PETEOGKArHY— MICA-SCHISTS AND SLATES; 479 



hornblende crystals being predominant and easily recognized, with white 

 spots or faint layers of feldspar or quartz and some pyrrhotite through it. 

 Under the microscope, beautiful crystals of hornblende were seen, varying 

 in color from pale yellowish-brown to dark-green and red. The pale crys- 

 tals, being sections across the vertical axis, show the characteristic cleavage 

 lines and a strong dichroism very finely. This hornblende, which is 

 greatly in preponderance over the other constituents, is very crystalline, 

 although the masses are irregular in outline. Next in importance is the 

 orthoclase, distinguished from the quartz by a little less transparency and 

 more fissures and cleavage lines ; it is quite abundant in crystalline grains 

 The quartz is present in grains and masses of tolerably good size, which 

 polarize in very brilliant colors. It contains cavities and microlites, and is 

 of about the same quantity as the orthoclase. Quite remarkable is the 

 comparatively large amount of plagioclase present. This occurs in large 

 crystals, with very delicate but well defined twin lamellations or banding, 

 some of the crystals being very beautiful. Some garnet crystals, as hexa- 

 gonal sections imbedded in the hornblende, were noted, as they are isotropic 

 in behavior. There is also some magnetite. The structure of the rock is 

 coarsely crystalline, and much fresher than [24], with more hornblende, 

 some plagioclase, and titanite. It is a hornblende-gneiss, and the section 

 observed in polarized light presents a beautiful appearance, owing to the 

 great variety of brilliant colors. 



The rock [64] from Rapid Creek is very dark indeed and fine-grained 

 and slaty in character, so that it can be cleaved into flat, tolerably smooth 

 pieces. Thin veins of white quartz traverse it at right angles to the strati- 

 fication, and are occasionally of considerable thickness. In the section, it 

 was observed that the rock consists largely of quartz in rounded grains, 

 large and small, and dark colored nearly opaque mica, and has a distinct 

 schistose structure. Sometimes a large mass of mica is seen, but most of 

 it is in very small particles, fibrous in character. The veins of quartz are of 

 course conspicuous, polarizing as well as the grains with bright colors. A 

 little triclinic feldspar and one small hornblende crystal were noted in the 

 slide. 



The fibrous character of the groundmass, so plainly of a schistose 



