Mr. Maclure on the Geology of part of JV. America. 1 1 



the small distance that the falls of Genesee river have 

 worn its bed from the lake, with the shallow beds of the 

 Oswego and all the other rivers that run into the lake, as 

 well as the general nature of all the Genesee country, op- 

 poses the probability of the supposition or conjecture. 



The above observations are equally applicable to the 

 beds of the Hudson and Mohawk, before they fall over the 

 ridge, from which it would appear that the most rational 

 conjecture would be, to suppose the St. Lawrence wore 

 down a passage through the high lands between Quebec and 

 Montreal, as well as the Hudson, through the high lands 

 above New-York, and until they had effected such a cut, 

 the whole basin on the west side of the mountains, was the 

 bottom of an Immense lake. 



A similar mode of reasoning supports the conjecture that 

 the basin of the Mississippi made part of the said lake, for 

 the Tennessee river, while in the mountains under the name 

 of the French Broad, has worn down its bed one hundred 

 to two hundred feet in solid primitive and transition 

 rocks, but when it comes into the basin, it is obstructed in 

 its passage, at the Muscle Shoals, by a soft secondary sand- 

 stone; the sources of the Ohio, under the name of New 

 River, &c. he. he. have likewise cut deep beds in the 

 mountains before they reach the great basin, but after their 

 union into one great stream, the Ohio is obstructed at its 

 falls near its mouth by a secondary limestone ; from all 

 which it would appear probable, that, had those rivers run 

 as long through the secondary formation of the great basin, 

 as their sources must have done to wear these beds so deep 

 in the primitive mountains, the accumulated waters of both 

 the Ohio and Genesee would, long ere this, have worn away 

 all the obstructing secondary rocks, and like all other great 

 rivers that have run long in the same beds, would have been 

 obstructed only by alluvion of their own formation. The 

 Rappahannock, Potomac, James River, Roanoke, &;c. he. 

 &;c. that run into the Atlantic, have cut deep beds in their 

 course through the mountains, through the level country 

 their channels are shallow, and they all fall from twenty to 

 thirty feet over the granite ridge into tide water, without hav- 

 ing removed, the fall half a mile from where they begun, 

 which could not have been the case had they run as long in 

 the low country, as they had in the mountains. 



