PETKOGRAPHIC GEOLOGY AND DESCRIPTIONS. 677 



Flint. Feldspar schist.] 



Meg. " Composed of pieces and granules of a dark-gray, aphanitic rock, varying 

 in size from that of a pinhead to peas or larger, closely compacted together; * * * 

 the general aspect being that of a dark, basic, dense diabase, specked with minute 

 white spots." 



Mir. Consists essentially of excessively fine, interlocking grains of quartz, as 

 in the last, with a slightly schistose distribution of a scant, dirty, green substance, 

 which gives opacity to the rock, as well as a slightly gray color. Occasionally this 

 green substance shows a sprinkling of aHinofife fibres, and in other places it is stained 

 by fu'n/dfiti'. One section. 



Age. Animikie. 



Remark. Another section shows a non-schistose, even distribution of the finely 

 globular green substance, with areas of calcite. This rock is apparently produced by 

 a finer association of the elements found in No. 1276. N. H. w. 



No. 1278. FELDSPAR SCHIST. 



Mouth of the creek, east end of the long bay, north side of Gunflint lake (Canada). 

 Ref. Annual Report, xvi, pages 67, 119; Annual Report, xvii, pages 199, 202. 



Meg. Schist, light green, fine grained, with pyrite. 



Mic. The rock consists essentially of very fine angular grains of feldspar, lying 

 in an abundant mesh of the well-known translucent, but nearly isotropic, chloritic 

 substance, which results from alteration of ferro-magnesian minerals, whether in 

 the massive rocks or in their detritus. This mesh has a prevalent elongation and 

 structure in one direction. It has a few fibres that polarize distinctly, which may be 

 of (ictinoUtc or n/covite, and much calcite, the latter being not infrequently aggre- 

 gated in masses of considerable (microscopic) size. 



The feldspar grains are in two conditions whether two species it is impossible 

 from this slide to determine. One sort is clear and fresh, though not glassy, giving 

 the low gray colors of the first order in a section of the normal thinness, without 

 visible impurities. The other sort is so crowded with minute grains and crystalliths 

 that they are nearly as dark between the rotating nicols as the chloritic mesh. It is 

 possible to explain this difference by assuming that the clouded feldspars are original 

 fragmental grains lying still in the detritus in which they were deposited, and that 

 the fresh feldspars are of secondary growth in situ under the action of metamorphic 

 forces. As to shapes and sizes, these grains do not differ notably, and they are both 

 slightly elongated, prevailingly with the schistosity. They all have a shadowy 

 extinction, and this is noticeable in the fresh grains, because in the clouded grains 

 the indefiniteness of extinction prevents observation on this point. As to relations 

 of orientation, they do not seem to have any dependence, one on the other, as might 

 be expected if the fresh grains were secondary developments in the vicinity of older 



