18 W. M. Fontaine— Geology of the Blue Ridge. 
tains enclosed fragments of argillites, sometimes little changed, 
and sometimes impregnated with chlorite, or with the minera 
owenite, which is one of the metamorphic associates of this rock, 
Width about three hundred feet. Traced from the bridge- 
head eastward, it is seen to pass gradually into unequivocal 
argillite, the quartz particles diminishing, and the base assuming 
more and more the Jaminated, slaty structure of the argillites. 
This portion of the argillites seems to have been involved in 
the upheaval of the mass, for it is cut up by joints into angular 
masses, much penetrated by irregular nests and seams of quartz, 
and is without bedding. A little farther east, just outside of 
this, we find a curious modification of the metamorphic rock. 
It here appears in the form of dykes, which thrust off the slates 
in arches. This rock is almost entirely composed of quartz, 
with a little of the amorphous matter present, which gives the 
stone a green color. Both this modification and the normal 
rock form an exceedingly tough and durable material, which 
by its indestructible nature has preserved the mountain from 
erosion. 
The above described rock, in weathered specimens especially, 
might be mistaken for a species of conglomerate think 
has been so described by H. D. Rogers, in his account of the 
South Mountains of Adams County, Pa. From the resem- 
blance of its base to a variety of Pinite, and for lack of a better 
name, I shall call it ‘ pinite porphyry,” although it is nota true 
igneous rock. Farther east we find argillites in heavy masses, 
penetrated with quartz, and leaning against the ridge with a dip 
of about 50° southeas 
To the west, up stream, for two miles to the east limit of the 
Silurian, we have normal argillites preserving a predominating 
southeast dip. Close to the pinite porphyry the slates are thrown 
into such abrupt flexures that they are rolled into cylindrical 
masses, which are penetrated by numerous quartz seams. More 
to the west ial | short rolls oceur, all denoting a thrust to the 
west on the part of the metamorphic rock. The line of junc- 
tion of the argillites with the Silurian is sharply marked, and 
no passage of one into the other occurs, although the southeast 
diate vicinity of the Blue Ridge. Quartzites of various natures 
