ee rr re er need 
J. L. Campbell—Silurian Formvtion in Virginia. 21 © 
between nee and Amherst Counties; while the north- 
west reaches about a mile beyond the crest of the North 
Mountain to the valley of rn Tockhbides Alum Springs, 
where it cuts the Devonian shales from which the waters of 
those springs flow. A subordinate ridge of Medina sandstones, 
however, rises in alle valley between the end of the section and 
the Springs. 
The first general division includes the metamorphic and 
eruptive rocks of the main Blue Ridge. The other general 
divisions are those adopted by eer Rogers in his surve 
of the State (1836-41). Only Nos. I to VII are includ 
The sub-divisions into which each ‘of Seooant is here divided are 
‘ may be regarded as representative (with local 
modifications), not only of the limestones of the Great Valley, 
There is no natural ae or gap ae the es th 
Ridge, but the 
pens has it been metamor = osed. This, with the aria 
beds of like ee OE Rate an 
and dipping in the opposite cektiens. lake sey esr No. I of 
¥; aleag gan sata It might be subdivided into 
very many alternations of sandstones and shales, but I have 
preferred to limit the number to seven, that are quite ogres 
in their general features for many miles along the N. 
of the range. At the grand natural section at Balcony alle 
where the James River passes through the mountain, about 
fifteen miles S.W. of my line, there is a very interesting expo- 
sure of all the divisions here given—similar in relative posi- 
tion, similar in lithological and fossil characters,~and having 
_ same general di 
bake e group, No. I, a, as a general rule, has a layer of 
feldspathic and siliceous conglomerate near the then 
