14 
of the field. The size and shape of the constituent indi- 
viduals of plagioclase and their polysynthetic twinning 
are well seen. The rock is composed almost exclusively 
of this mineral, the individuals of which are neither bent 
nor twisted, and no strain-shadows are to be observed. 
(b) In this section, which was prepared from a speci- 
men collected about three and a half miles north-east of 
White Lake, in the front of the township of Chilton, a 
distinct breaking or granulation of the plagioclase can be 
observed, especially in the lower portion of the slide, 
while the same process can be elsewhere seen, though not 
so well marked. The large plagioclase individuals no 
longer meet along clear well defined boundary lines, but 
are irregular in shape, cracked, and separated from one 
another by a mosaic of broken grains. Strain-shadows, 
twisted twin lamellae and other evidences of pressure are 
well shown. The rock shows no distinct foliation or 
banding. 
(c) The third section shows the appearance presented 
by a highly granulated variety of the anorthosite under 
the microscope. This specimen was obtained from the 
arm-like extension of the anorthosite mass before mentioned 
near its western contact with the gneiss, on range XI of 
the township of Rawdon. In this section, about one-half 
of the field is occupied by broken grains of plagioclase, 
while in the middle is a large plagioclase individual in 
process of destruction. A line of granulated material is 
being developed in a longitudinal direction through the 
large crystal, making, as is usual, an angle of about 20° with 
the lines of twinning, and which, if continued, would cut 
it in two; while little fragments of the plagioclase can be 
seen about its edge in the very act of breaking off—first 
a strain-shadow (excellently seen on the upper edge of the 
large individual) appearing, then a curved crack extending 
in from the edge of the crystal, and finally the breaking 
away of the small piece of the mineral, leaving an irregular 
indentation. The appearance is precisely that which the 
mineral would present if little pieces were being broken 
off the edge with a pair of small pincers. The strain 
having been relieved by fracture, all evidence of pressure 
disappears in the broken grain. If a thin section were 
composed of broken grains alone, it would be impossible 
in most cases to determine that these had resulted from 
the breaking down of larger individuals. This rock is 
