OR UPPER BARRIER. 343 



some approach a horizontal direction, and others are 

 jumbled into confused heaps. The removal of sand, 

 gravel, and under-propping by rains, has in some in- 

 stances left the rocks in odd shaped piles ; and as these 

 shall be further deprived of support, they will quit their 

 present abodes, and rush precipitous to the valleys. The 

 road travelled by Braddock towards the fatal plains of 

 Monongahela in 1755, and the ground occupied by the 

 provisional army under Pinckney in 1800, are underlaid 

 by foundations of slate. 



Yet, in less than two miles, as you proceed up the Po- 

 tomac, limestone makes its appearance ; and you meet 

 with the like in travelling a few miles up the Shenandoah. 

 I am informed that shistus and quartz were heaped higk 

 in alternate and distinct strata, about ten miles hence, on 

 the banks of this latter river. 



Indeed it seems to me, as evident as the nature of the 

 case admits, that in Virginia as in New-York, slate under- 

 lays and supports the limestone. And it may be conceived 

 as in the highest degree probable, that the same material 

 which reaches to the foot of the Blue Mountains, on the 

 Virginia side of the Potomac, and on the Winchester side 

 of the Shenandoah, is continued beneath their elevated 

 ridges, and bears them on its back, as it does the Catskill 

 and the Newburgh mountains in New- York. Let the 

 geologists, in these parts of America particularly, study 

 the history of slate. 



The scenery about Harper's ferry is much and justly 

 celebrated. Several artists have attempted to paint it. 

 I recollect to have seen, several years ago, a picture of 

 it, by some person whose name I do not now remember, 

 in the Washington house at Mount Vernon. My atten- 



