182 
hibits marked strain effects. "These vary from the develop- 
ment of undulose extinction. through peripheral shattering to 
complete granulation. 
Felspar is abundant, and is of at least two types. Ortho- 
clase occurs in comparatively large, completely allotriomor- 
phie sections, which are colourless to somewhat cloudy in 
ordinary light. Тһе cloudiness is some of it due to develop- 
ment of kaolin, but some of the secondary material cannot be 
referred to that mineral. The sections are mostly untwinned, 
but a few exhibit twinning after the Carlsbad law. The 
optical properties are perfectly normal, and there is little or 
no trace of shadowy extinction. The difference between the 
refractive index of this felspar and that of quartz is appa- 
rently much greater than that of the other felspar to be 
described. 
The dynamie metamorphism of the rock has caused a little 
shattering of the orthoclase, but far less than in the case of 
quartz. In some instances grains appear to have been com- 
pletely broken up, but mostly the effect is visible only around 
the edge. Some grains of felspar, which.are partly untwin- 
ned, and then indistinguishable from orthoclase, show in their 
remaining portions a very fine, hazy, polysynthetie twinning ; 
others, again, exhibit a similar structure throughout. This 
is extremely suggestive of an orthoclase. 
Albite is present in just about the same proportion as 
orthoclase, and is of the same order of size, and exhibits 
similar strain and decomposition phenomena. Like the or- 
thoclase, it is much less erushed than the quartz, but evi- 
dences of mechanical movements are not wanting in peri- 
pheral shattering and bending and faulting of the twin 
lamelle. The refractive index is slightly lower than that of 
Canada balsam. ‘Twinning after the albite law is seen in 
every instance, the lamelle being narrow and extremely 
regular when not interfered with by mechanical deformation. 
Twinning after the Carlsbad law is by no means common, but 
is readily recognisable in a few instances. Sections perpen- 
dicular to (010) give a maximum symmetrical extinction of 
9°. The extinction is sensibly the same in the two portions 
of a.Carlsbad twin. These measurements indicate albite with 
a composition not far from Ab,, An,. 
The amount of true decomposition in the felspar is com- 
paratively slight. Kaolinization has taken place to a certain 
extent, but not sufficiently to cause more than a cloudiness in 
transmitted light. But the alteration is not confined to 
kaolinization. A large amount of secondary muscovite has 
been produced. This is distributed in the form of small 
flakes throughout most of the sections ої both types of fel- 
