PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 801 



Aporhyolyte. Diabase.] 



Mic. A part of the slide is occupied by interlocking fine quartzes, or quartz and 

 feldspar, through which are disseminated a few small areas in which a multitude of 

 fine polarizing spicules are grouped altered hornblendes or feldspars. In this part 

 appear the bipyramidal quartzes of the first consolidation. This part is encroached 

 on by a spherulitic arrangement which is more stained by hematite, and in which is 

 a more evident rhyolitic structure. In this part were originally phenocrysts of feld- 

 spar (and one of sphene) and amygdaloidal cavities, evinced by the forms now left. 

 These forms are now occupied by secondary products, or are empty, owing to the 

 extreme thinness of the slide. This part is wholly rusty with iron oxide, which, 

 however, is so disposed as to reveal numerous minute skeleton crystals whose nature 

 is unknown, as they are now evident only by the peculiar but regular distribution 

 of the iron oxide in varying amounts. There are also lines of iron oxide which were 

 formed by the accumulations concentrating in cracks as the glassy substance rapidly 

 cooled. One section. 



Age. Cabotian. 



Remark. It is an interesting fact that here the " red rock " series, porphyritic 

 with quartz and feldspar, probably comparable with the rock of the "Great Palisades," 

 exhibits both porphyritic and amygdaloidal structures, showing that it flowed as a 

 lava at the surface. The source from which the red rock supply was derived was 

 hence a large one, and the clastic materials which supplied it were probably from a 

 deep source, involving formations older than the Animikie. N. H. w. 



No. 1863. DIABASE. (Basaltic? ) 



North side of Brule' lake, at the portage north to Lost lake. 

 Ref. Annual Report, xxii, pages 10, 11. 



Meg. Dark gray or reddish weathering, holding phenocrysts of feldspar. 



Mic. The groundmass in general and especially the small feldspars are reddened 

 by iron oxide, and the augite is wholly altered to hornblende, but these hornblendes 

 are long and needle-shaped, without any preservation of the ophitic structure, if such 

 ever existed. At the same time many rather large spicules of magnetite unite with the 

 feldspars and the hornblendes in giving the rock a decidedly "radiated " structure. 

 At the same time the large phenocrysts of feldspar are so altered to kaolin that they 

 are wholly unidentifiable specifically. One section. 



Age. Cabotian. N. H. w. 



No. 1864. DIABASE. (Basaltic? ) 



South shore of Brule" lake ; S. W. J sec. 13, T. &3-3 W. 

 Ref. Annual Report, xxii, page 10. 



Meg. Porphyritic. 



Mic, This rock is quite like the last, but the magnetite needles are arranged 

 rather uniformly in one direction, as if due to a prevalent original structure. This 



52 



