22 



stices filled with nearly colourless spar. The lime being 

 removed from this fossil by muriatic acid, a considerable 

 portion of light-coloured flocculent substance is deposited. 

 Found in alluvia and in the oolite formation. 



2. Calcareous spathose wood, previously bituminized. — 

 Colour darkish red brown ; surface commonly rough, but 

 partially glossy ; fracture dull, uneven, and rather spicular, 

 veined with spar of a lightish brown colour. Found in the 

 clay of bituminous slate accompanying the lyas. 



The lime being removed by the muriatic acid, a con- 

 siderable volume of dark brown powder remains, which, 

 when dried, is remarkably combustible, burning with a 

 flame resembling that of some of the pyrophori. On the 

 brown spar being subjected to the action of diluted muriatic 

 acid, the bituminous matter with which it is coloured rises 

 in a film to the surface of the solution. 



The polished surface of both these fossils being examined 

 with a lens, the spathose substance is seen to have per- 

 meated the minutest woody fibres in all their directions. 

 The powder deposited during the solution of both these 

 fossils is undoubtedly the woody fibre reduced to this state 

 of minute division, in consequence of its penetration in 

 every direction by the spathose crystallization. 



II. Siliceous Vegetable Fossils. — The mineral- 

 ization of vegetable substances is most frequently effected 

 by those impregnations in which silex is the principal con- 

 stituent ; and the fossils thus formed are remarkable for 

 the correctness with which their forms and markings have 

 been preserved. 



I. Siliceous wood. — Its colour is generally greyish and 

 yellowish white, thence passing into ash grey, greyish black, 

 and different shades of brown. Its internal lustre is glis- 

 tening, its fracture more or less perfect conchoidal, showing 

 the ligneous texture. The fragments sharp-edged and 

 translucent. It is harder than opal, and easily frangible. 



