l64 NEW YORK STATE MUSEUM 



shows a replacing network of pyrite (figure 29). Graphite is less 

 abundant than in the preceding sections. By itself this rock is too 

 much changed to show its origin, but comparison with others point 

 to its probable derivation from a pegmatite or from a gneiss of the 

 pyrite formation. The former origin is probable for a very coarse, 

 quartzose ore from the dump with large masses of quartz probably 

 of vein origin. The thin section shows a much altered quartz- 

 feldspar-mica aggregate, with abundant fibrous yellowish chlorite 

 and pyrite, a little graphite and garnet. Here the pyrite has often 

 included small flakes of mica which, more or less altered, retain 

 their outline very sharply. Graphite is not abundant. 



A section of lean ore from the lower end of the gorge shows a 

 quartzose gneiss with scattered grains of pyrite and the usual 

 accompaniment of light green chloritic material. In this section there 

 is little evidence of secondary introduction of pyrite and, standing 

 by itself without reference to other examples, the pyrite would be 

 regarded as, and probably is, a simple product of recrystallization 

 during metamorphism. But instances of this kind are so uncommon 

 as to make the prevalent relations of pyrite in the rocks more con- 

 spicuous. 



It is clear from the above that microscopic study of the ores of 

 this locality confirms the conclusion derived from field work that 

 the pyrite can not be regarded as a product of differentiation in the 

 gabbro magma. Between the two formations there is no close 

 mineralogical relationship, while the ores agree in all essential 

 respects with those of the other localities where gabbro is absent. 



GENESIS OF THE DEPOSITS 



From the foregoing brief statement as to field relations and 

 microscopic character of the ore deposits, it is evident that the avail- 

 able data are inadequate to afford the basis of any complete explana- 

 tion of their genesis. The many vicissitudes to which the pyrite- 

 bearing formation has been subjected have lead to the obliteration 

 of much evidence necessary to work out the successive steps in the 

 process of pyrite concentration. Like the closely related '' Fahl- 

 bands " and " Kieslager "of Europe, these ores belong to a complex 

 class of deposits whose origin has always been a matter of doubt. 



In dealing with such involved phenomena it is by no means easy to 

 discriminate between the essential and the incidental, and yet there 

 are certain features, common to all the pyrite occurrences studied, 

 from which some certain definite conclusions and more or less prob- , 

 able inferences may be drawn as to the origin of the deposits. 



Of these features perhaps the first that should be mentioned is 



