45 Olservations on the Change of 



positive, as those which indicate the vegetable kingdom to 

 have been the crand source from which the bitumens have 

 been derived. But this opinion (founded upon very strong 

 presumptive evidence), although generally adopted, is how- 

 ever questioned by some persons ; and I shall therefore 

 brino; 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, 

 5uch as naptha, petroleum, mineral tar, and asphaltum, are, 

 in certain respects, so diflercnt 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 inference could have been drawn from their 

 properties in proof of their vegetable origin. Fortunately, 

 however, they have been more frcquentlv foimd under cir- 

 cumstances which have strongly indicated tlic source from 

 whence they have been derived ; and nuicli information has 

 been acquired from observations made on the varieties of 

 turf, bituminous wood, and pit coal, on the nature of their 

 surroun-ding strata, on the vestiges of animal and vegetable 

 bodies which accompany them, and on various other local 

 facts, all of which tend considerably to elucidate the history 

 of their formation, and to throw light upon this interesting 

 part of geology. 



Some instances have already been mentioned which 

 show that lossil animal substances form a series, com- 

 inencing with such as are scav<xlv different Irom those 

 which are recent, and terminating in productions which 

 have totally lost all traces of organization. 



Similar instances are afforded by the vegetable, kingdom ; 

 l)ut, without entering into a minute detail of every grada- 

 tion, I shall only cite three examples in this island, namely, 



1. The submarine forest at Sutton, on the coast of Lin- 

 colnshire, the timber of which has not suffered any vcrv 

 apparent change in its vegetable characters*. 



2. The strata of bituminous wood (called Bovey coal) 

 found at Bovev, in Devon ; which exhibits a series of gra- 

 dations, from the most perfect ligneous texture, to a sub- 

 stance nearly approaching the characters of pit coal, and, 

 on that account, distinguished by the name of stone coal. 



3. And lastly, the varieties of pit coal, so abundant in 



* Account of a subrr^arine, Forest on the East Coast of England, by 

 Dr. Coma de Serra, Pi.iJ. Trans, for 1799, T- ' t-j- 



