16 W. df, Fontaine—Geology of the Blue Ridge. 
miles between Point of Rocks and Harper’s Ferry. It forms 
also the most of the Blue Ridge at the latter place. Through- 
out this entire distance this rock shows a high southeast 
dip (45°), and evidently lies in a series of closed folds. The 
following is the normal character as presented throughout the 
district: Texture, fine, amorphous, to sub micaceous; color, 
dark gray, sometimes greenish, from films of chlorite. Cleavage 
usually obscured by consolidation, but parallel to the bedding. 
It occurs in more or less massive layers, often cut by joints, and 
is usually harder and denser than ordinary roofing slate. At 
Point of Rocks the following modifications are seen : 
ommencing at the east entrance of the tunnel, we have the 
scales. Pyrite is quite on. This central, highly altered 
portion, has plainly been sufficiently softened to be capable of 
motion like a fused has been thrust up along the 
again, these are thrown into abrupt sigmoid flexures, indicating 
such a motion of the central mass. 
I have little doubt but that this peculiar effect is due to the 
erushing of the beds in the center of a synclinal fold. But the 
existence of a closed synclinal alone will rot account for the 
and lines of weakness of great extent in the direction of these 
mountains; for we find in them true igneous rocks also, espe- 
cially in the Blue Ridge. 
The rocks occupying a belt of two and a half miles in width, 
on the west of the Catoctin, exhibit along one or two lines the 
same features of metamorphism that are to be seen at Point of 
Rocks, but on a smaller scale. In each case we find this in- 
crease of local change along certain belts to be marked by 
ranges of hills commanding the country around. The Catoctin 
