Feather stonJiangh^s Geological Report. 115 



salt, and of course sufficiently porous to be pervious to water 

 These strata consist of porous, whitish-colored, fine-grained 

 sandstone, often tinged with a red color ; calcareous rocks of a 

 harder structure ; marly clays, containing particles of salt ; 

 and cavities, formerly containing large crystals. These general 

 characters seem to be common to all the borings. From the 

 general direction of the salt-works of this country an inference 

 may be drawn that these saliferous rocks run parallel to the 

 direction of the great bituminous coal field, and may, in fact, 

 constitute a mineral zone, saturated with salt, and conforming 

 in its general direction to other great mineral zones parallel 

 to it on the east. This is a subject highly deserving the most 

 accurate observation. The deeper the wells are sunk, the 

 stronger the brines arc found, probably on account of the ex- 

 hausted state of the rocks previously used. Generally speaking, 

 also, the brines only become gypseous at the greatest depths. 



Considering, however, the Alleghany or Backbone moun- 

 tain alluded to, near Shellburg, in Pennsylvania, as a great 

 geographical boundary separating the Western bituminous coal 

 measures from all the anthracite beds of the Silurian rocks, 

 running in a southwesterly direction to join the Cumberland 

 mountains, and having the salt deposites west of it, w^e find 

 some important salines east of this great boundary, as at Salt- 

 ville, near Abingdon, in Washington county, Virginia ; but 

 the floor of this valley, lying between Clinch's and Walker's 

 mountains, is the highly-inclined limestone found east of Han- 

 cock, in Maryland, alternating with shale, and carrying older 

 fossils than those which are found even in the carbonii'erous 

 limestone. The Abingdon wells, which i visited in 1834, are 

 in a totally diiferent deposite from those stony strata west of the 

 boundary just described. The valley in question has, before 

 the deposite of the salt, been much deeper than it is now, and 

 has been partly filled up by gypseous and saliferous clays. In 

 digging the first ten feet, they go through a blackish loam 

 which forms the surface of the whole valley, then twenty feet 

 8* 



