-1830] 



WRITINGS OP JOSEPH HENRY. 



23 



than 200 feet below its surface, is composed of alluvial de- 

 posit, probably washed down from the upper lakes by the 

 continued action of a rapid current. Lake Ontario is ele- 

 vated 231 feet above the level of the ocean : its mean depth 

 has been estimated at 492 feet, although, in the middle, 

 attempts have been made with 300 fathoms without strik- 

 ing soundings.* The St. Lawrence river, which connects 

 this system of lakes with the Atlantic ocean, is the second 

 river in magnitude in America, being no less than ninety 

 miles wide at its mouth, and navigable for ships of the 

 largest size, 400 miles from the ocean: Its whole length, 

 from Lake Ontario to its mouth, is 692 miles.f 



The following table, compiled from Darby's Geographical 

 View of the United States, gives in a connected form, the 

 elevation and extent of the several waters of the St. Law- 

 rence basin. 



No. X. — Table of Elevation, mean Depth, Length, Breadth and Area, of the 

 several collections of Water in the great St. Lawrence basin. 



The several slopes of the St. Lawrence basin, not .covered 

 by water, have been estimated to be sufficient to sustain a 

 population of thirty millions of inhabitants. But the most 

 interesting fact connected with this great depression is the 

 vast quantity of fresh water contained in its several reser- 



*Dr. Bigsby's sketch of the topography of Lake Ontario. 

 Mag. and Annals, vol. 5, page 4. 

 t Darby. 



Philosoph. 



