152 NEW YORK STATE MUSEUM 



suggests that the soft chlorite is easily displaced mechanically, as well 

 as chemically, by the pyrite, a conclusion which of course implies the 

 later formation of the last named mineral. That this is true of at 

 least part of the pyrite, there can be no doubt. The section in ques- 

 tion is a cataclastic pegmatite, similar to that from which figure 13 

 is taken, and shows the same development of pyrite, beginning in 

 cracks and extending from them into the surrounding solid minerals. 



THE FARR MINE 



The Farr mine, some two miles northeast of the Styles mine, 

 resembles- the latter very closely in its geological relations. Here 

 again the ore is part of a narrow band of rusty gneiss hardly exceed- 

 ing thirty feet in thickness, with limestone above and below, while 

 again pegmatite is conspicuous. There is a large mass of the latter 

 rock, free from pyrite, some twenty feet from the shaft, while in the 

 dump there is abundant pegmatite containing much pyrite. As the 

 latter increases in quantity it passes into fairly rich ore. Judging 

 from what could be seen when the locality was visited, the pyritifer- 

 ous pegmatite is an important part of the ore. The rock contains an 

 abundance of the light brown tourmalin seen in the pegmatite of 

 the Styles mine. This mineral is conspicuous in some of the strongly 

 replaced specimens. . 



A section of the pyritiferous pegmatite shows large areas of pyrite 

 from which veinlets extend out into the surrounding quartz and 

 feldspar. Figure 14 shows an example where such veinlets traverse 

 what was originally a single individual of quartz, without the slight- 

 est disturbance in optical orientation of the now separated parts. It 

 is clear that these parts have not been moved with reference to each 

 other, but that the pyrite has replaced an equivalent amount of 

 quartz, the process starting along minute cracks. Its continuation 

 would lead to a complete replacement of quartz by pyrite, which is 

 doubtless the manner in which the larger masses of pyrite have orig- 

 inated. An even better case, perhaps, is shown in figure 15 where 

 the veinlets of pyrite traverse several individuals of quartz, with no 

 disturbance of their optical orientation and continue down through 

 several other grains, outside of the field of the microscope. The 

 only section of schist from this locality examined under the micro- 

 scope shows, in addition to the ordinary quartz, feldspar and mica, 

 sillimanite, tourmalin, garnet, some pyrite and graphite. It is evi- 

 dently a Grenville sediment, but presumably has been affected by the 

 pegmatite, as indicated by the tourmalin. 



