ON BITUMENS, &C [ g J 



VII. 



Gbjervations on the Change of Joint of the proximate Principles 

 of Vegetables into Bitumen; with Analytical Experiments on 

 a peculiar Sn hfiance which is found with the Boz-ey Coal. By 

 Charles Hatchett, Ejq. F. R. S. From the Philojophi- 

 cal Transactions for 1 S04-. 



VJ'NE of the moll inftructive and important parts of geology, Converfion of 



is the ftudy of the fpontaneous alterations by which bodies. organ j z ^ bodies 

 e i . . , .,,., „ imo roflils. 



rormerly appertaining to the organized kingdoms of nature 



have, after the Iofs of the vital principle, become gradually 



converted into foffil fubftances. 



In fome cafes, this converlion has been lb complete, as to The degrees are 

 deftroy all traces of previous organic arrangement ; but, i n various * 

 others, the original texture and form have been more or lefs 

 preferved, although the fubftances retaining this texture, and 

 exhibiting thefe forms, are often decidedly of a mineral nature. 

 Some, however, of thefe extraneous foflils (as they are called) 

 retain part of their original fubfrance or principles, whilft others 

 "can only be regarded as cads or impreflions. 



From the animal kingdom we may felecl, as examples, thelnftances in the 

 foffil ivory, which retains its cartilage*; the bones in Gib- J™ 1 king ' 

 raltar rock, confilting of little more than the earthy part or 

 phofphate of lime; the fliells forming the lumachella of Bley- 

 berg, which ftill poflefs the luftre and iridefcence of their 

 original nacre ; and the Ihells found at Hordwell in Hamp- 

 fliire, and in Picardy, which are chiefly porcellaneous, but more 

 or lefs calcined; alfo the foflil echini and others, fo commonly 

 found in the limeftone, chalk, and calcareous grit of this ifland, 

 which, although they retain their original figure, are intirely, 

 or at leaft externally, formed of calcareous fpar, incrufling a 

 nucleus of flint or chalcedony. And if, in addition to thefe, we 

 may be allowed to regard the more recent limeftone and chalk 

 ftrata as having been principally or partly formed from the 

 detritus of animal exuviae, we fhall poflefs a complete feries 

 of gradations, commencing with animal fubftances analogous in 



* I have alfo found the cartilage perfe£t, in the teeth of the 

 mammoth. 



properties 



