1 68 NEW YORK STATE MUSEUM 



Finally, of the intimate features of the deposits, the most import- 

 ant is the relation which the pyrite bears to the other minerals 

 present. So much has already been said upon this point that a brief 

 summary will suffice here. While often occurring in rounded or 

 irregular grains, whose relations to the other minerals are susceptible 

 of various, interpretations, the pyrite also frequently appears in 

 shreds, strings and veinlets cutting the other minerals in such a way 

 as to make evident that it is actually replacing them. There is a 

 strong tendency for pyrite to develop its own crystal form quite 

 independently of the surrounding minerals, and from cases of this 

 kind there is every gradation up to large bunches of pyrite replacing 

 the country rock. Such bunches occur scattered through the rock, 

 united by strings and veinlets of pyrite, and as they increase in size 

 and numbers gradually convert the rock into an ore. Associated 

 with this replacement there is often the great development of chlorite 

 referred to above, so that the ore becomes, as at Stella, a granular 

 aggregate of pyrite and chlorite, the other minerals still present, 

 with the exception of graphite, being pretty well masked by these 

 two. 



The time relation between pyrite and chlorite is not simple. As 

 previously stated, pyrite often seems to crystallize more readily in 

 contact with chlorite than with other minerals, suggesting that the 

 chlorite was present first ; but on the other hand chlorite sometimes 

 fills cracks in pyrite and is therefore younger. However, this is a 

 subsidiary phenomenon since the same chlorite fills cracks in an older 

 chlorite, so that these cases prove nothing beyond the mobility of the 

 mineral. The evidence as a whole indicates that, while closely 

 related in time and origin, the pyrite is generally somewhat younger 

 than the chlorite. Much less frequent, but not to be overlooked, is 

 the development of sericite so related to chlorite and pyrite as to 

 show that it is younger than these minerals. 



To formulate a hypothesis that will unite and explain these 

 various phenomena and at the same time harmonize with what is 

 known to be true or probable in regard to the geology of the 

 region, is by no means easy. Unquestionably the series of opera- 

 tions by which the ore deposits have been formed was exceedingly 

 complex, the available data are meager, and the best that can be 

 hoped is to get some clue to the more important agents involved. 



Assuming the rusty gneisses to be of sedimentary origin, repre- 

 senting shales and impure sandstones deposited in the Grenville 

 sea, a simple explanation of the pyrite is to regard it as a primary 



