Geological Gleanings. 265 



of the Hudson must have been between 3000 and 4000 feet deep, 

 and it is probable that even the highest tops of the Catskills lay 

 below the water. 



" In Wales, it has been shown that during the emergence of 

 the country in the glacial epoch, the drift in some cases was 

 ploughed out of the valleys by glaciers; but though the Catskill 

 mountains are equally high, in the valleys beyond the great eastern 

 escarpment the drift still exists, which would not have been the 

 case had glaciers filled these valleys during emergence in the way 

 that took place in the Passes of Llanberis and Nant-Francon, and 

 in parts of the Highlands of Scotland. 



" It has been stated above that the upper plain around Lake 

 Erie, and the lower plain of Lake Ontario, are alike covered with 

 drift. Part of this was formed, and much of it modified during 

 the emergence of the country. In the valley of the St. Lawrence, 

 near Montreal, about 100 feet above the river, there are beds of 

 clay, containing Leda Portlaudica, and called by Dr. Dawson of 

 Montreal, the Leda clay. Dr. Dawson is of opinion that when 

 this clay was formed, the sea in which it was deposited wa?hed the 

 base of the old coast line that now makes the great escarpment 

 at Queenston and Lewiston, overlooking the plains round Lake 

 Ontario. It has long been an accepted belief that the Falls of 

 Niagara commenced at the edge of this escarpment, and that the 

 gorge has gradually been produced by the river wearing its way 

 back for seven miles to the place of the present Falls.* In this 

 case, the author conceives that the Falls commenced during the 

 deposition of the Leda clay, or near the close of the drift period, 

 when during the emergence of the country the escarpment had 

 already risen partly above water. If it should ever prove possible 

 to determine the actual rate of recession of the Falls, we shall 

 thus have data by which to determine approximately the time 

 that has elasped since the close of the drift period ; and an im- 

 portant step may thus be gained towards the actual estimate of a 

 portion of geological time." 



3. Sir Charles Lyell on the formation of Continuous Tabular 

 Masses of stony Lava or. steep slopes. — The question as to whether 

 volcanic cones have originated from the deposition of successive 

 sheets of the ejectamenta of their vents, or from the bulging up- 



* The details on which this belief is founded, may be found in the 

 writings of Professor Hall, of Albany, and Sir Charles Lyell. 



