105 



and Chrysotile, as well as smaller areas in other parts of 

 the serpentine belt, are composed of serpentine and perido- 

 tite. 



Pyroxenite. — When pure, pyroxenite consists of the 

 mineral pyroxene. There is usually present, however, 

 more or less olivine or feldspar, the former if the rock is 

 approaching the composition of peridotite, the latter if it 

 tends toward gabbro. 



The pyroxenite near the Danville asbestos mines is 

 singularly coarse- textured, and much of it is composed of 

 large pyroxene crystals, some of which measure 2 inches 

 or more on single faces. In general, the pyroxenite is 

 somewhat altered to soapstone. 



Gabbro. — Granitoid rock types in which feldspar is 

 present as well as pyroxene are classed as gabbro. The 

 distinguishing feature of this rock is its coarse texture as 

 exhibited in angular grains of grey feldspar and green 

 pyroxene. It forms a large part of the hills above Lac 

 Coulombre and Nicolet lake, and of Little Ham mountains. 

 It may be seen along the roadside near the southeast shore 

 of Black lake, and in many other places near the foot of 

 serpentine hills. The pyroxene is sometimes altered to 

 hornblende; the rock is then more correctly called a 

 gabbro-diorite. 



Diabase. — The diabase has the same mineral compo- 

 sition as the gabbro, but is much finer grained, and generally 

 has a quite different appearance. It is a fine grained, 

 green rock sometimes snowing small, grey grains of feld- 

 spar. In other cases no individual mineral can be dis- 

 tinguished by the unaided eye. The rock can often be 

 readily recognized by nodules and stringers of yellowish- 

 green epidote, a mineral that has been formed by the 

 alteration of feldspar, and, in part, also of pyroxene. 

 There is frequently a little quartz with the epidote. 



Diabase may be well seen along the Quebec Central 

 railway between Black Lake and Thetford; also near the 

 Roman Catholic church at Black Lake. It forms the 

 hills about Clapham lake, and near the Little Nicolet lakes. 

 It carries copper and iron pyrites, in places, as at Lac 

 Coulombre. In places, by becoming more acid in compo- 

 sition and losing much of its pyroxene, the diabase passes 

 into porphyrite near the outer edges of the mass. 



