1862.J 33 [Lesley, 



coal formation on the mountain^ throwing up a wedge of Lower Si- 

 lurian Limestone, as in the section, Fig. B. 



It is here that the relationship of these great faults to the normal 

 anticlinals and synclinals of the Appalachian region can be studied to 

 great advantage ; the presence of cross faults at high angles being 

 exhibited by the sudden termination of the mountains, and by the 

 tearing open, as it were, of one side of anticlinal coves. The sketch 

 of the topography north of Wytheville, in Fig. C, will show how 

 this has been effected, and render further description needless. 



The straitness of the mountains is sometimes interfered with by 

 small cross undulations or faults (it is not easy to determine which 

 they are), producing offsets and minute coves, notches, and some- 

 times gaps, as seen in Fig. F, representing a portion of the first pair 

 of mountains west of Wytheville. 



The " plaster banks" of the Holston, are deposits of rock salt and 

 gypsum and red marl, in excavations along faults, two of which are 

 transverse, and one parallel to the main fliult, at the foot of the Little 

 Clinch Mountain. Over this main fault the river flows, probably bury- 

 ing the outcrop of the coal, although it is possible that the fault 

 itself may here have cut out the coal, see Figs. E, h and c. Fig. E, a, 

 represents the coal, and the fault further east. 



These gypsum deposits have no geological connection with the 

 coal, however the analogy of the Michigan subcarboniferous gyp- 

 sum and salt, and of the Nova Scotia gypsum deposits, might seem 

 at first glance' to suggest one. They are found along the valley 

 for sixteen miles, but the principal deposit occupies the excavated 

 axis of a broken anticlinal, in the lowest part of the Lower Silurian 

 limestone. The plain of the Salt Works was once a triangular lake, 

 scooped out of the soft, reddish sulphur-iron rocks of the base of the 

 Palaeozoic system, lifted to the surface by an anticlinal, terminated 

 at its east or northeast end by a cross fracture, which lets the usual 

 hard limestones of the valley settle down on the other side of it into 

 their ordinary posture against the main fault. No plaster occurs above 

 water-level. The Upper Banks occupy a cross fracture ; and borings 

 here, 500 feet deep, bring up salt water. At the Middle Banks, seven 

 miles east of the Salt Works, the deposit seems to be on the line of the 

 main fault. A mile from the Salt Works, it is dug on the small cross 

 flxult. At the Salt Works, the borings go down along the snap of 

 the anticlinal, through 60 to 80 feet of plaster and red clay. 



The decomposition of the sulphurets in these red rocks, have con- 



