so7ne oftJie Principles of Vegetables into Bitumen. 43 



many parts of this country, in which almost every appear- 

 ance of vegetable origin has been destroyed. 



The three exampli.-5 abovementioned appear to form the 

 extremities 2.ni}i centre of tlie series ; but as, from some local 

 circumstances, the process of carbonization and formation 

 of uitumen has not taken place in the first instance, and 

 as these eflects have proceeded to the ultimate degree in the 

 ]ast, it seems most proper that we should seek for inforn^a- 

 tion, and for positive evidence, in the second example, 

 which appears to be the mean point, exhibiting effects of 

 natural operations, by which bitumen and coal have been 

 imperfectly and paitially formed, without the absolute ob- 

 literation of the original vegetable characters; and, although 

 I have selected t'le Bovey coal as an example, because it^'is 

 found in this country, we must recollect that similar sub- 

 stances, or strata of bituminous wood, are found in manv 

 parts ui our globe; so that the example which has beeii 

 more immediately chosen is neither rare nor partial*. 



The nature, however, of the var'ous kinds of bituniinous 

 wood may in some respects be different : but this I have 

 not as yet had the means of ascertaining ; 1 shall therefore 

 only state the facts resulting from experiments made on 

 Bovey coal, and mere especially on a peculiar bituminous 

 substance with w hich it is accompanied. But, before I enter 

 into these particulars, it will be proper to mention a very 

 remarkable schistus with which I was, some months since, 

 favoured by the right honourable Sir Joseph Banks. 



§ in. 



This schistus was found by Sir Joseph, in the course of 

 his tour through Iceland, near Reykum, one of the ^reat 

 spoHting hot springs, tlistant about twenty-four English 

 miles froni Hafnifiord ; but circumstances did not permit 

 him to ascertain the extent of the stratum. 



The singularity of this substance is, that a great part of 

 it consists of leaves, which are evidently those of the alder, 

 interposed between the different lamella. I do not mean 

 mere impressions of leaves, such as are frequently found in 

 many ot the slates, but the real substance, in an apparently 

 half charred state, retaining distinctly the form of the leaves 

 and the arrangement of the fibres. 



The schistus is light, brittle, of easy exfoliation ; in UK- 

 transverse fracture earthy, and of a pale brown colour -, but, 



• SiMta of bituir-'nous wood nrc frond in various parrs of France, in 

 the vicinity of Cologne, in Hesse, Bohemia, Snx6nv, Italy, and especi- 

 ally ill ictlaud, where it it known under the name of juiiurbrand. 



w hen 



