468 THE CANADIAN NATURALIST. [Vol. vii. 



from the Dundas valley flowed into Burlington Bay till after the 

 cutting of the Desjardins Canal. About six miles east of this 

 ridge, Burlington Bay is separated from Lake Ontario by a low 

 beach about half a mile wide, consisting of sand and pebbles — 

 this being the present lake-shore. 



In several places, streams have made large deep gorges, through 

 the escarpment, some of which are more than half a mile long 

 and even 150 to 300 feet deep. The largest of these is known 

 as Spencer's Ravine. 



In the history of the superficial geology of this region there 

 are three distinct epochs : — during the first, the original excava- 

 tion of the Dundas valley, which has an area of nearly forty 

 square miles, took place ; the second epoch is that of the deposi- 

 tion of the Erie Clay and the partial filling of the valley; and 

 the third is that of the re-excavation of the valley, and the for- 

 mation of the lacustrine beaches and terraces. 



1. The original excavation of the valley of Dundas appears 

 to have been effected by means of the denuding action of a river 

 flowing from the west, forming a deep gorge, which widened 

 regularly as it approached the mouth, the part below the escarp- 

 ment being eight or nine miles in length, while at the mouth 

 the width was about six miles, — the whole somewhat resembling 

 the Niagara Biver between the Falls and Lewiston. The sides 

 had generally a straight course, broken occasionally by a second- 

 ary excavation in the solid rocks. The escarpment seems to have 

 had a higher elevation than at present, as the erosive effects of 

 the river had swept away the Medina formation to a depth 

 of more than 60 feet below the present level of the lake. 



2. The partial filling of the Valley by Erie clay was not much 

 under 200 feet in thickness, if it was uniformly deposited, as it 

 has a depth of 80 feet at Dundas, and on some of the higher 

 surroundings it occurs more than 100 feet above the present 

 lake- level, according to Prof. Bell. This clay frequently con- 

 tains boulders, partly of Laurentian age, and partly Palaeozoic. 

 It also overlies the Medina shales at Hamilton, and at Burling- 

 ton Heights is about 60 feet deep, all above, to the level of the 

 lake, having been swept away. The boulders have striated the 

 surface rocks of the Niagara formation (juite deeply in some 

 places, the direction of these not being constant ; just south of 

 Hamilton they are S. 55° W. This epoch was one of subsi- 

 dence. 



