on Bitumen in stones. 527 
bituminous and verifiable, agglutinate, and form substances 
resembling pumice, is a subject which may throw some light 
upon the natural formation of that substance. 
The conversion of obsidian into a species of pumice, and the 
proof that it contains bitumen, will probably be considered 
as supporting the mineralogical arrangement, which places 
that curious substance in connection with pitch-stone. 
As it appears from the facts here detailed that bitumen, or 
a volatile inflammable oil, exists in considerable proportion, 
and in chemical union, with all the rocks of the Floetk Trap 
formation, is it a far-fetched inference to consider that forma- 
tion as the chief source, whatever its own origin may have 
been, of the ejected volcanic products ? 
The appearance of an inflammable substance in the lower 
or elder rocks, such as mica, slate, &c. and, in particular, the 
exception in favour of colourless rock crystal and adularia, 
will probably obtain the attention of geologists. 
It is observable also, that in the last named rocks, the 
quantity of the volatile and inflammable ingredients is less 
than in the upper or more recent formations, and that it seems 
also to be more firmly united. 
If the scintillation of pulverised stones, when projected 
upon boiling nitre, be a test of their containing carbon, the 
experiments made with that object, demonstrate how much 
more generally that inflammable substance is distributed 
through the mineral kingdom, than was supposed ; and may 
account for much of the loss which the best chemists and most 
experienced manipulators are often obliged to acknowledge 
in their analyses. 
From these observations may it not be inferred, that no 
