ON MINERAL VEINS. 393 



where, that the mutual impression of quartz, chalce- 

 dony, and calcareous spar, occurs in these, from suc- 

 cessive infiltration and crystallization ; and, according 

 to the order in which these substances are deposited, 

 either may impress the other. Thus might any 

 number of minerals, admitted at distinct intervals into 

 cavities, present the same appearances ; and even in 

 modes much more complicated than from any simul- 

 taneous crystallization in an uniform fluid of fusion. 

 And, in reality, though the inconceivable chemical 

 agencies required to separate all the minerals of a 

 compound rock from solution in water, have been 

 made almost a subject of ridicule against the sup- 

 porters of aqueous theories of rocks, that is much 

 better deserved by those who would crystallize all the 

 variety of earthy and metallic minerals found together 

 in veins, from an uniform fluid of fusion, as the che- 

 mist who is acquainted with a mineral vein well knows. 

 It is hard that even the chemistry of Geology, where 

 the better portion of Geology is Chemistry, should 

 have been settled by those who knew nothing of 

 that science. But such has been the fate of this 

 unlucky branch of Natural history, in every thing. 



Some further arguments, as much mechanical as 

 chemical, have also been adduced in favour of the 

 igneous hypothesis. It has been said, as an argument 

 from dilemma., that on the aqueous theory, no close 

 veins, or deposits of minerals surrounded on all sides 

 by rock, could exist. But it is obvious that these are 

 equally impossible on the other view of a cause. 

 Where there is no access for a watery solution 

 there is none for an igneous fluid. The inventors of 

 "igneous secretion," applied here, as to the nodules of 

 trap, ought really to explain a new process in che- 

 mistry; they have been fortunate that their opponents 



