174 . NEW YORK STATE MUSEUM 



ville took place in part under such conditions of load that the lime- 

 stones and the gneisses behaved very differently, the former flowing 

 like putty, while the latter were often greatly fractured. Doubtless 

 this fracturing came at a time subsequent to the general metamorph- 

 ism of the rocks, with decreased cover ; and as it is under these con- 

 ditions that the ore deposits are thought to have formed, it follows 

 that the active solutions would have found much readier channels 

 of circulation in the fractured gneisses than in the soft and putty- 

 like limestones. This is regarded as an important, if not the chief, 

 cause of tlie localization of ore deposits in the gneisses. 



That the tw^o types of rocks in question actually did afford such 

 different conditions affecting circulation is clearly indicated by their 

 relations to intrusions of the magma itself, and particularly such 

 portions of the latter as are most closely related to magmatic solu- 

 tions. On the one hand, as before stated, the gneisses and schists 

 are repeatedly converted into injection gneisses, soaked through and 

 through b}^ granitic material often with highly developed lit-par- 

 lit structure. Such injected material is often very acid, and peg- 

 matitic on a small scale, and the sheets may be exceedingly thin. 

 In other cases the gneiss is reduced to tiny fragments entirely sur- 

 rounded by injected material. All the phenomena point to a very 

 high degree of fluidity in the injected magma, approaching closely 

 to the mechanical condition of the pyrite-forming solutions. In 

 the limestones, on the other hand, such injection phenomena are 

 rare, if they ever occur, all intrusions being comparatively massive 

 in character. The contrast is striking and points clearly to the 

 difference in the two types of rocks, as regards their reaction to 

 pressure, as its cause. That the same eft'ect would be produced 

 upon the somewhat later circulation of magmatic waters forming 

 the pyrite, is a natural and justifiable conclusion. 



The possible function of graphite in the concentration of pyrite 

 is a most obscure problem and its adequate treatment would greatly 

 transcend the limits of this paper, involving as it does two distinct 

 questions — the origin of the graphite, and its power to precipitate 

 pyrite under the conditions present. As to the former question, in 

 rocks of such antiquity affected by profound metamorphism and in- 

 tense igneous activity, the writer would be more inclined to judge of 

 the origin of the graphite from the nature of the rock containing it, 

 than to regard the rock as sedimentary because it carries graphite 

 of supposed organic origin. In the present instance, the pyritiferous 

 formation as a whole is for many reasons regarded as sedimentary 



