THE GEOLOGIST. 
81 
gation as to the manner in which minerals and rocks are formed 
and destroyed by nature. — Since the well laiown experiments of 
Sir James Hall, who transformed chalk into granular or saccharoid 
limestone in a lieated and hermetically closed gun barrel, 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, akeady 
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 paljiable than when it is brought to 
bear upon the plutonic or eruptive rocks, such as basalt, granite, 
protogine, feldspar, &c., which, from their massive structure and 
hardness, would rather seem to be completely indestructible by an 
agent apparently so hannless 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 detei-mines the 
decomposition and disaggregation of the rock. If we take, for 
instance, a piece of hard basalt, and grind it down in presence of 
water, the species of paste which is thus formed, presents, in a 
veiy 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 
ban-el is found to have dissolved a considerable quantity of 
alkaline sUicate. 
M. Becquerel in order to obtain some idea of the chemical 
actions that have taken place in the sedimentary strata, at the time 
they were covered over, uplifted, and heated by the erujitive rocks, 
such as granite, porphyry, basalt, &c., has minutely studied the 
