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slates, impressed with vegetable forms, which you will there find 

 in great abundance. These you will frequently perceive to be so 

 perfect, that our sceptical friend Wilton will no longer be able to 

 hold out : he must, at last, give up the opinion, to which he has so 

 long, and so pertinaciously, adhered, that these are the productions 

 6f the wanton and fanciful sports of nature ; and must admit them 

 to have derived their forms from antediluvian vegetable remains. 

 With the hope of securing a convert, and of augmenting the plea- 

 sure which you must all experience, in the contemplation of these 

 wonders of nature, I shall, in this Letter, offer you a few observa- 

 tions on their origin and formation. 



In most of the strata which are found immediately above coal, 

 decided marks and impressions of vegetables may be discovered : 

 but it seldom happens, that any traces appear on the strata, on 

 which the coal lays. A considerable difference also exists, between 

 the several kinds of strata which lay immediately above coal, as to 

 the quantity of vegetables they contain, and the state in which they 

 are found. The strata which, most commonly, form the matrices 

 of these vegetable remains, are of the schistose kind ; sometimes of 

 a bluish grey colour, nearly verging on black; sometimes of a dark 

 brown, but most frequently of a jet black. In these schisti, the 

 impressions are often disposed as smooth and flat, as if the plants 

 had been carefully placed between the leaves of an herbarium. 

 Where this is the case, and the vegetable remains thus form a sepa- 

 rating medium of considerable extent between the laminae of the 

 schist, the complete separation of these laminae is easily effected, 

 by a small well-directed force ; and the impressions of the vege- 

 tables are thereby clearly displayed. 



The most beautiful specimens of this kind, are those, perhaps, 

 which are found in the coal-pits of Lancashire. Dr. Woodward 

 describes several fine specimens which he obtained from the Canel 

 coal-pits, near Haigh in Lancashire. The colliers there, he says, call 

 the substance on which they are formed black-baft : the colliers 



