No. 2.] SPENCER — PREGLACIAL OUTLET OF L. ERIE. 77 



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 becoTiies 

 apparent that the valley in the centre must have been much 

 deeper. 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 con- 

 nect 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 valley, it would 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 less 

 calcareous and arenaceous, mixed with the shales). This harder 

 formation along the bed of the 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 graphic method of calculation seems as perfectly admissible 

 here as it does in determinins: 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 the sides of the river valley. It should be remarked that 

 Burliogton 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 of 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 canon is not extraordinary 

 for Eastern America. In Tennessee there are river valleys ex- 

 cavated to a depth of 1600 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, until it passed the meridian of Oswego. 



With such an outlet, and with the ancient Grand River valley 

 buried to an equal depth, we have an easy solution to the prob- 

 lem of the drainasie of Lake Erie. 



