196 THE CANADIAN NATURALIST. [Yol. viiL 



It will be necessary therefore to consider the bearings of this 

 fact on the course of the pre-glacial Mohawk. It is difficult, 

 perhaps impossible at present, to arrive at exact conclusions in 

 regard to its amount or its rate of increase northwards, but a 

 consideration of the phenomena presented by European and 

 American geology inclines us to assume that it was not exces- 

 sive, and that a rate of about three feet in a mile would not 

 vary much from the truth. With this estimate then we must 

 now calculate the effect of such an elevation on the various parts 

 of the bed of the river, and in so doing it will be sufficient for our 

 purpose to start from the mouth of the present Hudson River in 

 the harbour of New York in north latitude 40J°. The change 

 would place the western end of the Erie valley 645 feet above 

 the present Atlantic level, or 315 feet higher than now. But 

 the same change would elevate the Huron valley in lat. 45° to a 

 position 720 feet above the same level, and give a fall of rather 

 less than 100 feet from the latter to the former, making the flow 

 of the Mohawk not only possible but necessary. 



In the next place the bed of Lake Ontario lies nearly 500 feet 

 below that of Lake Erie, and as the change now in view would 

 not lessen this amount by more than 150 feet, it is evident that 

 no difficulty will be introduced to prevent the flow of the river 

 from the latter into the former, and it only remains therefore to 

 consider the relative levels at that day of the Ontarian valley 

 and New York harbour. The deepest part of the Ontarian 

 valley in lat. 43J° now lies, as we have said, at more than 200 

 feet below the surface of the Atlantic. The three degrees of 

 latitude between the two points correspond to an elevation of 

 630 feet. This would place the Ontarian valley about 400 feet 

 above the mouth of the Hudson, and supply ample fall for the 

 river in its course of about 400 miles between the two points. 



It must not be supposed that the figures above given are 

 strictly accurate, accuracy being unattainable in the present 

 state of our knowledge. They are only intended to show that 

 there is no difficulty, when all the facts and probabilities are 

 taken into account, in maintaining that in later Tertiary times 

 a pre-glacial Mohawk, greater than the present river, drained 

 the Huron valley and flowed through the gorge of Detroit into 

 the vale of Erie. Taking its course to the north-east it received 

 tributaries, among them the Maumee, the Rocky River, and the 

 Cuyahoga, and passed through a chasm not far from the present 



