288 The AmeiHcan Geologist. November, 1900 
of orthoclase, with calcite, epidote, and more rarely, quartz, 
and titanite. Careful search for albite has been in vain. 
Pyroxene is comparitively rare, having usually altered to 
hornblende.lt sometimes shows remarkably good crystal 
outlines with the common faces: /( 001 ), //'(lOo), ^'(do)' 
m{i\o), and ^^/^(iii). The pyroxene is very pale green to 
colorless and only pleochroic in thick sections, with: 
;/g = cloudy olive green. 
n-m = faintly yellowish green. 
;/p = greenish brown. 
The refringence is very high ; the birefringence is only 
medium with: 
fig - iim = .017 at least. 
Wm - Up — -004 at least. 
iig Up — .021 at least. 
The angle ot the optic axes, as indicated b)' the bire- 
fringence, seems to be unaccountably small; the measures 
of 2^ gives 2E = 56*^ 36'. The maximum extinction angle 
in the vertical zone is at least 45*^. 
The pyroxene does not seem to change to hornblende part 
by part in this rock; but each crystal seems to change grad- 
ually, every part of the crystal changing at once. Thus, the 
mineral may be seen becoming slightly green, then deeper 
green, and finally dark green hornblende appears, which is 
strongly pleochroic, and has changed cleavages and increased 
birefringence. 
The optic properties of this pyroxene suggest that it could 
probably be referred to the abnormal variety, "pigeonite," de- 
scribed above. (See chapter III). 
Magnetite is very rare as an original constituent, and 
usually occurs in very small grains. On the contrary it is very 
.abundant as a secondary mineral. It has been proved repeat- 
edly that this magnetite is titaniferous,* a fact which doubtless 
explains the high per cent of titaniimi in the rock, since the 
pyroxene shows no signs of containing any appreciable 
amount. The octahedral parting and strong magnetic char- 
acter prevent any confusion with ilmenite. 
x}.patite occurs in two different forms between which there 
*See Irving, op. cit. p. 266. 
