THE GEOLOGIST. 



81 



gation as to the manner in which minerals and rocks are formed 

 and destroyed by nature. — Since the well known experiments of 

 Sir James Hall, who transformed chalk into granular or saccharoid 

 limestone in a heated and hennetically closed gun baiTel, many 

 philosophers have attempted to produce in their laboratories, the 

 mineral productions found in nature. These attempts have been 

 attended, in many cases, with perfect success, and the list, already 

 rather considerable, of artificially formed minerals, is daily in- 

 creasing. 



Whilst M. Daubree has been calling the attention of the Aca- 

 demy of Sciences to the rapidity and ease with which the Feldspar 

 rocks undergo decomposition by the action of water, M. Becquerel 

 has investigated the action of pressure and high temperatures in 

 the production of artificial minerals. — Every one has remarked the 

 prodigious action which water exercises upon minerals in general, 

 but, however paradoxical the assertion may appear, nowhere can 

 this action be rendered more palpable than when it is brought to 

 bear upon the plutonic or eruptive rocks, such as basalt, gi-anite, 

 protogine, feldspar, &c., which, from their massive structure and 

 hardness, would rather seem to be completely indestructible by oxi 

 agent apparently so harmless as water. But these rocks contain, 

 all of them, an alkaline silicate, soluble in water, and it is the 

 separation and dissolution of this silicate that detennines the 

 decomposition and disaggregation of the rock. If we take, for 

 instance, a piece of hard basalt, and giind it down in presence of 

 water, the species of paste which is thus formed, presents, in a 

 very short time, an alkaline reaction, rendered evident by 

 test paper. — M. Daubree has made a like experiment on a 

 larger scale. He places in a barrel full of water, to which 

 a movement of rotation is given, small fragments of quartz 

 and feldspar. In a few hours the water contained in the 

 barrel is found to have dissolved a considerable quantity of 

 alkaline silicate, 



M. Becquerel in order to obtain some idea of the chemical 

 actions that have taken place in the sedimentaiy strata, at the time 

 they were covered over, uplifted, and heated by the eruptive rocks, 

 such as granite, porphpy, basalt, &c., has minutely studied the 



