178 NEW YORK STATE MUSEUM 



The gabbro, though extensively developed in the region immediately 

 surrounding Pyrites, and extending well over toward, if not to Stella, 

 is not a common rock elsewhere in the region, and so far as known 

 does not occur anywhere in the vicinity of the other pyrite deposits. 

 If, therefore, the present knowledge of the areal geology of the 

 region may be trusted, it seems necessary to conclude that the gab- 

 bro is quantitatively insufficient to explain the origin of the pyrite 

 as a whole though perhaps of importance in the two localities named. 

 On the other hand, granites, both massive and gneissoid, with peg- 

 matitic and -other modifications, are everywhere abundant, and if 

 magmatic agencies pla}^ the role that has been assigned to them 

 there can be no doubt that their source must be sought in the 

 granitic reservoirs. 



Not only is this conclusion demanded by the general distribution 

 of the igneous rocks, but it is strongly indicated by the actual occur- 

 rence of pegmatites in all the ore deposits and also by the abundance 

 of vein quartz similar to that often associated with the granite and 

 pegmatites of the region. It is then in the granite magma that a 

 source is found for the heated solutions rich in HoS and doubtless 

 containing other chemical reagents, and iron, and it is to the circu- 

 lation of these solutions in the gneisses and schists that the concen- 

 tration of the ore bodies as they now occur is ascribed. As before 

 stated, however, deeply circulating meteoric waters would probably 

 be capable of prodiicing the phenomena observed. Igneous agencies 

 are invoked on the general ground of their high efficiency and on 

 the special ground of their abundance in the region as a whole and 

 the constant presence of their products in association with the ore 

 deposits. 



The conditions under which the deposition of pyrite took place are 

 regarded as, in essence, similar to those prevailing in the formation 

 of fissure veins, in so far as these latter are replacements of the wall 

 rock. In this connection much interest attaches to the following 

 quotations from Lindgren's exceedingly valuable paper on '' Metaso- 

 matic Processes in Fissure Veins."^ " Of all the sulfids occuring 

 as metasomatic minerals, pyrite is naturally the most common. The 

 mineral has a remarkable tendency to crystallization when develop- 

 ing in the rock, as contrasted with its often massive texture when 

 occurring as a filing of open spaces. The forms assumed are either 

 cubes or pentagonal dodecahedrons, or a combination of both. Pyrite 

 develops in nearly every one of the ordinary constituents of rocks. By 



1 Lindgren, W. Trans. Am. Inst. Min. Eng. 30, 1900, p. 578-692. 



