364 W. M. Fontaine—Primordial Strata of Virginia. 
to the canal, slopes covered with debris. Hence details of the 
succession and dip of the strata cannot be given with accu- 
racy. 
A better exposure is given on the road mentioned above in 
Rogers’s description. Here, too, however, great confusion 
exists. By far the greater portion of the mass is composed o 
thinly laminated, gray and reddish shales. Some beds of 
brick-red and gray sandstones of coarse texture ovcur, much 
indurated, and sometimes impregnated with epidote, chlorite, 
etc. Also, one or two beds of diorite apparently. Probable 
thickness, 600 feet. 
To the west this is overlaid by a great series (10) of alternat- 
ing beds of quartzite and kaolin shales. These rocks, where 
they join (9), present the same contortions and confused stratifi- 
cation, but in passing farther west, the folds open out, and are 
finally seen well displayed in the high mountain through 
which the river cuts its way at the ‘Cement Mills.” 
This mountain is the most westerly of the parallel ranges 
which compose the Blue Ridge at this place. At its western 
base the James and North Rivers meet, and force a passage, 
exactly at the point of junction. We thus find here the same 
features as those presented by the Potomac and Shenandoah at 
Harper’s Ferry. 
Standing at the Cement Mills, just where the river issues ° 
from the gorge and in this first barrier, the perpendicular walls 
of the opposite bank are seen to be meena of beautifully 
regular arches of No. (10), piled one above another to a great 
height. Probable thickness, 700 feet. 
Both (9) and (10) seem, by a mighty thrust from the west, to 
have been crowded high up against the firm barrier — 
by the syenitic mass. This accounts for the gentle northwest 
dip which, as Prof Rogers correctly states, is shown by these 
upper strata in passing over the mountain to the east. In tak- 
ing the section along this road, I did not find this to be true 
of the lower strata up to No. (8). They, even near the top of 
the syenitic mountain, show the same high dip that is seen 
along the canal. The massive, unyielding plates of No. (8) 
seem to have protected them to a certain extent, but have 
themselves been extensively fractured. Hence, in passing 
along the mountain road from the mills to the east, we observe 
the following typographical features: oking westward, we 
see the strata of (10) rising and falling in rapid symmetrical 
undulations and forming the lofty range which fronts the valley 
of the river. Proceeding eastward, up the western slopes of 
the syenitic range, we pass first over the broken fragments of 
(10) and then of (9). Both, by the flattening out of the undu- 
lations, have a gentle northwest dip, and are partly crowded 
