Prof. T. G. Bonney—Quarts-Schists from the Alps. 207 
is unconformable with the gneiss, so the question to be determined 
is whether the latter is an older rock than the former, or is an 
intrusive granite which has been afterwards crushed into a gneiss. 
The quartz-schist certainly becomes more micaceous as it approaches 
the gneiss, and I thought that here and there I could detect in it 
indications of larger quartz grains. 
G Gneiss. 
A Gneissose Quartz- 
schist (?) 
C Quartz-schist. 
eeere 
D Cale-schist. B 
we AL! 
G seems to quadrate in A and A into B the last and C are varieties of 
quartz-schist and certainly pass one into the other; the passage from 
C to D about the dotted line is quick. 
Specimens were secured for microscopic examination, which may 
be now described. It will be convenient to take first the normal 
quartz-schist, such as occurs at c in the section, and with this 
specimens of similar rock from other localities may be included. 
These flaggy quartz-schists consist almost entirely of quartz and 
mica, with an occasional grain of felspar, which, however, is some- 
times all but absent... The quartz grains vary in size in the different 
specimens, but are commonly less than :02”. Usually they are 
distinctly longer in the direction of the foliation, their outline is 
irregular, sometimes ragged, giving a characteristic ‘clotted ” look ; 
occasionally, if the nicols be used, one tint, especially where the 
grains run small, seems to predominate in the slide. No trace of 
a nucleus can be detected in the grains, which exhibit the peculiar 
mosaic structure often seen in the more quartzose layers of the mica- 
schists of the same group. Minute fluid cavities with relatively 
small bubbles are rather numerous.? They are more abundant near, 
but not restricted to, the junction of grains. The mica flakes range 
from about :04” downwards in length, being frequently about -03”, 
though in some slides smaller scales, say about ‘01”, are common. 
With transmitted light, they vary from a slightly olive-grey to 
colourless. Dichroism, if any, is very faint; they are, in the 
former case, a little greener with vibrations parallel to the basal 
plane. The ends are often rather irregular, but sometimes the flakes 
1 Small zircons, occasional grains of iron oxide, probably also of zoisite, may be 
detected, but on these it is needless to dwell, as they have no apparent bearing on the 
history of the rock. 
* Most of these require a one-eighth objective and many can only just be seen 
with that; some are irregular in form, the majority oval. 
