455 



tained the name of petrified mushrooms : nor could the petrifaction 

 of funguses produce a nearer resemblance to mushrooms than these 

 substances present. They are frequently found in the cliffs in Dor- 

 setshire, and other parts, and appear to have been formed by the 

 gradual oozing of a soft ferruginous clay, strongly impregnated with 

 pyrites, from small openings in the rocks. 



Yours, &c. 



LETTER XLVIIL 



CONCLUSION. 



ENDEAVOURED, in the early part of our correspondence, to lay 

 before you the opinions which were formerly entertained, respect- 

 ing the substances which have been generally known by the name 

 of extraneous fossils ; and also to give you a slight sketch of the 

 history of the discoveries which have been made, concerning their 

 nature and origin, we then entered upon an examination of such 

 substances as appeared to be best designated by the term vege- 

 table secondary fossils. A strict examination of these seemed to 

 render it manifest, that their formation depended on a certain law 

 of nature which decrees, that such vegetable substances as become 

 buried so deep, as to prevent their being directly useful to man, 

 either as timber, or as soil fitted to aid the growth of other vege- 

 tables, should undergo certain other changes, by which they should be 



