PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 799 



Quartzy te and black slate. Red granite.] 



NO. 1852. QUARTZYTE AND BLACK SLATE. 



Governor's island, at the mine (or shaft) of the Pigeon Point Silver and Copper Mining company; south 

 side of the island. 



Ref. Annual Report, xxii, page 10. 



Meg. Quartzyte and slate in sedimentary succession. It is apparent that while 

 the shaft started in hardened slate at the surface, the excavation struck red quartzyte 

 and finally red granite. 



Mic. The quartzyte is wholly recast into an interlocking, almost granitic, 

 reddish rock, largely composed of quartz, but holding, in the interstices between the 

 grains, occasionally a dirty feldspathic element, which probably is accountable for 

 the reddish color of the rock. This element composes in some places nearly one- 

 quarter of the rock, and it is interlocked with the secondary quartz grains. It is so 

 crowded with fine inclusions that it cannot be determined specifically. Its extinctions 

 are vague and not to be measured. Its inclusions are hematite, fine and dust-like, 

 actinolite, tourmaline and a highly refractive, glassy-transparent mineral in isolated 

 occasional grains resembling sphene in all respects, so far as determinable, except in 

 having a double refraction much lower than that of sphene. One of the larger 

 grains, giving an axis of elasticity perpendicular, thus showing the direction of the 

 axial plane, indicates epidote. Still other scattered grains are undoubtedly sphene. 

 These characters appertain to the quartzyte portion of the rock. 



The " black slate " portion is colored by very fine biotite, but also contains 

 sericite. These lie in a very fine background of micro-granulitic feldspar which is 

 only occasionally discernible by reason of the great number of the little biotites. 

 With the biotites are seen occasionally tourmalines almost equally small, distinguished 

 easily between crossed nicols by their lower birefringence, and with the upper nicol 

 removed by their greater absorption in a direction the opposite of that of the biotites. 

 Two sections. 



Age. Animikie. 



Remark. This rock is wholly recrystallized, the sandstone is a quartzyte 

 granitized, and the black slate is a mica schist. N. H. w. 



No. 1853. RED GRANITE. 



Prom the bottom of the shaft, same place as No. 1852. 

 Ref. Annual Report, xxii, page 10. 



Mey. Red granite, medium grained. 



Mic. This rock is like the quartzitic portion of the last, except in being more 

 coarsely crystalline, and hence more easily examined. The feldspar is prevailingly 

 of orthoclase, and zoned, but some of it shows both albite and pericline twinning. 

 The central portions of the larger crystals are frequently more affected by alteration 



