202 ON THE ORIGIN, MATERIALS, COMPOSITION, 



in the West Indian islands at this day, or where it has 

 united fragments of discordant natures, as it does on 

 the shores of Messina and on many of our own sea 

 coasts. Thus calcareous rocks, both simple and com- 

 pound, are formed by water. Lastly, rocks of this 

 nature are now daily produced in many parts of the 

 great ocean, by the efforts of marine animals; the 

 deserted coralline structure being cemented, partly by 

 the actions of the animals themselves, and partly by 

 that of the sea on the calcareous earth, tri the same 

 manner, antient submarine piers, as at Carthage, be- 

 come cemented through lapse of time, into masses of 

 solid rock, by the intervention of shell fish and the 

 solution of their calcareous matter. In this way, 

 calcareous rocks are formed, partly by chemical 

 agency, and partly by that of submarine animals. 



Where iron becomes converted from the metallic 

 or oxydulous state to that of rust, it becomes the 

 cement of all the smaller materials within its reach ; 

 and thus sandstone is often formed on sea shores, in 

 sand and gravel beds, and, very probably, to a consi- 

 derable extent, in the noted ferruginous sand stratum 

 of England. 



Thus two modes of producing rocks by the agency 

 of water are demonstrated. It remains to inquire 

 what probability there is that the same agent can con- 

 vert silica to that end ; as we cannot produce any in- 

 stances so perfect of its absolute action in that way. 



The solubility of silica in water cannot be a matter 

 of dispute, however difficult it may be to effect its 

 solution in our laboratories. In the chapter on the 

 formation of veins, I have produced nearly all the in- 

 stances of this nature that are required for the present 

 purpose ; but I may here add to these, its actual so- 

 lution in the hot waters of Iceland and Italy, and the 



