386 The American Geologist. june, isgs 
this feldspar, as here given, shows that it belongs to the anor- 
thoclase series. It is to be noticed that the silica percentage 
SiOj AI2O3 FejOg CaO MgO KjO NajO H^O Total 
67.99 19.27 0.82 0.75 0.02 3.05 6.23 0.90 99.03 
is larger than is required hy the amount of soda, potash and lime 
present; this is probably due to the fact that a small amount of 
quartz was so intimateh' intergrown with the feldspar that the 
two could not be completely separated. This feldspar is then an 
anorthoclase with approximately the composition Or^ Ab^^ An^. 
The specific gravity of several of the phenocrysts of the porphy- 
ritic facies of the rock was determined. It ranges from 2. 59 to 
2.60, which, together with analysis of the whole rock (II above), 
is sufficient proof of its being anorthoclase. 
The quartz is found .in comparatively small quantities, rarely 
amounting to more than one-quarter of the mass of the rock. 
It never occurs as phenocrysts in the porphyritic facies of the 
granite and in the granitic facies it was the last mineral to crj's- 
tallize, occupying small areas between the feldspars, which are of 
larger sizes and frequently partiall}' idiomoi-phic. 
The augite is the most interesting mineral in the rock, as true 
granites in which this mineral is the chief ferromagnesian con- 
stituent are comparative!}' rare. It makes up from five to twenty 
per cent, of the whole rock and in the majority of sections is the 
only ferromagnesian mineral present. A few small flakes of 
biotite are found in some sections, and original hornblende occurs 
less frequently. In the porphyritic facies and in the freshest 
specimens of the granitic f.acies the augite is seen in its best 
development. It occurs in short, stout prisms bounded by the 
unit prism, ortho-pinacoid and clino-pinacoid; the terminal faces, 
with the exception of the basal plane, are not well developed, 
there being a tendency' to the rounding olf of the edges of the 
basal plane, but a clino-dome is sometimes noticeable. The 
color of the augite is green, although there are parts of some 
crystals which are colorless, and entirelj' colorless individuals are 
rarely seen. A slight pleochroism is to be noticed in some sec- 
tions, a and b being green and hardly distinguishable from each 
other, while c is a yellowish green. Zonal structure is rather 
common; in such cases the center is colorless or of lighter color 
than the outer laA^ers. The colorless centers sometimes pass 
gradually into the colored rims, but usually the two are separated 
