of some of the Principles of Vegetables into Bitumen , &c. 387 
5 11. 
The principal object I have in view, is to adduce some addi- 
tional proofs, that the bituminous substances are derived from 
the organized kingdoms of nature, and especially from vegetable 
bodies ; for, although many circumstances seem to lead to the 
opinion, that the animal kingdom has in some measure contri- 
buted to the partial formation of bitumen, yet the proofs are by 
no means so numerous, nor so positive, as those which indicate 
the vegetable kingdom to have been the grand source from 
which the bitumens have been derived. But this opinion, 
(founded upon very strong presumptive evidence,) although 
generally adopted, is however questioned by some persons ; and 
I shall therefore bring forward a few additional facts, which 
will, I flatter myself, contribute to demonstrate, that bitumen 
has been, and is actually and immediately formed, from the 
resin, and perhaps from some of the other juices of vegetables. 
The chemical characters of the pure or unmixed bitumens, 
such as naptha, petroleum, mineral tar, and asphaltum, are, in 
certain respects, so different from those of the resins and other 
inspissated juices of recent vegetables, that, had the former never 
occurred but in a separate and unmixed state, no positive in- 
ference could have been drawn from their properties, in proof of 
their vegetable origin. Fortunately, however, they have been 
more frequently found under circumstances which have strongly 
indicated the source from whence they have been derived; and 
much information has been acquired from observations made 
