M, Keilhau''s Theory of Granite, and oilier Rocks. 91 



chemical principles was carried as far as possible, but for the 

 rest, geological necessity was allowed to reflect back arguments 

 for the justice of the assumption on what remained as a chemi- 

 cal postulate. So long as the opinion was entertained that gra- 

 nite, in its geognostical relations, coincided with the rocks de- 

 posited from water, it was natural to suppose that it also was 

 derived from a Neptunian fluid. Granite is an aggregate of 

 crystalline minerals. The formation of crystals, on the expul- 

 sion of fluid matter existing in the form of water which held 

 them in solution, is the most common way in which we see these 

 derived, not only morphologically, but often also substantially 

 as newly formed bodies which we call crystals. The circum- 

 stance in which we here went beyond chemistry, was the as- 

 sumption, on these grounds, of the formation of felspar, quartz, 

 and mica, in^the moist way. 



In the same way has it fared with the now prevailing theory. 

 As soon as it was discovered, in consequence of our being bet- 

 ter informed with regard to the geognostical relations of un- 

 stratified rocks, that these relations could not be brought to 

 harmonize with their Neptunian origin, the Neptunian hypothe- 

 sis was cast aside, and replaced by a new one, — one known for 

 a long time previously, but that is of no consequence for our 

 argument: crystals are also produced from melted masses; 

 and although crystallization is much more frequently observed 

 to take place in the humid way, yet, in that group of minerals 

 which compose the massive siliceous rocks, according to cer- 

 tain facts regarding many of them, it could more especially 

 take place when their materials existed in a melted condition, 

 and from that passed to a compact state. With regard to 

 granite, chemistry has actually advanced so far as to be able to 

 produce, in the dry way, felspar and mica; and, so far as one may 

 wish that the chemical postulate of the pyrogenetic theory may 

 pass over entirely to chemistry, it is only wanting that we should 

 be able by fusion to procure quartz, and to produce all the three 

 minerals in combination. But to us it would be a matter of 

 little consequence the success which might attend such attempts. 



The pyrogenetic hypothesis does not satisfy the demands which 

 a mass of geognostical facts have on a theory of the rocks in ques- 

 tion, and the inquirer must look about him for a new hypothe- 

 sis. So far as is practicable, chemical experiments must be at- 



