26 J. L. Campbell—Silurian Formation in Vurginia. 
falo Creek, six miles to the 8.W. N.W. of Lexington the out- 
crop of this bed is finely displayed along some parts of the base _ 
of Brushy Hills, and especially on the North River, a mile — 
o. III, 4, crops out extensively on both sides of Poplar _ 
Hills, forms the whole of the synclinal over which Lexington — 
stands,* and is the foundation rock of the House Mountains, _ 
around the base of which it may be seen re out on all 
sides. The general position here is horizontal, or nearly so, 
with some local curves. Northwest of Kerr’s Creek valley it © 
disappears beneath the North Mountain. & 
The general structure of 6 differs very widely from all the _ 
lower limestones—the s here, except some of the lowest, 
being thin layers of argillaceous limestones, with interstratified 
shales. Near the base of J, especially along its S.E. portion, 
underlying the Poplar Hills, we find a bed of very compact 
blue limestone irregularly bedded and very full of infiltrated 
veins; but, as we ascend, the rocks become more and more 
argillaceous, with the beds of shale becoming more numerous; __ 
and finally, as may be seen on House Mountain, after passing - 
upward through a thickness of about 650 feet, the shale 
becomes predominant, but still contains some thin beds of 
limestone remarkable for the profusion of fossil shells, crinoids 
and coral found in them. There is no well-defined horizon 
here, between what is represented on the section as b and c, but — 
the former seems in general characters to be the equivalent of 
the Trenton limestone, and'the latter of the Cincinnati (Hud- 
son) shales. It is about 750 feet thick. ; 
Remark.—I have not seen any outcrop of the division, a, of 
No. Ifl in Augusta county northeast of Staunton, nor have Ll 
seen it at all in Rockingham. [If its equivalent appears in that 
se of the valley, itis under quite different lithological and 
ossil peculiarities. I might say almost as much in regard to 
6; for limestone beds form a very inconspicuous part of UT, 
m Staunton (or rather a point S.E. of that place) to a point 
in Rockingham county, where it passes under iv in the Mas- 
sanutton range of mountains. - 
““FAULT.”—This seems to be the proper place for directing 
attention to the ‘‘ Fault,” the line of which passes in front (S.E.) 
of the House Mountain. It is easily traced for several miles _ 
. * This synclinal is really dowble—having a line of uplift ranning through it, but | 
the scale of the section would not admit its insertion. There are also some local 
tetebulariicce 3 : : : 
