422 W. M. Fontaine—Primordial Strata of Virginia. 
west approach to the tunnel at Rockfish Gap. At a are the 
heavily-bedded slates of the mountain, while at 0 the thinly- 
laminated slaty shales, the lowest of the Primordial strata, are 
represented. 
In the two detailed sections given 
above at Balcony Falls and Rock- 
fish Gap I have been thus minute 
in my descriptions, in order that the 
reader may determine for himself 
how far the one confirms the other. 
e same time, the strata at the 
two places may be taken as types which best represent the 
normal and inverted positions, and also the changes which 
result from the different development of certain members of 
the series. 
Harper's Ferry. 
The exposures at this place are not sufficient to admit ofa 
detailed section. Enough, however, may be seen to show con- 
siderable changes. 
he argillites, described in a former paper, extend to the 
west about a mile and a half from the railroad bridge. e 
are then succeeded by the lower Primordial strata, the change 
being quite abrupt. The line of junction is well shown on the 
Virginia side of the Potomac, on the railroad. The massive 
dark gray beds of argillite are seen here, with a dip of about 
40° to the southeast, to abut against the highly imefined, more 
fragile lower Primordial strata. The change in the character 
of the rock is at once seen in the altered topography. The 
hills no longer present abrupt faces of firm rock close to the 
road, but recede with rounded slopes, which are so covered 
with earth and fragments of stone that it is difficult to find the 
strata in situ. The interval between the limestones of the 
Calciferous and the argillites is about 1,100 feet. These 
