ON BITUMENS, &C. JOQ 



tionable evidence, that bitumen has eflentially been produced 

 by the modification of fome of the proximate principles of 

 vegetables, and efpecially refin. 



Modern chemiftry had comparatively made but a ("mall pro- Whether they 

 grefs, when the illusions Bergmann publiftied his DiflTertation, be u ° f ] Z ncous or 

 entitled, Produ&a Ignis fubterranei chcmice confideruta ; for, attion. 

 that time, the extent and power of chemical action, in the 

 humid way, were very imperfectly underftood. In that part, 

 however, of the above work, where he fpeaks of the foffil 

 wood of Iceland, called Surturbrand, he evidently appears 

 doubtful how far volcanic lire may have acled upon it ; al- 

 though he conceives that, in the formation of it there has been 

 fome connection with volcanic operations. His words are, 

 " Quid de ligno fqffili ljlandite ftntiendwn fit, gnaro in loco na- 

 tali contemplaiori decidendum relinquimus. Interea, at cum 

 vidcani operationibus nexum credamus, plures fuadent rationes, 

 quantvU hucufque modion ignort?nus, quo fitum texturamque ad- 

 quifiverunt h&c jlrata." It certainly was very natural that 

 Bergmann fhouid entertain this opinion, in refpect to the fur- 

 turbrand ; and it is remarkable, that the leaves contained in 

 the fchiftus lately defcribed, are of the fame nature, and are 

 found in the fame country. The leaves alio defcribed by Mr. 

 St. Fond, are likewife found in a country which, according to 

 him, was formerly volcanic. Were thefe fubfiances, there- 

 fore, never found but in countries which either actually are 

 or were volcanic, we fiiould be almoft compelled to believe, 

 with the Swedifh profeflbr, that the operations of Subterra- 

 neous fires have been concerned in the formation of thefe 

 bodies, or rather in the converfion of them into their prefent 

 flate. 



But fimilar fubfiances are found in countries where not the They are found 



fmalleft veftige of volcanic effeas can be difcovered, and "? c ° u »t" e s evi- 



i ,i • r i i i r , dently not vol- 



Devonftiire moft undoubtedly is fuch ; yet, neverlhelels, the canix . 



Bovey coal is there found fimilar to the furturbrand, in rnofl: 



of the external, and (from experiments which I made fome 



years ago, I believe I may fay) chemical properties ; to which 



muft be added, that both thefe fubfiances perfectly refemble 



each other, by forming regular firata.* 



* Tranf. of the Linnean Society, Vol. IV. p. 138. Von Troil's 

 Letters, p. 42. OJiufcula Bergmanni, Tom. III. p. 239. 



Moreover, 



