PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 417 



Quartzyte.] 



ally as follows: (1) The oldest of these is the conglomerate and quartzyte (or 

 sandstone) represented by Nos. 254, 256, 546, 548, 549, 1831, 1832 and 1833. It is 

 stratigraphically the lowest rock on the island and occurs only on its north or north- 

 east side. (2) Overlying the conglomerate and quartzyte are certain igneous rocks 

 which are in part, and probably in whole, surface flows. These are later than the 

 underlying elastics, although it is possible that the lower part of these flows is 

 interbedded with the elastics and thus cotemporary with them. These igneous 

 rocks are represented by.Nos. 255, 543, 544, 545, 547, 1834 and 1834A. (3) A later 

 series of diabase dikes cutting both of the foregoing. These dikes are represented 

 by Nos. 541, 542, 550 and 551. u. s. G. 



No. 552. QUARTZYTE. (Plumbaginous.} 



Pigeon point, near the trail to Parkerville; sec. 32, T. 64-7 (see No. 270). 



Ref. Annual Report, ix, page 65; Annual Report, x, pages 48, 58; Bulletin vi, pages 123, 420. 



Mi'!/. Quartz plainly constitutes the greater portion of this rock, but it is 

 obscured by the colored elements. The graphite forms a metallic unctuous coating. 

 The general aspect is black. 



Mir. The quartz is secondary, separated areas extinguish simultaneously and 

 the forms are angular. 



Feldspar crystals are generally not observable, but in one case a striated feldspar 

 of the first consolidation is well preserved, and some of the microliths can also be 

 identified. 



S/i/H'i/e can be seen in numerous isolated highly polarizing gi-ains and rods of 

 irregular shape and strongly roughened surface on lowering the condenser. In 

 reflected light it is opaque white. 



Calcite also is not uncommon, the little roughness of the surface, visible on 

 lowering the condenser, being sufficient to produce a minutely speckled polarization, 

 the colors, even in a thin section (.02 millimeter), being red, blue, yellow, etc. 



One or two grains of zircon are distinguishable by reason of bright green polar- 

 ization in a very thin section, and rectangular outlines. 



Several rods also highly doubly refracting and refractive, are probably rutile. 



Pennine and biotite are abundant, and closely associated, the former showing its 

 characteristic halos, and the latter varying to a translucent mica which polarizes in 

 colors. 



(Inqtliife blackens the rock and the section, sharing this in a small degree, 

 however, with pyrite and perhaps with magnetite. Two sections. 



Age. Animikie(?) 



Remark. This rock apparently is changed from the basic eruptives of the 

 region by contact on the sedimentary rocks adjacent. 



88 



