Formation of Hyalite by the Action of Aimnonia. 51 



In this solution of silica, held in solution by ammonia, 

 which we may obtain from almost any, if not all, of our 

 springs or subterranean waters, we have^ no doubt, one of 

 the active agents of metamorphic action. Just above the 

 surface of the liquid on the sides of the vessel I find a botry- 

 oidal coating of hydrous silica, in all respects identical with 

 the mineral hyalite. 



In this artificial hyalite the-re are some infusorial forms 

 which have been entrapped. Most of them seem to be 

 partly dissolved ; some are mere skeletons of the original 

 form. 



In the mineral hyalite from our basaltic formations my 

 assistant, Mr. Dunn, finds distinct traces of ammonia, and 

 as we know ammonia is present in all our subterranean 

 waters, we have a means of accounting for these films or 

 crusts of botryoidal silica, and probably for the veins and 

 masses of chalcedony and opal found in the decomposed 

 volcanic rocks. 



A curious change has taken place in the residue of the 

 infusorial earth from which the solution was made. All 

 the forms of diatoms have vanished, and instead I find a 

 fine granular powder. The mass has shrunk considerably, 

 and is covered by a friable film. 



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