On the Silicification of Organic Bodies, 
205 
process of silicification considerable ruptures of the vessels 
had taken place, and that the wood was in a recent state at 
the time of fossilisation. I may further state, that the late 
Robert Brown showed me a section of silicified wood which 
fully corroborated the reasoning of Dr Bowerbank, as it bore 
distinct evidence of having been alive, and struggling to live, 
during the process of silicification. That the solution of 
silica in the humid way was not so difficult as many geologists 
supposed, chemists' experiments all tend to prove that it is 
soluble in a large degree. I especially refer to the experi- 
ments of De la Rue, who succeeded in obtaining minute crys- 
tals of quartz by an aqueons method. De la Rue found that 
the gaseous body, fluoride of silicon (Si Fg), is decomposed 
by contact with water, one-third of the silicic acid being de- 
posited in the form of jelly and silicated hydrofluoric acid 
(3HF + 2SiF3) produced : thus, 3 (SiFg + 3 (HO) = SiO^ 
(which deposits) + 3HF -f 2SiF3 (which remains in solu- 
tion) . 
The deposited silica is extremely soluble in water, and he 
observed that the silicated-hydrofluoric acid always retains a 
portion of uncombined silicic acid in solution, which deposits 
after the lapse of some months in minute crystals of artificial 
quartz. It thus appears that water is the solvent of the silica, 
which, when recently produced or separated from its combina- 
tions by the action of the atmosphere on the earthy silicates, 
is presented in the modification most favourable for solution. 
The conclusions to be drawn from these experiments simplify 
very much our ideas of the silicification of wood shells and 
other organic bodies. Geologists hitherto have sought the 
explanation of the phenomena of petrifaction in the action of 
intense heat aided by pressure. It is clear, however, from 
the facts adduced by Dr Bowerbank, that such agencies could 
not have obtained during the silicification of his Alcyonium i 
and further, it appears from the preservation of the most 
minute tissues in fossil woods, that pressure and extreme heat 
could not have been present. 
With regard to the preservation of the minute tissues in 
various fossil woods, especially the pines and araucarians, as 
shown in their radial sections, I had always found a difficulty 
VOL. II. 2d 
