PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 735 



Unmitc. Gneiss.] 



Meg. The hand samples show two kinds of granite welded together in a distinct 

 contact. One is quite coarse grained and the other is very much finer grained. The 

 section was made from the coarser granite. 



Mir. The rock is characterized by much quartz in large grains interlocking in 

 the manner of the granitic and granulitic quartzes of Kekequabic lake. The feldspars 

 are orthoclase, oligoclase and microctine. The former two are partly fresh and partly 

 much altered, the altered portions being as a rule at the centres of the crystals. 

 The interlocking border is nearly always composed of fresh feldspar. The micro- 

 cline is wholly fresh and interlocking. Sphene and apatite are in distinct character- 

 istic crystals. Hornblende and biotite compose an inferior portion of the rock. One 

 section. 



Age. Archean granite. 



llcDKtrk. In the foregoing slide can be seen several instances of hornblende 

 entirely included within the old feldspars, having the short, stout habit of the augites 

 seen in the feldspars of the Kekequabic lake esterellyte, but in general the hornblende 

 is elongated, and is distinctly associated with the later growths. N. H. w. 



No. 1515. GRANITE. 



North Redwood P. O., near Redwood Palls ; Minnesota river. 

 Ref. Annual Report, xviii, page 59. 



Meg. Massive, gray, uniform, without bands of color, but having a gneissic 

 elongation of the crystals. 



Mic. There is much of the old feldspathic element in this rock, and though filled 

 with impurities it shows in some instances its albite twinning. The most of the 

 rock still consists of fresh </niuiz, microcline, micro pegmatyte and of sphene, with 

 some biotite and broini hornblende. One section. 



Age. Archean. N. H. w. 



No. 1516. GNEISS. 



Same place as No. 1515. 



Ref. Annual Report, xviii, page 60. 



Meg. Gray, with alternating and intershading of micaceous and feldspathic 

 belts. 



Mic. The section is made transverse to the banding, but the structure is not 

 apparent in the slide. The rock is similar to the last, except that the contrast between 

 decayed and undecayed feldspar is not so marked. There is a small amount of what 

 may be considered an old feldspar, but the whole rock appears to have suffered a second 

 incipient alteration. Even the fresh microclines are dimmed by it. Biotite and 

 sphene as in the last, with a grain of garnet. One section. 



Age. Archean. N. H. w. 



