342 On the Secondary and Tertiary Formations. 
county, N.C. ‘The silica is the least injurious ingredient, its 
principal effect being, unless the rock is burned at too intense a 
heat, merely to render less sand necessary in tempering it for 
mortar, while the magnesia is not only of small quantity but 
doubtful tendency, and the oxide of iron is generally in too 
minute proportion to seriously injure the lime by giving it a very 
dark color. é 
Besides the lime that will hereafter add to the mineral wealth 
of this region, there is near Pocataligo, on navigable tide water, 
a deposit of the purest quality of quartz sand, suitable for the 
manufacture of glass. The pebbles of which it consists are 
small, sharp, angular-fragments of perfectly pure quartz, without 
any foreign mixture. It may be obtained in any quantity, and 
would probably pay for transportation as ballast under the cotton 
loads, either to the northern glass-houses or across the ocean. 
The locality is just half way between Charleston and Savan- 
nah, by the turnpike, on Mr. Spike’s plantation. saat 
- There is one more locality of the secondary limestone I vis- 
ited, which is near the Savannah river, in Georgia, at a place 
ealled Jacksonboro’.. The perfect similarity of the rock with 
that in Jones county, North Carolina, and on the Santee and 
Edisto in South Carolina, admits of no doubt that it is the same 
with them, and continuous through this wide extent of country: 
Even to the straw color of the rock, the brooks flowing out at 
its base, the lukewarm water, and the little shells that inhabit 
it, they are all nearly alike. This has been partially quarried, 
and the limestone burned. On opening the bed it is found to be 
about twelve feet thick, and within from the surface, the stone IS 
of a much whiter color, closely resembling chalk, aud appearing 
as if ithad already been burned. -'The heap.of rock in a hot 
southern sun presents so dazzling an appearance that one’s eye 
and head seriously suffer from closely examining the pieces 
They contain a great variety of fossil shells, affording most beau 
tiful specimens; but I have not succeeded in obtaining those F 
collected. A rude kiln has been constructed of the coarse san 
stone belonging to the same formation, and a considerable quau- 
tity of lime made. It is-very white and good lime, such proba 
Fas the: other localities described would afford, if worked a8 
extensively. It. is packed in boxes, which hold about threé 
