218 Geology, irc, of Tennessee, <$/•<;. 



ghany ; and constitutes one of the most prominent features in 

 the geology of the United States. Its height I cannot deter- 

 mine with accuracy. Probably it would not average more than 

 one thousand feet. Its base may extend in diameter from one 

 to two miles ; and yet such is the influence it has on the cli- 

 mate, that vegetation on the eastern, is usually two weeks ear- 

 lier than on the western side. And what is remarkable, this 

 difference obtains, on the former side at least, until you arrive 

 within a few hundred yards of the summit. I crossed the 

 mountain in two places, distant from each other one hundred 

 miles, but observed nothing essentially different in their mine- 

 ralogy. At one of them called the Rockjish-Gap, on the road 

 from Charlotteville to Staunton, I spent afew hours, and brought 

 away specimens of all the varieties of minerals which I could 

 find. These have been submitted to your inspection. Among 

 them, you will, I think, see greenstone, epidote, and slate more 

 or less allied to the first. These are the most common rocks, 

 and excepting the second, are usually stratified. The epidote 

 is generally associated with quartz, and sometimes is imbedded 

 in it. In some instances it has a porphyritic appearance, and 

 is very beautiful. In others, it is coated with small filaments 

 of a greenish asbestos. Other minerals were found, whose 

 nature I could not so easily determine. I regret exceedingly, 

 that I cannot furnish you with a more complete description of 

 this interesting mountain. That its character is peculiar, or 

 different from the country on either side of it, must be obvious 

 to the most superficial observer. Its principal rock does in- 

 deed bear a resemblance to the trap or whinstone of Albe- 

 marle county, and yet I think you will say it is not the same. 

 One fact of importance cannot be mistaken ; this mountain con- 

 stitutes the great dividing line between the granite and lime- 

 stone countries. For you no sooner reach its western base, 

 than the greenstone and epidote disappear ; and limestone per- 

 vades the country for hundreds of miles in every direction. In 

 all the distance from this mountain to New-Orleans, I did not 

 find a single specimen of granite, or greenstone. This may 

 appear singular, since Mr. Maclure and Professor Cleaveland 

 kave a granite range on their maps, immediately west of the 



