Mr. E. J. Quexerr on some Fossil Woods. 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 
woods 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 tached 
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 "A nogahon on 
account of the vegetable matter, after long maceration in the silicifying fluid, 
being almost decomposed. But frequently the process pe further ; and aig 
we know how readily vegetable membrane transmits liquids through its sub- 
