of Kentucky and /frica. 147 
tive account of the nitre caverns, &c. of Kentucky, published 
in the Transactions of the Philosophical Society, in Philadel- 
phia, Vol. VI. and in Bruce’s Journal, Vol. I. p. 100. The 
following communication arose from a conversation on that 
subject, between Dr. Brown and the Editor. 
New-Haven, July 27, 1818. 
Dear Sir, 
Thave just found the passage I referred to the other day, 
relative to the existence of native or sandrock nitre in the 
interior of Southern Africa. It is in Barrow, and not in Vail- 
lant, as 1 thought when I had the pleasure of conversing with 
you concerning it. I am much obliged to you for recalling 
my attention to that curious subject, as it has brought to my 
recollection a fact, which I believe I omitted to mention in 
my memoir, (viz.) the existence of a black substance in the 
clay under the rocks, of a bituminous appearance and smell. 
This I remember to have seen in a rock-house, near the Ken- 
tucky river, where very considerable quantities of sandrock 
nitre had been obtained. This substance was found in masses 
of a few ounces weight, and in the crevices of the rocks near 
the basis of the side walls. The smell was not wholly bitu- 
‘™inous, but resembled that of bitumen combined with musk. 
Tam quite unable to account for the formation of the nitre, or 
Production of this black substance, which sometimes accom- 
Panies it both in Africa and America. Had I seen Mr. Bar- 
row’s travels, when I noticed the bitumen, I should certainly 
have paid more attention to it. But perceiving no relation 
between the rock nitre and the masses of this substance, my 
xamination of it was much too superficial. I do not very 
Well understand what Mr. Barrow means by saying, that many 
Wagon loads of animal matter lay on the roof of the caverns in 
Africa, I saw no such matter on the roof of the rock- houses 
. Kentucky. Certainly the caverns have been the habita- 
tions of wild beasts, and great quantities of leaves; &c. have 
been mixed with the debris of the superincumbent rocks, 
but it does not seem-probable, that much animal matter could 
be filtrated through a roof of rock, perhaps forty or fifty feet 
