232 



weight. Thus that which swims on water they describe as English, 

 but that which is heavier they suppose to be foreign. The grounds 

 of this distinction are, that the pieces of jet found on the English 

 shores are thus light, whilst the handsomer specimens brought from 

 France and Prussia are more ponderous : the fact, however, is, that 

 the pieces of jet found on our shores are also chiefly foreign ; and, 

 having been detached from the strata of the opposite shores, have, 

 in consequence of their lightness, floated here on the waves of 

 the sea. 



The transition of jet into c ANN EL COAL is frequently very diffi- 

 cult of detection ; the difference between the two substances seem- 

 ing to depend entirely on the quantity of foreign earthy matters 

 which have been introduced into the fluid bitumen. 



One mark of distinction between jet and cannel coal, perfectly 

 accords with the opinion which I have offered respecting their 

 formation. Jet, which is pure bituminized vegetable matter, some- 

 times, as has been already remarked, displays not only the general 

 form, but the texture and colour, of wood, manifesting that it is 

 purely bituminized wood, some parts of which, and these generally 

 the cortical, having resisted the influence of the fermentation more 

 than that part which is more generally considered as wood. But in 

 cannel coal, which has been in so fluid a state as to have admitted 

 the intermixture of earthy matters, seldom any thing of this kind 

 appears. Impressions of various vegetable substances are indeed 

 often displayed on its surface, possessing such a degree of correct- 

 ness and sharpness, as plainly to evince its having been in a very 

 soft state when the impressing substance was applied to it; but 

 these extend no deeper than the surface, its substance or texture 

 seldom pointing out the substance from which it originated. Re- 

 presentations of the appearances which thus offer themselves to our 

 yiewyou will see depictured, Plate 1. Fig. 6 & 7. 



Yours, &c. 



