versely with an imperfect conchoidal fracture, with a shining 

 resinous lustre, and sometimes yielding the appearance of 

 the markings of wood. This is the suturbrand of Iceland, 

 the Bovey coal of this country, and the common brown coal 

 of Thomson. 



The fossil wood, now described, may be said to pass 

 into Jet^ which is found, especially in the neighbourhood of 

 Whitby, in Yorkshire, in a state very nearly approximating 

 to that of Bovey coal. It exists in plates, generally from 

 half an inch to about an inch in thickness, between which a 

 film of carbonate of lime, with pyrites, is disposed : ex- 

 cepting that it more frequently shows marks oi ligneous 

 texture, its characters may be said to be those of jet: its 

 colour, velvet black ; internal lustre, shining, resinous ; 

 fracture perfect, large, conchoidal ; fragments, sharp edged, 

 soft, rather brittle ; easily frangible ; very light. Jet is 

 found in other situations, in a different form ; resembling, in 

 its shape, and the markings of its surface, parts of the 

 branches or trunks of trees, but rarely possessing, internally, 

 any marks of vegetable origin; a circumstance easily ac- 

 counted for, if its previous softening be admitted. 



Cannell Coal, of which some of the finest specimens are 

 found in Lancashire, differs from jet chiefly, perhaps, in its 

 holding a greater portion of earth in intimate mixture 

 with it. It never manifests internally any traces of vege- 

 table structure, but sometimes bears on its surface evident 

 marks of impressions formed on it whilst in a soft state. 



Common Coal is composed of a similar bituminous 

 matter, divided by films of calcareous spar mingled with 

 pyrites, intersecting each other nearly at right angles : its 

 fracture is thus rendered small grained, and uneven, and its 

 fragments mostly cubical or trapezoidal. By this division 

 and enclosure of the inflammable and bituminous matter in 

 incombustible septa, the accension and combustion of this 

 substance are rendered more slow, and better adapted to 



