140 GEOLOGICAL SURVEY OF THE TEREITOEIES. 



and more gueissic aud grauitic beds come in until they wholly predom- 

 inate. 



At a point farther north, near the Little Thompson, a few exposures 

 of similar quartzites show them to be associated with a highly quartz- 

 iferous series of greenish color, and apparently impregnated with acti- 

 nolite, which occurs in small radiated jjatches. Bedded directly in the 

 mass are many small granitic and gneissic strata. Longitadinally the 

 beds pass into dark, finely-laminated mica schists, but beyond are lost be- 

 neath the unconformable and comparatively little disturbed Triassic 

 shales. Beneath them the grauitic gneisses occur to an enormous thick- 

 ness, with schists here and there, all apparently bedded in conformity. 

 Both these occurrences of quartzite are near the limits of the range, 

 and in the upper portion of the series exposed beneath the newer sedi- 

 mentaries. At two other points only were quartzites observed, one 

 having the radiated actinotite impregnations. Schists inclining to 

 gneisses occur over large areas, but the dominant rocks are granitic 

 gneiss, or even granites, aud of these the tendency is decidedly toward 

 a binary granite to which the name of Aplite might apply, a rock with 

 a decided predominance of the quartzose and feldspathic elements, the 

 micaceous ingredient being frequently nearly absent. The latter usually 

 occurs in small black flakes, with the feldspar in greater part orthoclase, 

 in large flat crystals, twined in two thin plates parallel with the flat 

 faces, and of white or reddish color, the mass being rather loosely tex- 

 tured and inclined to crumbling. Great areas are composed of this sim- 

 ple feldspathic granite, and while it may appear structureless for long 

 distances, yet search seldom failed to find evidences of structure, such 

 as inclosed masses of schist, perhaps several hundreds of feet in extent, 

 passing by imperceptible stages into the inclosing granite. Perhaps 

 patches only a few miles in extent, or a congerie of patches all parallel, 

 but separated by the better defined granite, may only remain to attest 

 former structure. When sufficient mica is present a gneissic structure 

 may indicate bedding, but in the ternary granites, or when the mica is in 

 too small flakes to clearly show a parallelism, the less changed and iso- 

 lated remnants of former structure must be resorted to. In a few in- 

 stances when bedding was not thus indicated by the mica the tabular 

 feldspar crystals were observed all arranged in jiarallelism with the bed- 

 ding, and in others a marked per cent, of the crystals were so arranged 

 as if the crystalizing forces had been partially controlled by the original 

 structure of the mass, just as in well-defined schist or gneiss the crys- 

 tallizing out of the mica seems to have so been determined. 



When the almost structureless granite is homogeneous over consider- 

 able areas, the characteristic " dome " form is developed in the erosion 

 and weathering of the country. The most structureless granite of all 

 was an exceedingly compact and hard i^orphyritic granite which was 

 observed but in a few small areas- aud bore an impress (^ an erupjive 

 origin. In it the feldspar crystals were not so tabular, while the rock 

 was closely built and not so loosely textured as in the broader masses 

 of the more friable granite with tabular feldspar crystals ; yet in one of 

 these masses, apparent transitions from adjacent schists could be ob- 

 served. 



That the characters noted above are evidences of a structure that 

 once existed throughout the whole mass ; that the inclosed schistose 

 patches and areas are neither remnants of foreign schists inclosed in an 

 eruptive granite mass, nor accidental lamination,developed by crystalli- 

 zation or motion in a plastic rock, is abundantly proved by the fact that 

 whenever, over a continuous area, a great many of the strikes and dips 



