348 Notices respecting New Books: — Darwin on the 



and as these hills, according to the view above given, consist of trachyte 

 softened and altered in situ, the presence of free silica in this case may be 

 added as one more instance to the list.'' 



Mr. Darwin truly observes, as above, that we are ignorant of the 

 means by which, in the silicification of wood, every atom of wood, 

 whilst in a perfect state, is removed and replaced by atoms of silica. 

 The recent discovery by Ebelmen, as noticed in our last Volume, 

 p. 397, of the production of silicic aethers, by the substitution of si- 

 lica in equivalent proportions for the water which in alcohol is united 

 to the oxide of a certain hydro-carbon, induces us to offer a sugges- 

 tion on this subject. Hydro-carbons, combinations of hydrogen and 

 carbon, in various proportions, are the results, as Liebig has shown 

 by a comprehensive induction from facts previously investigated by 

 other chemists, of eremacausis, and of other changes, which either 

 spontaneously occur or are readily induced, in natural operations, in 

 ligneous and other vegetable matter, and some of them, as the tur- 

 pentines, are the actual products of vegetable life. Now silicic aether, 

 it is found, is soluble in all proportions, in alcohol and aether, which 

 involves the fact of the practical indefinite solubility of silica in the 

 oxide and the hydrated oxide of that peculiar hydro-carbon which has 

 been called by modern chemists, ethyl. But if these products of vege- 

 table matter have this kind of loose affinity for silica, causing them 

 thus to unite with it in large proportions, from which it is again rea- 

 dily separable, is it not in the highest degree probable that other 

 (natural) products of vegetation, other hydro-carbons or their oxides, 

 may have a similar power of dissolving silica, readily to part with it 

 again ? If so, we have an indication of the line of research by which 

 we may hope to solve the problem of the silicification of wood. A 

 most interesting and extensive field for experiment and investiga- 

 tion, chemical, botanical, mineralogical and geological, is thus pre- 

 sented, and will be entered upon, we hope, by some competent in- 

 quirer. An accomplished man of science would be required to de- 

 vote himself to the task, necessarily an arduous one, but its success- 

 ful perfoi"mance would gain or even enhance the highest reputation. 



To return however to Mr. Darwin's researches. In the annexed 

 account of the formation of calcareous rocks on the coast of Ascen- 

 sion, and in that of a peculiar incrustation on certain rocks of that 

 island which immediately succeeds it, we have further examples of 

 that particular class of existing causes in geology which have opened 

 to him so fertile a field of inquiry. 



" Formation of calcareous rocks on the sea-coast. — On several of the sea- 

 beaches, there are immense accumulations of small, well-rounded particles 

 of shells and corals, of white, yellowisii and pink colours, interspersed with 

 a few volcanic particles. At the depth of a few feet, these are found ce- 

 mented together into stone, of which the softer varieties are used for build- 

 ing ; there are other varieties, both coarse and fine-grained, too hard for 

 this purpose : and I saw one mass, divided into even layers half an inch in 

 thickness, which were so compact, that when struck with a hammer they 

 rang like flint. It is believed by the inhabitants that the particles become 

 united in the course of a single year. The union is effected by calcareous 

 matter; and in the most compact varieties, each rounded particle of shell 



