by E.. Cornelius. 225 
The varieties, so far as I have observed, are quartz, horn- 
stone, flint, jasper, and semi-opal; and several, which to me 
are non-descripts. Quartz is the most abundant. It is found 
of different colors; compact, and porous or cellular ; of every 
size ; simple and associated with other silicious stones ; massive 
and crystallized. In Augusta and Rockbridge counties in Vir- 
ginia, beautiful crystals of quartz, are found; they are six- 
sided prisms, with double acuminations, that is, with six-sided 
pyramids, mounted on the opposite ends of the prism. A 
Specimen of two such crystals united, you have received. It 
was found near Lexingion. A curious variety of the quartz 
gravel-stone occurs on both sides of Elk River, a few miles 
above its junction with the Tennessee, in the Alabama ter- 
tiiory. As you travel to the west from Huntsville, it appears 
first in the neighborhood of Fort Hampton, two miles east of 
Elk River, and may be seen for ten miles west of that river.— 
The mineral is remarkable for containing a curious petrifaction. 
48 first appearance is that of a solid screw. On examination, 
however, you find it is not spiral; but consists of parallel con- 
_ Centric layers. Their diameter varies in different specimens, 
that of a pin to half an inch. They stand in the centre of 
a hollow cylinder, extending its whole length, and occupying 
about one-third of its dimensions. ‘The stone is sometimes per- 
fectly filled with these forms. The petrifaction I could not have 
famed, had you not pronounced it the “ Entrochite.” 
Hornstone, next to quartz, is the most abundant of the silicious 
minerals associated with limestone. It is very often seen im- 
bedded in rounded masses, both in the inclined and horizontal 
strata. 
Flint is more rare. Several fine specimens were observed on 
the western declivity of the Look-Out Mouftain, but in no in- 
in large masses or quantities. : 
Semi-Opal was found in one instance on the dividing ridge, 
~~ constitutes the southwestern boundary of the limestone 
8 
OF the non-descripts you have several specimens. One varie- 
‘ystrikes fire with steel, is of a milkwhite color, adheres slightly 
OL. I....No. 3. 3 
