by E. Cornelius. 225 



The rarieties, so far as I have observed, are quartz, horn- 

 stone, flint, jasper, and semi-opal ; and several, which to me 

 are non-descripts. Qttartz is the most abundant. It is found 

 of different colours ; compact, and porous or cellular ; of every 

 size ; simple and associated with other silicious stones ; mas- 

 sive and crystallized. In Augusta and Rockbridge counties in 

 Virginia, beautiful crystals of quartz, of a singular form, 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 Lexington. A curious va- 

 riety of the quartz gravel-stone occurs on both sides of Elk 

 River, a few miles above its junction with the Tennessee, in 

 the Alabama territory. As you travel to the west from Hunts- 

 ville, it appears first in the neighbourhood 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. Its first appearance is that of a solid 

 screw. On examination, however, you find it is not spiral ; 

 but consists of parallel concentric layers. Their diameter 

 varies in different specimens, from 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 perfectly filled with these forms. The 

 petrifaction I could not have named, had you not pronounced 

 it the " Entrochite." 



Hornstone, next to quartz, is the most abundant of the sili- 

 cious minerals associated with limestone. It is very often 

 seen imbedded 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 Mountain, but in no 

 instances in large masses or quantities. 



Semi-Opal was found in one instance on the dividing ridge, 

 which constitutes the southwestern boundary of the lime- 

 stone strata. 



Of the non-descripts you have several specimens. One 

 variety strikes fire with steel, is a milk-white colour, adheres 



Vol. I. ...No. 3. 19 



