176 M. R. CAMPBELL — PALEOZOIC OVERLAPS IN VIRGINIA. 



stone. The limestones are somewhat folded, and were evidently eroded 

 previous to the deposition of the conglomerate, for the surface upon 

 which the conglomerate was laid down is smooth and regular and cut 

 across the edges of the folded strata below. The conglomerate is com- 

 posed of yellowish white chalk-like matrix, in which are embedded peb- 

 bles of a character similar to the matrix. The pebbles are of various 

 sizes, from grains as large as the head of a pin to masses from six to nine 

 inches in diameter, and more or less rounded. In a few cases the smaller 

 grains are of foreign material, but the whole is so deeply decayed that 

 it is difficult to determine the genesis of the rock. In places it seems 

 like a subaerial deposit, while in others it appears like a true water- 

 deposited conglomerate. Its meaning is obscure, but the writer is of the 

 opinion that it indicates the existence of overlaps in early Paleozoic time 

 probably during the deposition of the Shenandoah limestone itself; that 

 the limestone was folded and elevated above sealevel and formed cliffs, 

 along which the masses and half rounded fragments washed from the 

 bank were recemented and formed these curious deposits of conglomerate. 



Silurian: Sevier (Hudson River) Shale. — But two exposures of this 

 shale are known to exist in the region. One of them lies south of Ingles 

 mountain, on the east side of New river, and is structurally a shallow, 

 faulted syncline of not more than three or four miles in length and half 

 a mile in breadth. In this area the formation consists essentially of cal- 

 careous shale, but with many thin beds or lenses of highly fossiliferous 

 limestone. In character these shales agree perfectly with the exposures 

 to be seen along New river northwest of the region in question, and were 

 obviously deposited under similar conditions ; but further west, along the 

 valley, the character is quite different, and certainly points to a different 

 origin and a different mode of accumulation. In the vicinity of Wythe- 

 ville there is a shallow basin, composed of sediments of the same age as 

 those already described, but very different in composition. These con- 

 sist almost entirely of soft felspathic sandstone or sandy shale, origi- 

 nally somewhat calcareous, but generally the calcareous matter has dis- 

 appeared through weathering and nothing but the- sand remains. This 

 phase does not reach Walker mountain on the northwest, and terminates 

 somewhere between Wytheville and Radford. The line marking this 

 change in character passes near the western extremity of this region 

 and probably constituted somewhat of a barrier between the two areas 

 of deposition. On the western slopes of Hamilton knob this formation 

 is supposed to outcrop, but nothing definite is known of either its char- 

 acter or the extent of its exposure. 



Bays (Red Medina) Sandstone. — This is also supposed to be present 

 on Hamilton knob, but, like the Sevier shale, was not studied sufficiently 

 to enable the writer to describe either the formation or its outcrop. 



