326 Formation of Minerals in the Humid Wat/. 



Daubree obtained titanic acid crystallised by the action of the vapour 

 of water upon the chloride of titanium at a high temperature ; the 

 crystals were however identical with JBrookite. 



3. Experiments upon the Formation of Minerals in the Humid 

 Way, in Metalliferous Repositories. By M. de Sanarmont. 



Geology has means of investigation which are peculiar to itself, 

 and now comprehends a certain number of especial truths definitively 

 acquired to science. 



It is thus that geology has been able, without foreign aid, to 

 characterise the manner of the formation of the sedimentary rocks, 

 and to arrange them in series ; it is thus that it has succeeded in 

 distinguishing in crystalline rocks, and in metalliferous repositories, 

 different classes of which it can assign the probable origin ; and in 

 so far as it has not drawn conclusions too far removed from its 

 fundamental principles, its anticipations have almost always been con- 

 firmed by experiment. 



It is to mineralogical chemistry that geology owes the useful ex- 

 perimental control of its I'ational conceptions. Crystalline mine- 

 rals have, in fact, a complete chemical origin ; and it is chemical 

 experiment which ought to support geology in its future progress in 

 the study of the rocks of which it is composed. 



Chemistry, then, can do much for geology by lending its means 

 of experiment ; but upon the condition of itself remaining purely 

 geological ; and of borrowing in its turn particular means of study, 

 and the general data which the science a priori has collected upon 

 all the conditional peculiarities of structure, relative position, associa- 

 tion, or mutual exclusion, to which certain mineral species must 

 needs be subject. In a word, it is necessary that all the circumstances 

 where the natural operation has left characteristic traces, discovered 

 by the geologist, should reappear in the artificial operation of the 

 chemist. 



The experiments, then, of mineralogical synthesis should embrace 

 the different groups of mineral species which are united in nature, 

 and should support themselves upon certain probable geological in- 

 ductions concerning the formation of the beds which they enclose. 

 Certain isolated species have already been obtained, and principally 

 those which approximate to the usual products, according to the dry 

 method. I have attempted to do more, and to discover some indices 

 of the general causes which have originated the different classes of 

 metalliferous beds. 



I now commence this great problem, by the study of the concre- 

 tionary veins which approach most nearly to the existing formations ; 

 'u/n;a !ifq yjg jdjiv/ h^iiimmuoi\ ,«ingi'iq bal)! 



