26 THE JOURNAL OF GEOLOGY. 
red, § dark red-brown, @ light yellow-green. In this case it 
must be noted that some of the hornblendes are of that dark red 
color which, as Belowsky* has shown, is produced by heating the 
green variety. The occurrence of green hornblende in the 
andesites is rather unusual, the color being generally brown. As 
is well known the green color is characteristic of the propylites, 
but the present rocks show none of the well marked features of 
this group, and are in every other way typical hornblende-andes- 
ites. The extinction angle is 11° 
The hornblende is in every case, oueet that mentioned 
above, perfectly fresh and unaltered, the dusty edges of some of 
the crystals, which look at first sight like incipient alteration, 
being seen on closer examination to be due to overlapping layers 
of the dust-laden groundmass. Zonal structure is occasionally 
seen, some of the crystals having the commonly observed darker 
green core. Inclusions are not common and small, though of 
considerable variety ; small crystals of biotite, augite, plagioclase 
and magnetite, with an occasional zircon or spot of brown glass, 
having been noted. The distinction between the phenocrystic 
and the groundmass hornblende is hard to draw as they grade 
into.each other with no difference of habit. 
‘ Augite is not abundant in these rocks, though occurring here 
and there in small crystals, clear and almost colorless. Inter- 
growths of this with the hornblende are not unusual, in one case 
the augite occupying the center and the hornblende forming the 
outer part of the mixed crystal; while in other cases one end is 
augite and the other end hornblende. A very few sections of 
biotite were seen in the slides; they are greenish gray, quite 
fresh, and carry inclusions of plagioclase and magnetite. 
Magnetite is quite abundant in the form of fine grains in the 
groundmass as well as larger crystals up to 2mm. in diameter. 
These last not infrequently show inclusions of plagioclase, apatite 
and zircon, and even, as in one case, have grown around the 
present groundmass. Many of these larger crystals show a 
coppery brown luster by reflected light, and, on the edges and 
*BELOWSKY. Op. cit., p. 37. 
