ORDER II. BITUMINOUS MINERAL-COAL. 63 



fragments, when removed from its original repository, and 

 the low degree of lustre upon its imperfect conchoidal frac- 

 ture ; Common Brown Coal, which, though it still shews 

 traces of ligneous texture, is of a more firm consistency 

 than the rest of the varieties, and possesses higher degrees 

 of lustre upon its more perfect conchoidal fracture. Some 

 , varieties of Black coal immediately join those of Brown 

 coal. They are : Pitch Coal, of a velvet-black colour, ge- 

 nerally inclining to brown, strong lustre, and presenting in 

 every direction large and perfect conchoidal fracture. Slate 

 Coal possesses a more or less coarse slaty structure, which, 

 however, seems to be rather a kind of lamellar composition, 

 than real fracture. Foliated Coal is similarly compound, 

 only the laminae are thinner, and Coarse Coal has a compo- 

 sition resembling it, only the component particles are 

 smaller, and approach to a granular appearance. Cannel 

 Coal is without visible composition, and has a flat con- 

 choidal fracture in every direction, with but little lustre, 

 by which it is distinguished from Pitch-coal. It is most 

 like the Moor coal, but the difference in their specific gra- 

 vity is greater than between almost any other two varie- 

 ties of coal. All these kinds are joined by numerous transi- 

 tions, so that it often becomes doubtful to which of them 

 we should ascribe certain specimens, though they undoubt- 

 edly are bituminous Mineral-coal. 



2. The preceding varieties of coal consist of bitumen and 

 carbon in various proportions. They are more or less 

 easily inflammable, and burn with flame and a bituminous 

 smelL Several varieties become soft, and others coak, 

 when kindled. They leave a more ox less considerable 

 earthy residue. 



3. The varieties called slate coal, foliated coal, coarse 

 coal, cannel coal, and pitch coal, occur chiefly in the coal for- 

 mation ; some varieties of pitch -coal, also the moor-coal, 

 bituminous wood and common brown coal, are met with in 

 the formations above the chalk ; the earthy coal, and some 

 varieties of bituminous wood and common brown coal, are 

 often included in diluvial and alluvial detritus. The eoal 



