REPORT OF THE DIRECTOR AND STATE GEOLOGIST 1900 r89 



ism, readjusting itself more by stretching and less by breakage 

 and reerystallization than that mineral. In the somewhat less 

 well foliated varieties of the rock the quartz is neither so flattened 

 nor so wholly separate from the feldspar. Neither is the feld- 

 spar so finely granular; it may be that the reerystallization of the 

 feldspar preceded the final stretching and granulation. 



Hornblende and biotite are the two dark silicates, and the 

 former is much the more important. In fact, the biotite is much 

 more properly regarded as an accessory than as an essential 

 mineral. Together they constitute from 10^^ to 15fo of the rock. 

 They are stretched out together along the cleavage planes, not 

 appearing elsewhere in the more foliated varieties, but like the 

 quartz less well alined in those less gneissoid. Both are perfectly 

 ordinary representatives of the two minerals and call for no 

 comment. 



The more acid phases of the rock here (no. 4) have only about 

 half the usual amount of hornblende and biotite, and a larger 

 quartz percentage. The feldspar augen are red instead of dark 

 colored, though consisting of the same minute fibered micro- 

 perthite. They are few in number and of small size, and are 

 always partly and often wholly granulated. Considerable micro- 

 cline appears in the mosaic feldspar. The quartz is as before, 

 and the rock practically consists of these thin, parallel quartz 

 leaves with intervening fine feldspar mosaic. In the absence of 

 an analysis, it is impossible to say just what the acidity of the 

 rock is, but, since the ordinary rock shows 66^ of silica, this 

 would appear to have at least 70fc and to be properly classed as a 

 granite. 



The two augen gneisses previously described are like the last 

 in having red feldspar augen. In no. 8, in which the augen are 

 completely granulated, microcline is more abundant than else- 

 where, though as usual anorthoclase is the prevailing feldspar, 

 the larger grains showing a faint microperthitic structure with 

 high powers. There is also quite a little micropegmatite and the 

 usual small amount of oligoclase. Here biotite is the prominent 

 dark silicate and is quite abundant, while hornblende much 



