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LETTER XLI. 



VARIETY OF PETRIFIED WOODS. ...PROCEEDING FROM ORIGINAL 

 NATURAL DIFFERENCE. ...FROM THE LABOURS OF MAN. 



1 HE resemblance between the recent and fossil woods is some- 

 times very close, with respect to colour. The bituminous willow, 

 found by Capt. Perry, near Dagenham-breach, he describes, as hav- 

 ing suffered little or no alteration in its colour; and, in a specimen 

 resembling mahogany, and in various others, now before me, there 

 appears to be the strongest reason for supposing, that, from the 

 absence of certain mineral or saline 'agents, the bitumen has retained 

 the colour of the vegetable substance, to which it was indebted for 

 its origin. 



So perfectly do the masses of petrified wood sometimes retain 

 the characters which belonged to them in a recent state, that it 

 frequently happens that, although so considerably changed in their 

 naturr, it is not difficult to determine to what species of wood the 

 petrified mass originally belonged. Thus, in Plate II. Fig. 4, and 

 Fig. 5, is a specimen which bears an exact resemblance to a piece 

 of deal, which, having split at one end, has had the rifts, thereby 

 occasioned, filled up by a dark coloured bitumen, as is depicted in 

 Fig. 4 ; and which, as is shown in the section of the same piece, at 

 Fig. 5, has insinuated itself to a considerable depth into the sub- 

 stance of the wood. Volkman describes a similar specimen, as 

 having a black crust, like resin or pitch ; and which he supposes to 

 have been the resin of the fir or pine ; which had been caused thus 

 to exude, by the influence of subterranean heat. The "fir, which in 

 a petrified state is known by the terms Elatites, Peucites, and Li- 



