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 Eue, who succeeded in obtaining minute crys- 

 tals of quartz by an aqueous method. De la Rue found that 

 the gaseous body, fluoride of silicon (Si F 3 ), 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 + 2SiF 3 ) produced : thus, 3 (SiF 3 + 3 (HO) = Si0 3 

 (which deposits) + 3HF + 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 ; 

 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. 2 d 



