W. M. Fontaine—Geology of the Blue Ridge. 19 
appear along the eastern border, and form the Catoctin to the 
southwest. These rocks in the north are the micaceous, slaty 
quartzites which form the Bull Run Mountains. To the 
c 
Ridge near Swift Run Gap. Commencing on the east of the 
Catoctin range, we have the following rocks: 1st, Limestones, 
2d, quartzites, and 384, epidosites. These are usually associated, 
and the second form the mass of the Catoctin. These mountains 
in this region are usually composed of quartzites, while the lime- 
stones occur to the east of them. In the valley we find that 
from east to west Steatites, hydromica slates, mica* slates, mica 
schists, and gneiss appear in the order named, so as to usurp the 
This change may be due partly to the fact that the argil 
lites, which seem to be the source of the epidotic and chloritic 
roducts, 
reason to think that the quartzites and associated rocks overlie 
the argillites here; hence the disappearance of the latter rocks. 
Vv Retry the metamorphic pro- 
ducts are principally quartzose. The case is different to the 
* T have in this article used the terms mica slate and mica schist to denote dif- 
e 
ferent rocks, ormer has slaty cleavages, is thinly laminated and fragile, 
“ving an amorphous to sub-micaceous texture, with a ion almost wholly 
— f micaceous matter e mica schists are stronger, heavier-bedded rocks, 
eerily. ous matter in about equal proportions, and both appearing 
in visible individual particles, Itis noteworthy that in no case is ei 
teas ait 
that of the region adjacent to the Richmond granite, where both quartz and mica 
large particles and produce a rock much like the mica schist of New York 
