SUBSTITUTION OF SILICA. 345 



are marked with the perforations of marine worms, 

 indicating that they had floated for some time in the 

 ocean. It should, however, be remembered, that these 

 are not the first indications of vegetable life, leaves 

 have been found in the new red sandstone; and the 

 flora of the coal formation must not be forgotten. The 

 manner in which silica has deposited itself on organic 

 bodies such as the sponges is curious ; the whole of 

 the organized tissue being often removed, and flint 

 having taken its place. Flints formed by such a process 

 as this abound in the upper chalk. The association of 

 carbon and silicon, combined with oxygen, as we find 

 them in the cretaceous formations, is most interesting, 

 and naturally gives rise to some, speculation on the 

 relation of these two elements. Both carbon and 

 silicon, as has been already shown, exist in several 

 allotropic conditions ; and, although the statements 

 made by Dr. Brown relative to the conversion of carbon 

 into silicon are proved to be grounded on experimental 

 error, it is not improbable that a very intimate relation 

 may exist between these elements.* The probability is, 

 that the sponge animal has the power of secreting silica 

 to give strength to its form. "Many species/' says 

 Rymer Jones, speaking of recent sponges, " exhibiting 

 the same porous structure, have none of the elasticity of 

 the officinal sponge a circumstance which is due to the 

 difference observable in the composition of their 

 skeletons or ramified frame-work. In such the living 

 crust forms within its substance not only tenacious 

 bands of animal matter, but great quantities of crystal- 



* Experimental Researches on the production of Silicon from 

 Paracyanogen : by Samuel Brown, M.D. ; Transactions of the 

 iloyal Society of Edinburgh, vol. xv. p. 229. Experiments on the 

 alleged conversion of Carbon into Silicon : by R. H. Brett, Ph.D., 

 and J. Denham Smith, Esq. ; Philosophical Magazine, vol. xix. 

 p. 295, New Series. See also Dr. Brown's reply to the above, 

 ibid, p. 388. 



