NIAGARA.— I^EIITIAIIY STRATA ROUND PARIS. 217 



which the Niagara passes, below the falls, is nearly a mile wide with 

 almost perfect mural sides." — Transactions of the Albany Institute, 



In Mr. Loudon's Magazine of Natural History, March, 1830, 

 there is an account of the falls of Niagara, and of the physical 

 structure of the adjacent country, by my son, Robert Bakewell, jun- 

 ior. I preferred making the above extract from Mr. Henry's des- 

 cription, as it confirms the general accuracy of the drawing in the 

 frontispiece. Below will be seen a statement of the levels and the 

 extent of the North American lakes.* These lakes may justly be 

 styled seas of fresh water. Though their present surface is consid- 

 erably elevated above the level of the ocean, the bottom of some of 

 the largest lakes is much below the tide line ; and were these lakes 

 situated nearer to the Atlantic, we might easily imagine that after the 

 fresh water had subsided to the sea level, they might be subject to 

 frequent irrupdons of salt water, which would produce a change in 

 the nature of the inhabitants of these lakes; or, in other words, 

 would occasion alternations of marine with freshwater strata, without 

 any change in the relative level of the land and sea. 



In England and France, there appears to have been a considera- 

 ble interval between the deposition of the chalk, and of the lowest 

 beds of the secondary strata ; for the surface of the chalk is deeply 

 furrowed and broken, apparently by the action of torrents, or inunda- 

 tions, and the hollows filled by the tertiary beds. In some parts of 

 the Continent, however, the line of separation between the seconda- 

 ry and tertiary strata is not so distinctly marked, and they are»<b(^th 

 elevated together, conformably. ^ 



The tertiary strata form the outer crust of the globe, and have, 

 every where, been subjected to erosion from torrents and inundations, 

 that have swept over parts of its surface, and transported the frag- 

 ments into distant countries or into the ocean. We^cannot, from the 

 present localities of the upper strata, determine, with any precision, 

 the boundaries of the inland lakes or seas in which they were de- 

 posited. Many of these strata have, evidently, once extended far 

 beyond their present limits ; but have been so completely destroyed, 

 that we can infer their former existence, only by a few remaining 

 detached portions. 



* From Lake Erie to the falls of Niagara, the distance is 21 iniles. From the 

 falls to Lewiston, at the mouth of the chasm, the distance is 7 miles. From Lewis- 

 ton to Lake Ontario the distance is 7 miles. 



Elevation above Mean Length. Mean 



the sea. depth. breadth. 



Feet. Feet. Miles, Miles. 



Lake Superior - 641 900 300 80 



Lake Huron - 596 900 200 95 



Lake Michigan - 600 900 300 50 



Lake Erie - - 565 120 230 35 



Lake Ontario - 231 492 180 30 



Total quantity of square miles covered by the lakes. 72,930. 



28 



