

 proaching the shore, whose bed is 474 feet below the surface of the 

 lake J, but with boundaries submerged to only 200 feet. This de- 

 pression trends southward and joins that at the foot of the sub- 

 merged escarpment before mentioned §. 



3. Features of the Erie Basin. 



The floor of Lake Erie is a broad flat plain, now rarely submerged 

 CO a depth of more than 84 feet, and usually less. Only a small 

 area, situated directly south of the western end of Lake Ontario, is 

 of greater depth, and there the greatest sounding is 210 feet ||. 

 But from this region the Erie Valley was drained by the Grand 

 Kiver and Dundas Valleys into the western end of Lake Ontario, as 

 was shown in 1881 ; for the Niagara river did not then exist. 

 Numerous tributaries of the modern shallow lake flow over deeply 

 buried channels, the deepest of those discovered being 228 feet 

 below the lake-surface, as described by Dr. Newberry ^, although 

 the floor of that portion of the lake is nowhere over 84 feet below 

 the surface of the water. 



Similar channels, buried to depths below the floor of the eastern 

 end of Lake Erie, near Buffalo, have been described by Dr. Julius 

 Pohlmann**. The borings into many others in the region of the 



* " Discovery of the Preglacial Outlet of the Basin of Lake Erie into that of 

 Lake Ontario," by J. W. Spencer; Proc. Am. Phil. See, Philad. 1881. 

 t See " Diseoyery of the Preglacial Outlet of Lake Erie," &c. 

 X See British Admiralty Chart of Lake Ontario. 

 § See U. S. Lake-Survey Charts of Lake Ontario. 



11 See U. S. Lake-Survey Chart of Lake Erie. ^ Geology of Ohio. 



•5^* Paper read before the Amer. Assoc. Advanc. Science, 1883. 



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