The Grit. 
221 
augen of quartz in the schist, the pressure giving rise to the 
lenticular form of these augen as well as giving rise to the sec¬ 
ondary mineralogical changes which have taken place. Local 
deposits of grit will account for these augen. The materials of 
the grit were of such chemical nature that ottrelite formed dur¬ 
ing the dynamic metamorphism which followed deposition. 
THE GRIT. 
The grits are made up largely of quartz grains, on the average 
£ cm. in diameter. The grits are often rich in different mineral 
ingredients. They contain not only ilmenite, magnetite, biotite 
and hornblende and more common ingredients, but also staurolite, 
garnets, zircon, and rutile. All these included minerals are 
usually surrounded by zones of graphite. In these rocks as in 
others of the series, the schistosity depends upon the mineral 
ingredients. If feldspars be abundant, especially if altered to 
to sericite or chlorite, schistosity is well developed; but in pro¬ 
portion as quartz enters into the composition of the rocks the 
schistosity disappears. Interbedded with the dark schists are 
light gray schists, resembling those already described as exist¬ 
ing near the granite area. 
In the ground mass of this rock, though there are yet unal¬ 
tered feldspars, the greater portion of this mineral has be¬ 
come sericite. The latter occurs in its characteristic felty ar¬ 
rangement, parallel to the cleavage, so perfectly are the fibres 
oriented that they all extinguish at once, except diagonal patches 
which do not so extinguish, but a further turning of the stage 
through 50°-60° is necessary before they become dark. These 
portions are therefore not oriented with the main mass, but are 
turned to one side some 60°. The disturbed portions are nar¬ 
row bands crossing the schistosity diagonally. 
These bands are dark when the rest of the slide is light. The 
microscope shows that the sericite in these bands has been forced 
out of its orientation and folded into minute ridges, each band 
constituting a ridge. These minute folds are found to agree 
with those folds which in the field were made by the second N. 
W. force. In this occurrence is found the beginning stages of a 
double schistosity. If the slight folds had suffered still further 
