1S6 ACCOUNT OF THE 



of this quarter has experienced no disruption, for it has cer- 

 tainly suffered no elevation nor bouleversement. It still re- 

 tains its horizontal position, or at most, varies from that in 

 too slight a degree to warrant the conclusion, unequivocally, 

 that the valley was formed either by an explosion and con- 

 sequent rupture of the strata, or by their subsidence. How 

 far their shrinking, from exsiccation, after being laid bare, 

 may have contributed to its formation. 1 am not prepared to 

 decide.* A hollow produced, however, by any of these 

 causes, except perhaps the last, would, I apprehend, be a 

 deep and irregular fissure, instead of a broad and shallow 

 trench, like that of the Ohio. 



To what agent, then, shall we ascribe this great excava- 

 tion? It is obviously impossible to answer this question 

 with certainty ; but it would not perhaps be rash to conclude 

 that, in its formation, there were two or three distinct and 

 successive stages or epochs. Some kind of channel and 

 some degree of declivity must have preceded the commence- 

 ment of every river ; but whether this and 



the other initial excavations were produced by unknown 

 causes which acted on the bottom of the sea, or by a violent 

 elevation of that bottom at the time of its deliverance from 

 the waters, I shall not offer a conjecture. Whatever may 

 have been the first agent, the second undoubtedly was the 

 vast and resistless currents that Fuust have attended the trans- 

 portation of the ocean from one bed to another. To tliese 

 currents, acting upon strata not yet perhaps fully consoli- 

 dated, and unsupported by the roots of a single plant, we 

 may fairly attribute most of the extent and form of the pre- 

 sent vallies. 



By supposing the change of place in the sea to have been 

 produced by the elevation of this continent, we can account 

 in some degree for those irregularities of surface which ori- 

 ginally directed the retiring waters into their present courses; 

 but the uniform levelness and extensive continuity of our se- 



• See Mr. Longraaire's Speculations in the Annals of Philosophy, Vol. 78. 



