8 
MUSEUM BULLETIN NO. 27. 
the outlines of the original crystals may be frequently traced; minute 
veinlets of parallel fibres of chrysotile may traverse these, marking, no 
doubt, the positions of cracks in the crystals, along which the serpentiniz- 
ation commenced. Otherwise, the serpentine fibres have no regular 
orientation, and the material exhibits the usual aggregate polarization. 
The pyroxene, always present in small amount, is seldom completely 
altered, and frequently is only very little changed. Grains of iron ore 
are disseminated throughout the rock in much the same manner as that 
in which they occur in the original peridotite. 
PYROXENITE. 
When the rock contains more pyroxene than olivine, it is named 
pyroxenite, and it is with a rock intermediate in composition between 
pyroxenite and peridotite that the chromite ore-bodies are associated. 
The pyroxenite is a dark green rock, and it is often very coarsely crys- 
tallized, as for example near the Danville asbestos mines, where the 
constituent pyroxene crystals commonly show cleavage faces 2 inches 
across, and occasionally as large as 5 inches by 8 inches. The pyroxene, 
which is by far the most abundant mineral, is largely diallage, although 
numerous crystals have the optical character of enstatite, and others 
of augite. There are subordinate amounts of olivine and of plagioclase 
feldspar, the rock passing with increase of the plagioclase into gabbro. 
GABBRO. 
The coarse-grained types which are composed essentially of pyroxene 
and plagioclase are classed as gabbro. This type of rock is commonly 
met with between the pyroxenite and diabase; it may be seen exposed 
along the roadside near the southeast shore of Black lake, and in many 
other places near the foot of the serpentine hills. The rock consists of 
grey plagioclase and green diallage; but in place of the latter it may con- 
tain colourless hornblende, which is apparently secondary, and the rock 
may then more properly be called a gabbro-diorite. 
DIABASE. 
x 
The diabase has the same mineral composition as the gabbro, but 
is greyish-green in colour and fine-grained, sometimes so much so that 
no individual minerals can be distinguished by the unaided eye. Its 
recognition in the field is usually facilitated by the occurrence throughout 
the rock of yellowish-green streaks and spots, very conspicuous on weath- 
ered surfaces, of epidote, which has been derived from the alteration of 
plagioclase, and, in part also, of pyroxene. Examination of thin sections 
shows the diabase to be always rather highly altered, the original primary 
