W. M. Fontaine—Primordial Strata of Virginia. 428 
ciferous. These rocks, in their upper or more westerly portion, 
are succeeded by a highly-altered sandstone of brownish color 
and rather coarse grain. About forty feet of this are shown. 
It lies in rather thin lamine, and has the same dip with the 
pose No other strata were seen until the Calciferous 
imestone, distant one or two hundred feet, was reached. This 
latter series also shows important modifications. The entire 
thickness of the strata lying below the Calciferous at Harper's 
erry cannot be much over 1,000 feet. So far as seen, only two 
varieties of rock occupy this space, viz: the slaty rocks above 
mentioned, which form by far the largest portion, and the sand- 
stone, which much resembles some of the quartzites of the lower 
strata at Rockfish Gap. It will thus be seen that, along with the 
greatly diminished thickness of the formation, the disappear- 
ance of most of the coarser material seen to the southwest is to 
be noted here. It is not impossible that some of the beds have 
been engulfed in their upheaval, since on the Virginia side the 
manner in which the argillites abut against the Primordial in- 
dicates that the former were crowded in a solid mass over 
against the latter. 
he Calciferous rocks at this place are almost entirely lime- 
stones. Instead of the numerous alternations of shale and im- 
ure limestone, which elsewhere form the lower beds, we have 
stratified. The lamin stand at an angle o 
able deposits of iron ore. The excavations made on the 
Maryland side of the Potomac for the procuring of the ore 
have well exposed its character. It lies immediately to the 
west of the rock last described. From the examination made 
in the open cuts in the iron mine about two miles above the 
bridge, its character seems to be as follows: color dark gray, 
fracture rough and glistening, from its sub-crystalline texture. 
e hardness and weight are much above those of ordinary 
pure limestone. It lies in masses of the thickness of thirty feet 
and more, without bedding. Without close examination, it 
would be mistaken for a variety of igneous rock. The ore is 
an argillaceous limonite, occupying a seam varying in width 
