some of the Principles of Vegcffahles into Biiiancn. 49 



as if thev had been subjected to an immense degree of 

 pressure*. 



The Bovey coal is connnonly of a chocolatc-brown, and 

 sometimes almost black. Tlic quality and texture of it arc 

 various in different strata : from s.onie of these it is obtained 

 in the form of straight Hat pieces, three or four feet in 

 length, resembling boards, and is therefore called Board 

 coal. Others have an obli(|ue, wavy, and undulating tex- 

 ture, and, as Dr. Millcs observes, have a strong resemblance 

 to the roots of trees, from which, most probably, this sort 

 has in a great measure been formed. 



Some kinds also appear to be more or less intermixed 

 with earth ; but that which produces the most powerful and 

 lasting fire is called stone coal : it is black, with a glossy 

 fracture ; has little or none of the vegetable texture ; is'more 

 solid and compact than the others, being almost as heavy 

 as some of the pit coals^ the nature of which it seems very 

 nearly to approach. 



For chemical examination I selected some of the coal 



* Bcrgmann, in the dissertation above quoted, accurately describes this 

 appearance of the surturbrand, and then says, " Quae autem immanis 

 rcquiritur vis, ut truncus cylindiicus ita coniplanetur ? Nor.ne antea 

 farticulaitmi nrxiis puhedijiis qiiodMn gradu fiicrit nelaxdtui ? Certe, nisi 

 compages quoviainmodo mtitatur, qi:odlibei pondus incumbens huic effec- 

 lui flit inipar. Cetcrum idem oD^crvatnr ptisnomenon in oviy.i schlsto 

 rj-gillaceo.' Tliii is certainly a very curious fact; and the learned Pro- 

 fessor, with liis usual acutfncss, rejects the idea that mere weight can 

 have been the cause. As a further proof alsa, he afterwards observes, 

 " Orthocerntitai, quae in stratv calcareo lonicomjrntratn perfcctc servant, 

 in sch'isw /'la/irmi frre triangidure ronij>yis;ionr ejp.ciioit. Idem valet de 

 ]ii:cii)US, conchis. insectisque petrefactis." And again, " Obsorvatu 

 quoque dignuiii est, quod idrvi rcperiatur rjr'ecius, quanivis stratum cal- 

 t ureuni fuh srhisio i olloatMU ;!t,rt majjriideo fiondvrc coniprnnciUe onusti/m." 

 De*Pyodatis Folcnniis, p. 440. It is c.idtnt, therefore, that weight 

 alone has not produced this tifcct ; and IJcrgmann's idea, that the soli- 

 ditv of the vcgetaLIc bodies may have uiidc'g'ine some previous change, 

 ill the maniiei of incipient putrc-f.tction, bv niMisture, and by becoming 

 heated in the mass, must be allowed to hi very probable. But bodies 

 such as shells could not be thus affected ; and therefore tliey must have 

 been exposed to some mechanical ctVect peculiar to argillaceous strata ; 

 which effect, however, from the circumstanci , which have been adduced, 

 evidently could not lijve resulted from the mere pressure of the supcr- 

 incutnbent strata. To me, therefore, it seems not very improb.ible that, 

 togi-ther with a cert-iin cinnge in the st)lidity of vegetable lodies, pro- 

 d'l.tJinthe manner imagined by Bergm.m!i, and, together with some 

 degree of superincumbent pressure, a real and powerful mechanical action 

 has been excited, by the contraction of the argillaceous strata, in conse- 

 quenre of dc>iccati.on j this, I believe, has not hitherto been itiuch con- 

 sidered ; but I am inclined, from many ciicuiiistances, to attribute to it a 

 very great degree of power. 



Vol . 2 1 . No. 8 1 . Fti. 1 805. D which 



