216 THE CANADIAN NATURALIST. [Vol. X. 



on the southern margin out of the Medina shales, and having its 

 southern shores from one to several miles from the foot of the 

 Niagara escarpment. The Medina shales form the western mar- 

 gin (where not covered with drift) to a point near Oakville. 

 From this town to a point some distance eastward of Toronto, 

 the hard rocks are made up of the different beds of Hudson River 

 epoch ; while the soft Utica shales occupy the middle portion, 

 and the Trenton limestone the portion of the Province towards 

 the eastern end of the lake. 



The country at the western end of the lake consists of slopes 

 gently rising to the foot of the Niagara escarpment, noticed before. 

 Sometimes this elevation is by terraces, and again by inclines so 

 gentle, as between Lake Ontario and the foot of the escarpment 

 at Limehouse (on the Gr. T. Railway) where the difference of 

 altitude above the water is more than 700 feet, without any 

 very conspicuous features. 



At the western end of the lake, the two shores converge at an 

 acute angle. At about five miles from the apex of this angle is 

 the low Burlington beach, thrown across the waters in a slightly 

 curved line, which forms the western end of the open lake. 

 Burlington bay, thus formed, is connected with the open lake by 

 a canal of the same name. This beach is made up of sand and 

 pebbles (mostly of Hudson River age), and is more than four 

 miles long, but nowhere is it half a mile wide. 



No mean depth of Lake Ontario can be fairly stated. For 

 geological purposes it has no mean depth, because it is simply 

 a long channel with the adjacent low lands covered by back- 

 water. 



West of the meridian of the Niagara river the lake is evidently 

 filled with more silt than eastward, as we find that the bottom 

 slopes more gradually towards the centre, where the mean depth 

 (increasing from the westward) of the channel may be fairly 

 placed at 400 feet below the present surface of the waters. In 

 this section of the lake, the average slope from both shores may be 

 stated at 30 feet in a mile. At a short distance east of the 78th 

 meridian, the character of the lake bottom changes in a most 

 conspicuous manner. Here we find a deeper channel which ex- 

 tends for more than ninety miles, having an average depth of 

 about 90 fathoms or 540 feet, with, in some places, a trough 

 about 600 feet deep, generally near the southern margin of the 



