526 DR. J. W. SPENCER ON THE ORIGIN OF THE 



western end of the lake have been recorded by Prof. T. Sterry Hunt *, 

 and prove the existence of similar buried channels. 



The original recognition f of the valley-like character of the 

 basins of Ontario and Erie was based upon the above-mentioned 

 characters, and upon others now supplemented by a more perfect 

 collection of facts ; but the greatest difficulty was in the occurrence 

 of the rock-bound outlet of Lake Ontario, a difficulty which obser- 

 vations have at last dispelled, as will be seen later on. 



4. Features of the Huron Basin. 



The southern half of Lake Huron is a plain traversed by valleys 

 and submerged to form only a shallow lake. Northward of this 

 shallow basin, and extending obliquely across the lake for ninety 

 miles, there is a submerged escarpment rising to a height of from 

 300 to 450 feet, facing north-eastward. The deeper part of the 

 lake then trends northward in the direction of Georgian Bay. At 

 one point the extreme depth of the submerged valley reaches 750 

 feet. The absolute depth of the rock in the deepest channel between 

 Lake Huron proper and Georgian Bay is not known, but soundings 

 show «^06 feet ; and as there is a deep channel upon the western side 

 of Georgian Bay it becomes highly probable that a deeper and con- 

 necting channel is filled with Drift, like those known to occur else- 

 where, beneath the lakes. Erom the straits, between the islands, 

 the narrow channel in Georgian Bay, just referred to, extends 

 south-eastward and is submerged to a depth of 510 feet. This is at 

 the foot of the Niagara escarpment, which extends, as a strong to- 

 pographic feature, from the head of Lake Ontario, and, rising in places 

 to 1700 feet above the sea, into the peninsula between Georgian 

 Bay and Lake Huron proper. The channels at the foot of escarp- 

 ments, submerged or otherwise, in Lake Huron and Georgian Bay 

 are fragmentary records of the history of the lake-valleys %. 



5. Features of Lake MicTdgan. 



This lake is divided into two basins. The more northern and 

 larger basin has a maximum depth of 864 feet. It is, in part, 

 bounded by vertical submerged escarpments, one of which, upon the 

 eastern side, has a height of 500 feet. Whilst the deepest sounding 

 at the modern outlet of the lake is only 2^2 feet, there are adjacent 

 channels buried to unknown depths. But these have been imper- 

 fectly explored. Into this shallower portion of the lake, however, 

 the fjord of Grand Traverse Bay has a northernly trend ; it is 

 612 feet deep. This and the lesser fjords indicate the existence 

 somewhere of a deep channel connecting with the Huron basin, as 

 much as the river-valleys buried beneath the Drift materials of the 

 modern floor of Lake Erie prove deep channels throughout that 



* See Eeports Geol. Canada, 1863-66. 



t See "Discovery of the Preglacial Outlet of Lake Erie," &e. 

 X See U. ^ Lake-Survey Chart of Lake Huron, and the Canadian Chart of 

 Georgian Bay. 



