Spencer.] 



306 



[Mar eh 18, 



merged Cambro-Siluriati (Hudson River, in part, if not throughout the 

 entire length) rocks, with its sloping summit, in part crowned by a gently- 

 sloping surface of Medina shales. Nearly north of the mouth of the Gen- 

 esee river we find that within a single mile the soundings vary from forty- 

 three to seventy-eight fathoms (between contour liaes). This gives a sud- 

 den descent in one mile of 310 feet. As the soundings are not taken con- 

 tinuously to show to the contrary, most of the change of levels may be 

 within a few hundred yards. 



In the region of these soundings the deepest water outside of the 78- 

 fathom line is 84 fathoms, while from the shore to the 43 fatliom sounding 

 the least distance is four and a half miles, thus giving the greatest mean 

 slope of the lake bottom at sixty feet in a mile, before the escarpment is 

 reached. 



An excellent series of soundings can be studied in a line nearly north- 

 ward from Pultneyville, N. Y. : 



Section ofLaAe Ontario from Point Peterlighf, Ontario, fyPutneyvilleXy. 



PtPeter. 



Distance Smiles. 



^uincyvillA 



From this table it will be seen that in a distance of less than two miles 

 the slope of the escarpment is the difference between 583 and 346 feet, or 

 386 feet as actually recorded. At Hamilton, the Niagara escarpment is 

 only 388 feet above the lake, which is two miles distant, whilst the present 

 slope at Thorold is spread over nearly twice that distance. That this escarp- 

 ment is: not local is easily seen. For a distance of over forty miles, from 

 near Oswego westward, it plunges down 300 feet or more in a breadth 

 varying from less than two to three miles. Eastward and westward of 

 this portion of the lake this submerged escarpment can be traced for nearly 



