Professor Keilhau on Crystalline Silicide Slates. 161 



deration of which erroneous paths have also been followed, in 

 consequence of the prevailing, and, as it is pretended, highly 

 philosophical, but, in fact, altogether incorrect maxims. It is 

 to the crystalline silicide slates that we are now to direct 

 our attention. 



CRYSTALLINE SILICIDE SLATES. 



Regarding these formations, we see one party directly deny- 

 ing palpable facts, and proposing the most unnatural hypotheses, 

 in order to keep on good terms with chemistry, whose claim 

 to the office of judge in the matter no one has yet examined 

 with attention ; while the other party, overpowered by the 

 evidence of the phenomena as displayed in nature, certainly 

 are near seeing the truth, but still, in consequence of tradi- 

 tional scruples, stop short of its full perception, and, at the 

 same time, affect a language which sounds like homage paid 

 to the principle, — that geological results must always be che- 

 mically comprehensible. 



The hypothesis of the Wernerian school of the direct hy- 

 drogenic formation of gneiss, mica-slate, &c., meets with no 

 support either from chemistry or geology, and is now scarcely 

 adopted by any one. Some have brought forward the opin- 

 ion that these formations must be masses derived from the 

 interior of the earth,* which became what they now are from 

 a melted condition ; while others suppose that they are sedi- 

 mentary products, which have been transmuted by volcanic 

 agents. 



The idea of the crystallization of such rocks after a previous 

 condition of liquidity, is shewn to be quite absurd even by the 

 consideration of their petrographical constitution; for they are 

 slates. If such are to be regarded as produced by the solidi- 

 fication of masses which have been in a burning liquid state, 

 then that which receives no support from any one observation 

 is assumed to be possible, and thus the very rule to which 



* Leonhard includes these^formations among those which are of direct plutonic 

 derivation ; and by this he means that they ascended from the depths of the earth 

 in the form in which they now are ( ? ** als solchc," that is to say as gneiss, &c.), 

 and that they were the first solidified crust of the red-hot globe. It is not easy 

 to perceive how both these suppositions can be admitted together. 



VOL. XXXVII. NO. LXXIII. JULY 1844. L 



