Mr. E. J. Que RETT on some Fossil PToods. 151 



example of casts of woody tissue, with numerous spirals traversing the inte- 

 rior. At various points were arranged the ordinary coniferous dots, and to 

 the outside there adhered small bodies of the same size, which projected 

 beyond the outline of the fibre when seen obliquely, each bearing the precise 

 representation of the coniferous disc. In other parts of the field of view were 

 some of the same bodies detached from the sides of the fibres, which left no 

 doubt that they were casts of the cavities existing in the original plant, and 

 proved the correctness of the view above stated respecting the nature of these 

 minute circular markings. Besides these siliceous bodies in the fragments of 

 the fossil, there were others of such a shape as to leave no doubt that they 

 were casts of the interspaces between the cells or woody fibres. 



There is very little doubt now, from the use of chemical tests, that fossil 

 vvoods for the most part, or perhaps in all cases, still possess portions of the 

 vegetable tissues, which are cemented together into a compact mass by silica, 

 derived from the water to which the specimen had been subjected. It is difficult 

 to account for the lodgement of silica in the tissues of plants ; but it is possible 

 that the molecules of silica, which exist as one of their organic constituents, 

 form the first attractive points, to which others are added by the water, until 

 the whole of the portion of the plant, the woody fibres, the vessels and cells, 

 and the interspaces between these organs, is filled, (in fact all places which 

 in the recent plant are filled with sap and air,) after the manner that the spi- 

 cules of silica in a sponge form nuclei for the subsequent deposits of flinty 

 matter, until the whole is converted into a shapeless mass like the original 

 sponge. 



It follows from these observations, as every fibre, cell and spiral vessel is a 

 closed sac or tube, that when any vegetable tissue becomes fossilized, the 

 silica occupying their interior and their interspaces is, in fact, in detached 

 pieces, each being separated from the adjoining cell or vessel by the inter- 

 vening walls of the tissue. If fossilization went no further, and there is rea- 

 son to believe that in some cases it does not, the mass could easily be broken 

 down by slight force, and each original fibre detached from its neighbour on 

 account of the vegetable matter, after long maceration in the silicifying fluid, 

 being almost decomposed. But frequently the process goes further; and as 

 we know how readily vegetable membrane transmits liquids through its sub- 



