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LETTER XLVI. 
REMARKS ON LEAVES CONTAINED IN NODULES IMPRESSIONS OF 
THE SAME SIDE OF THE LEAF ON EACH NODULE ACCOUNTED 
FOR BY JUSSIEU, SCHULTZ, ETC EXPLANATION PROPOSED. 
I AM thoroughly aware of the circumstance to which our friend 
Wilton alludes. He desires you to inform me, that he will never 
believe the impressions on the two halves of the nodule he has sent 
me, are the impressions of a real leaf, until I can inform him if, by 
involving a guinea in plaster of Paris, I could obtain two impres- 
sions of the king’s head, without any impression of the reverse. 
The circumstance to which he refers has puzzled some of our most 
eminent lithologists. 
An instance of the erroneous opinions which have prevailed re- 
specting these subjects will be found in the remarks of our coun- 
tryman, Dr. Leigh*. “ In the rocks in these parts are only found 
Polypody, Wall Rue, Scolopendrium, or leaves of thorns ; doubt- 
less other leaves, as well as these, would have occurred to our 
observation, had these been deposited here by Noah s deluge. ^My 
sentiment of the whole is this, that as it is observable in chymistry 
that the salts of some plants will divaricate themselves into the 
figures of the plants, that these representations of plants in rocks are 
nothing but different concretions of saline, bituminous, and terrene 
particles.” 
* The Natural History of Lancashire, Cheshire, &c. by Charles Leigh, M.D. 1700, p. 99. 
