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their solidity at the time of being impregnated with silex, have not 
allowed any diffusion of the matter, of which they were constituted, 
in the surrounding silicious fluid, which has merely penetrated and 
involved the bituminous fibres, and filled up all the interstices, with- 
out having been itself affected by the bitumen ; and into those, in 
which the bituminous mass has been in so fluid a state, as to have 
allowed its intimate mixture and union with the permeating lapidific 
fluid, which has thereby assumed, with other peculiar properties, a 
lustre similar to what might be expected from a mixture of silex and 
of bitumen. The species into which silicious woods may be divided, 
appear to be, 1st, calcedonic fossil wood ; 2dly, agatized ; 
3dly, jasperine ; and 4thly, opaline fossil wood. These several 
species we will now proceed to notice, in the order here observed. 
Yours, &c. 
LETTER XXXIV. 
CALCEDONIC WOOD AGATINE JASPERIZED. 
Calcedonic fossil wood appears to be the most simple form, in 
which silicized bituminous wood is found to exist ; and, therefore, 
serves to show, most clearly, the nature of the impregnation of 
solid bituminous wood with a solution of flint. In this wood, the 
colour and general appearance of which manifests very plainly its 
