£14 ON CONGLOMERATED ROCK^. 



be composed sometimes of crystallized quaftZy 

 connected together without a basis, sometimes of 

 quartz in angular or roundish concretions also join- 

 ed together without a basis. The quartz is some- 

 times intermixed with concretions or crystals of 

 felspar, and these appear imbedded in the quartz 

 in the same manner as grains and crystals of fel- 

 spar are in porphyry or granite ; and mica occurs 

 in these rocks in the same mineraiogical relations. 

 These sandstones, then, do not differ from granite 

 or porphyry in structure, and therefore are to be 

 considered, like them, as chemical formations, or as 

 having been deposited from a state of chemical so- 

 lution. Other sandstones are entirely composed of 

 quartz in granular distinct concretions, and these 

 are sometimes so pure, that they might in single 

 band-specimens be confounded with primitive 

 granular quartz. If, then, primitive granular 

 quartz be a chemical deposite, of which there 

 ear not be a doubt, certainly this sandstone must 

 also have been deposited from a state of che-- 

 mical solution. But this beautiful and highly 

 crystalline quartzy sandstone alternates in beds 

 with that variety of sandstone which resembles 

 the common building sandstone of this vicini- 

 ty ; it even occurs in the same stratum or bed 

 with it, and there is an uninterrupted transition 

 from the one into the other ; if, therefore, the 

 quartzy sandstone be a chemical deposite, the same 

 must be the case with the common building sand- 

 stone. The occurrence of a clayey or marly basis 



