Mr. Maclure on the Geology of part ofj^. America. 99 



The utmost stretch of imagination or conjecture can form 

 no idea of any period of time, when that primitive chain of 

 mountains called the Alleghany, did not exist ; but direct 

 analogy, and perhaps logical reasoning, authorises us 

 to conjecture that there must have been a period, though 

 beyond the date of our records, when neither the alluvial of 

 the ocean, nor the Transition or Secondary depositions cov- 

 ered or overlaid either side of said range of mountains, and 

 that the chain of mountains called the AUeghanies stood alone, 

 and from the nature of the depositions which we npw find 

 covering each side, we may have a right to conjecture that 

 it was surrounded by water ; into which run all the rivers 

 that drained said mountains, forming channels deep io pro- 

 portion to the immense length of time they may have run, 

 and consequently much more profound than the channels 

 they afterwards wore in the level country at the foot of the 

 mountains on the retreat of the waters ; at this present time 

 all the waters that fall into that immense basin west of the 

 Alleghany mountains are drained off principally by the Mis* 

 sissippi and St. Lawrence, and a small part now by the 

 Hudson, although it is probable that formerly a greater pro- 

 portion used to pass by that channel ; these then are the 

 only rivers that break through the whole chain of the Alle- 

 ghany mountains, and run into the ocean. 



If on a review of any existing series of phenomena, it is 

 permitted to form conjectures on the past, and to look back , 

 on the probable changes, that may have preceded the pres- 

 ent state, we presume that the situation of this continent 

 will warrant such conjectures, and we should be naturally 

 led to suppose, that at some former period, the continuity of 

 the great chain of mountains was unbroken, by any of the 

 three rivers that now drain the great basin ; and that the 

 waters confined by the high surrounding ridge would form 

 an immense lake, the surplus of which would naturally fall 

 over the ridge into the ocean, and would in the course of 

 time cut those passages, which would drain said lake, and 

 leave the great interior basin, with all its. secondary or de- 

 position formation, as we now find it: as the waters that 

 would fall over the ridge into the sea, must have previously 

 left the sediments in the lake, there would be little or no 

 matter fit for alluvial depositions; and more probably that 

 great alluvial formation, from the bay ©f Mexico to Long- 



