J. L. Campbell—Silurian Formation in Virginia. 25 
The lithological and paleontological characters of this group 
of rocks, as well as its position seem to identify it with the 
ings that these lines indicate, for there are along the line many 
evidences of local warpings, fractures, dislocations, ete., that 
could not appear on such a section. Several trap-dykes are 
found protruded through the rocks of No. II, in Augusta and 
Rockingham counties, but none, so far as I know, in Rock- 
bridge. The Natural Bridge, from which this county takes its 
name, is in 6—being a portion of one of its upper strata span- 
ning a cajion or gorge, cut through its lower ale to a depth of 
more than 200 feet.* 
: —In some respects this group of rocks differs so 
widely here from its condition in Augusta and Rockingham 
counties, where Professor W. B. rs ee adopted it as typical 
e 
Lexington basin as a part of No. II, but I am equally confi- 
dent that he would, upon a more detailed eXamination, class 
JIL. 
(60) feet. It seems to run out somewhere beneath the syncli- 
nal fold that forms the Poplar Hills, but appears again on Buf- 
* T incline to the belief that this gorge was originally a crevice in the strata, 
and su by erosion—not the result of erosion alone; the arch 
having escaped fracture when the crevice was produced. 
