of some of the Principles of Vegetables into Bitumen , &c. 407 
may thus be extracted from some of them, is petroleum. In 
these, the process of bituminization (if I may be allowed to 
employ such a term) appears to have been completed, whilst in 
the Bovey coal, and especially in the substance which accom- 
panies it, nature seems to have performed only the half of her 
work, and, from some unknown cause, to have stopped in the 
middle of her operations. But, by this circumstance, much light 
is thrown on the history of bituminous substances ; and the 
opinion, that they owe their origin to the organized kingdoms 
of nature, especially to that of vegetables, which hitherto has 
been supported only by presumptive proofs, seems now, in a 
great measure, to be confirmed, although the causes which operate 
these changes on vegetable bodies are as- yet undiscovered. 
Many facts indicate, that time alone does not reduce animal 
or vegetable bodies to the state of fossils. In this country, there 
are numerous examples of large quantities of timber, (even 
whole forests,) which have been submerged prior to any tradi- 
tion, and which nevertheless completely retain their ligneous 
characters.* Other local causes and agents must therefore have 
been required, to form the varieties of coal and other bituminous 
substances. In some instances, (as in the formation of Bovey 
coal,) these causes seem to have acted partially and imperfectly, 
whilst, in the formation of the greater part of the pit coals, 
their operation has been extensive and complete. 
In the pit coals, the mineral characters predominate, and the 
principal vestige of their real origin seems to be bitumen ; for 
the presence of carbon in the state of oxide, cannot alone be 
considered as decisive. 
• Phil. Trans, for January, 1671. Phil. Trans. Vol. XIX. p. 526. Ibid. Vol. XXII. 
p. 980. Ibid. Vol. XXIII. p. 1073. Ibid. Vol. XXVII. p. 298. Ibid, for 1799, 
p. 145. 
sG 
MDCCCIV. 
