240 



TRANSACTIONS OF THE 



In order to give an adequate idea of the geognostic 

 situation of this cave and the surounding country, and 

 which, as we have already mentioned, stands in no rela- 

 tion with the subject of this memoir, we will communi- 

 cate an extract from a general geognostic description 

 which was contained in a report to the legislature of 

 Tennessee, delivered two years ago, and which we ex- 

 pect soon to oifer to the public. 



The lowest strata that prevail in Tennessee, west of 

 Cumberland mountains, are limestone, and are visible in 

 the vicinity of Nashville, and in some other counties. 

 These strata are composed of granular and compact lime- 

 stone of various shades of grey, from light ash grey to 

 blackish grey. They lie horizontally, and are charac- 

 terised by the following organic remains — several 

 species of orthoceratites, conotubularis, Bellerophon 

 hiulcus, isotelus, stromatopora : but particularly the Cala- 

 mophora gothlandica, and several species of terebratula, 

 spirifer and producti (which are all considered as cha- 

 racterising the upper transition series), are found in our 

 lower strata ; and there seems to be no doubt that they 



In the caves in which there is a constant current of air, as I have seen some 

 in the Smoky mountains, from the opening of which rushes always a current 

 of air, no saltpetre is formed. Could not this air furnish the constituents of 

 the nitric acid, which combines with lime and forms part of the saltpetre ma- 

 terials ? Besides we know from actual experiments, made first by Dr Priestley^ 

 and afterwards repeated by Cavendish, Gilpin and Davy, that when the elec- 

 tric fluid is made to pass through atmospheric air or any mixture of nitrogen 

 and oxygen, the two elements combine in the proportion to form acid. 



I believe it is easier to account for nitrogen in the production of nitric acid,, 

 than for the oxygen which it requires. We know that atmospheric air is com- 

 posed of from 21 to 23 per cent of oxygen, the remainder being nitrogen ; or 

 nearly, to take round numbers, as 1 of oxygen to 3 of nitrogen ; and nitric 

 acid is composed of 2| of oxygen to 1 of nitrogen. So that if all the oxygen 

 of the air combine.s with the necessary proportion of nitrogen to form nitric 

 acid, the remains of the air must be nitrogen gas, and of course we would find 

 an atmosphere in such caves not calculated to support animal life : and even 

 if the nitrogen was offered, by the decomposition of vegetable or animal mat- 

 ter, in a nascent state, to the atmosphere, it would make it unfit for respira- 

 tion. We must conclude then with saying, that the formation of saltpetre is 

 still surrounded with mystery. 



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