1881.] 0\)i [Spencer. 



one hundred miles, but with the portion deeper than the 70-fathoni con- 

 tour having more gradual soundings, as the base of the hills either origi- 

 nally had a more gradual slope, or the lake in its western extension has 

 subsequently been filled with more silt. 



Although we have not soundings made very close together, yet the 

 admirable work of the United States Lake Survey is more than sufficient to 

 prove the existing of a continuous escarpment that has an important bear- 

 ing on the Preglacial geography of the region, and on the explanation of 

 the origin of the Great Lakes themselves. 



The soundings do not show a conspicuous escarpment after passing west- 

 ward of the meridian of Niagara river, partly on account of the sediments 

 filling this portion of the lake, and partly because the lake in all proba- 

 bility never had its channel excavated to so great a depth as farther east- 

 ward. 



Attention must be called to the fact that the depth of the Niagara river 

 is 12 fathoms near its mouth, but that the lake around the outlet of the 

 river has not a depth exceeding four fathoms with a rocky bottom. 



Another escarpment at the level of Lake Ontario, now buried, was dis- 

 covered by the engineers of the enlargement of the Welland canal, accord- 

 ing to Prof. Clay pole (Can. Nat. Vol. ix. No. 4). When constructing. No. 

 1 lock, at Port Dalhousie, it was found that at its northern end, there was 

 an absence of hard rock which formed the foundation of its southern end. 

 Kods more than 40 feet long were pushed into the slimy earth without 

 meeting any hard rock bottom. This discovery will be noticed in the 

 sequel. * 



Basin of Lake Erie. The exceedingly shallow basin of Lake Erie has its 

 bottom as near a level plane as any terrestrial tract could be. Its mean 

 depth, or even maxima and minima depths from its western end for more 

 than 150 miles, scarcely varies from 12 or 13 fathoms for the greater por- 

 tion of its width. The eastern 20 miles has also a bed no deeper 

 than the western portion. Between these two portions of the lake, 

 the hydrography shows an area with twice this depth (the deepest 

 sounding being 35 fathoms). This deepest portion skirts Long Point (the 

 extremity, a modern peninsula of lacustrine origin), and has a some- 

 what transverse course. An area of less than 40 miles long has a depth 

 of more than 20 fathoms. The deeper channel seems to turn around Long 

 Point, and take a course towards Haldemand c®unty, in our Canadian 

 Province, somewhere west of Maitland. The outlet of the lake, in the di- 

 rection of the Niagara river, has a rocky bottom (Coniferous limestone). 



The study of this lake at first appears less practicable than that of 

 Ontario, but, when its former outlet and its tributary rivers are described, 

 the writer trusts that he will have made some observations, that may help 

 to clear the darkness that hangs about the history of our interesting lake 

 region, before tlie advent of the Ice Age. 



The Dundas Valley and adjacent Canons. We may consider that the 



* See Report of Chief Kugineer of Canadian Canals, 18S0. 



PROC. AMEK. PHILOS. SOC. XIX. 108. 2m. PRINTED MARCH 30, 1881. 



