232 THE CANADIAN NATURALIST. [Vol. X^ 



As the valley is five miles wide at this place, and as the well 

 is only about one mile distant from its southern side, it becomes 

 apparent that the valley in the centre must have been much 

 det'per. Moreover, if we produce the southern side of that 

 portion of the valley, which is over two miles wide, we find that 

 the well is less than a quarter of a mile away from it. Now if 

 we connect the top of the Medina shales (240 feet above Lake 

 Ontario) with the base of the drift in the well, and produce it to 

 the centre of the valle}', it wonld indicate a central depth of over 

 500 feet. At the base of the drift there are nearly fifty feet of 

 Medina shales, below which are the Hudson River rocks (more 

 or loss calcareous and arenaceous, mixed with the shales). 

 This harder formation alon^ the bed of a river would be less 

 extensively removed by aqueous action than the overlying Medina 

 shales, especially as the pitch of the waters would be much lessened. 

 This iiraphic method of calculation seems as perfectly admissible 

 here as it does in determining other constants of nature. How- 

 ever, I have placed the estimated depth in the section at about 

 70 fathoms below the lake surface, which depth is perfectly com- 

 patible with the soundings of the lake at no very great distance 

 to the eastward. Even this depth gives only very gentle slopes 

 from thcisides of the river valley. It should be remarked that 

 Burlington bay is excavated from stratified clays in places to a 

 depth of -78 feet. But this water is silting up comparatively 

 quickly. > 



Now we have seen that the deep excavation in the Dundas 

 valley and westward is cut through more than 250 feet of Niagara 

 and Clinton rocks, mostly limestone, and to a depth in the 

 Medina shales^, so that the total known depth of the canon is 743 

 feet, but with a calculated depth in the middle of the channel of 

 about 1000 feet. This depth for a ranoii is not extraordinary for 

 Eastern America. In Tennessee there are river valleys exca- 

 vated to a depth of U)00 feet. And in Pennsylvania Mr. Carll 

 reports others to be equally deep. 



Again»!this Preglacial river explains the cause of the present 

 topography of the western end of Lake Ontario. The drainage 

 by this river swept past the foot of the submerged escarpment of 

 Lake Ontario described in preceding pages, until it reached the 

 meridian of Oswego. 



With -such an outlet, and with the ancient Grand river 

 valley bnrif d by greater or less depth, we have an easy solution 



