of some o f the Principles of Vegetables into Bitumen , &c. 397 
for, as this is more immediately a chemical investigation, I wish 
to avoid, as much as possible, entering into any minute detail of 
geological circumstances. 
It mav however be proper to observe, that the Bovey coal is 
found in strata, corresponding in almost every particular with 
those of the surturbrand in Iceland, described by von Troil,* and 
by Professor Bergmann.'I* The different strata of both these 
substances are likewise similar, being composed of wood or 
trunks of trees, which have completely lost their cylindrical 
form, and are perfectly flattened, as if they had been subjected 
to an immense degree of pressure. J 
• Von Troil’s Letters, p. 42. 
f Opuscula Bergmanni, Tom. III. De Productis Volcaniis, p. 239, 
J B e r g m a n n , in the dissertation above quoted, accurately describes this appearance 
of the surturbrand, and then says, “ Quas autem immanis requiritur vis, ut truncus 
“ cylindricus ita complanetur? Nome anted particularum nexus putredinis quodam 
“ gradu fuerit relaxatus? Certe, nisi compages quodammodo mutafur, quodlibet 
“ pondus incumbens huic effectui erit impar. Ceterum idem observatur phenomenon 
“ in omni scbisto argillaceo.” This is certainly a very curious fact ; and the learned 
Professor, with his usual acuteness, rejects the idea that mere weight can have been the 
cause. As a farther proof also, he afterwards observes, f< Orthoceratitse, quae in strato 
“ calcareo conicam jiguram perfecte servant , in schisto planum fere triangulare com- 
“ pressione efficiunt. Idem valet de piscibus, conchis, insectisque petrefactis.” And 
again, “ Observatu quoque dignum est, quod idem reperiatur ejfectus, quamvis 
“ stratum calcareum sub schisto collocatum sit, et majori ideo pondere comprimente 
“ onustum .” De Productis Volcaniis, p. 240. It is evident, therefore, that weight 
alone has not produced this effect; and Bergmann’s idea, that the solidity of the 
vegetable bodies may have undergone some previous change, in the manner of inci- 
pient putrefaction, by moisture, and by becoming heated in the mass, must be allowed 
to be very probable. But bodies such as shells could not be thus affected ; and there- 
fore they must have been exposed to some mechanical effect, peculiar to argillaceous 
strata ; which effect, however, from the circumstances which have been adduced, evi- 
dently could not have resulted from the mere pressure of the superincumbent strata. To 
me, therefore, it seems not very improbable that, together with a certain change in the 
