THE DATE OF THE GLACIAL PERIOD. 587 



A further line of inferences follows from studying the 

 probable cause of the rise of the water in Lake Ontario dur- 

 ing the accumulation of the interglacial delta at Scarboro. 

 This, as we have stated, ^ as 150 feet, and the deposits at the 

 bottom indicate a warm climate, and those at the top a cold 

 climate. Now if ve study the conditions involved it will 

 appear that there is strong confirmation of the theory just 

 advanced. Evidently, as Professor Coleman points out. 

 the deposition of the Don beds began when the level of Lake 

 Ontario was just about what it is at the present time. That 

 would imply that its outlet was still through the St. Lawrence, 

 which must then have been unobstructed by ice. But as the 

 Labradorian ice advanced and closed up this outlet the water 

 level would eventually rise to the height of the col at Rome, 

 N. Y., leading through the Mohawk into the Hudson River. 

 This is 200 feet above Lake Ontario. But as it is shown that 

 now the axis of post-glacial elevation is the Mohawk Valley, 

 the north shore of Lake Ontario may well have been rela- 

 tively fifty feet higher during glacial times than it is now, 

 which would bring the elevation of the col at Rome into exact 

 harmony with that of the upper Scarboro beds. Under this 

 theory we have that gradual passage from warm to colder 

 conditions which we need to account for the change in species 

 in passing from the lower to the upper beds. And this is 

 just what Dr. Lamplugh has shown to be the case in the 

 glacial deposits of England.* 



2. The uniformity in the distribution of the till over the 

 southern portion of the glaciated area in the Mississippi 

 Valley is partly an illusion, due to the fact that the great 

 amount of loess covering the region, especially in southern 

 Indiana and Illinois and in eastern Nebraska, prevents, to a 

 considerable extent, observations upon the original surface, 

 and this loess, as has already been shown, is doubtless the 



* 'Presidential Address to the Geological Section of the British 

 Association for the Advancement of Science," at York, 1906. 



