Geology of the Virginias. 197 



eastern border of the great coal-field ; but the lower division, 

 13 a, is especially worthy of notice, as it is here a real coal- 

 bearing formation. At the date of Professor Rogers's Reports, 

 (1835-41), it promised to be of great economical importance 

 to the State, on account, first, of the intrinsic value of much of 

 the coal found in it ; secondly, of its proximity to extensive 

 beds of iron ores, and to points in the general market ; and 

 thirdly, of the fact that the eastern portion of the State was, at 

 that period, cut off in a great measure from the coal-field west 

 of the Alleghany range, by want of lines of transportation. 

 But since several railway lines have brought the products of 

 the richer and more available mines into competition with 

 those that are less productive, and more expensive to work, 

 very little mining has been done except to meet demands for 

 local consumption. 



Although this limited field has ceased to have any great 

 commercial value, it still possesses a scientific interest from its 

 relations to the salt-wells on the Holston and the Kanawha 

 rivers. 



The history of geological investigations and speculations 

 regarding the origin of the beds of gypsum and salt, found in 

 the valley of the north fork of the Holston, in Washington 

 county, is both interesting and instructive. The problem of 

 the true geological relation of these minerals has for a long time 

 been under discussion. Traversing the little river valley in 

 which they are found is a remarkable line of faulting, by which 

 the beds of Sub-carboniferous, 13 a, b, have dropped down on 

 the northwest side, or the Canadian limestones of 3 b, c, have 

 been thrust upward on the southeast side, to such an extent that 

 the two formations are now on the same level, although at other 

 points, where they still retain their normal relations to each 

 other, they are several thousand feet apart. 



Near this line of dislocation, beds of gypsum, in rather irreg- 

 ular concretionary masses, have been opened and mined at a 

 number of points over an area of several square miles. Within 

 this general area a number of salt-wells have been sunk, pene- 

 trating beds of rock-salt of considerable thickness. From the 

 strong brine of these wells salt has been manufactured for many 

 years. 



As to the gypsum, all agree that it was once corbonate of 

 lime, changed now to sulphate by the action of sulphuric acid 

 from the adjacent pyritous shales, but there has been a differ- 

 ence of opinion as to the age of the limestones from which the 

 gypsum was produced. . In relation to the source and mode of 

 accumulation of the salt beds, there has been a like diversity of 

 opinion. Prof. Rogers himself seems to have greatly modified 

 his views of this region at different periods in the history of his 



