238 Correspondence, 



Botanist for the Island of Trinidad, and a most skilful observer in 

 vegetable physiology, who, though originally opposed to the view 

 of the direct conversion of wood into bitumen, was obliged to jdeld 

 to the evidence of his own researches, as detailed in his descriptions 

 of the fossil plants collected during the survey, ' viz. " In nearly all 

 these specimens, or at least where there is a strong probability of 

 their representing wood in actual state of transformation into asphal- 

 tum, an evident parallelism exists with lignite." ...... "As the 



chemical process, which transforms wood into asphaltum, must be 

 very similar to that which changes it to lignite or coal, we conclude, 

 not too rashly, I think, in considering them to be in a transitory state." 



This view of the production of bitumen was never pretended to be 

 new, since Bischof showed, twenty years ago, that bituminous 

 substances are the result of direct conversion from wood and vege- 

 table remains, and adduced the chemical formula involved in the 

 process ; - but it was proved that the bitumens, so widely distributed 

 in Trinidad, and the adjacent part of South America, are positively 

 due to this cause, which operates under normal conditions of tem- 

 perature and climate ; not, perhaps, to be observed in a northern 

 country with an average temperature of 50°, but fully developed in 

 tropical latitudes with constant temperatures of 80° and upwards. 

 Such being the case, and every phenomenon relating to the bitumens 

 in these countries being easily explained according to this view, 

 and admitting of explanation according to no other view, why hesi- 

 tate to extend this origin of bitumens to other regions and other 

 conditions, where the mode of production of the oil, petroleum, or 

 pitch, may not be so susceptible of investigation or satisfactory 

 solution ? 



"With respect to distillation — in what instance can it be shown 

 that the bituminous matter of a carbonaceous stratum has been vola- 

 tilized by the proximity of heat and condensed at a certain distance 

 in other strata ? Experience rather teaches us that it would be en- 

 tirely dissipated or retained in the pores of the parent stratum in the 

 state of gas. The more or less bituminous nature of a coal seam does 

 not depend on its being in the latter case deeper seated, and nearer 

 the influence of heat ; since, as an instance in this district (South 

 Yorkshire), the most highly bituminous coal — the " Silkstone " — is 

 situated near the base of the series and 300 yards below the " Barns- 

 ley," or ''hard coal," distinguished by a very slight bituminous 

 content ; showing that the dry nature of a coal does not depend on 

 the separation of its bitumen by heat, but is due to the original 

 nature of the component vegetables, or to the nature of the minera- 

 lization experienced. Again, these natural bitumens, viz., pitch and 

 petroleum, do not correspond with the results of distillation, but are 

 precisely the products that would arise in the direct conversion con- 

 tended for. 



The production of bitumen from animal remains is not a part of 

 the question, which it is necessary to illustrate in this communi- 



1 Rep. Geol. Trinidad, Appendix K. 

 2 Chain, and Phys. Geol. Cavendish Soc. Trans, vol. i. pp. 288-291. 



