16 PROF. T. G. BONNEY ON THE GEOLOGY 
abundant, a laminated yellowish green mineral occurring in isolated 
folia, in grains exhibiting a marked scaly cleavage, and in felted 
ageregates. Viewed with the polarizer alone, it is seen to be mode- 
rately dichroic, a dull green when the lines formed by the cleavage- 
planes are parallel with the vibration-plane of the transmitted beam, 
and yellow-green when they are perpendicular to it. We may 
safely regard this mineral as a species of the chlorite group. (2) A 
granular mineral, often dusty-looking, giving, when clear, fairly 
bright tints with the two nicols. This I have no doubt is epidote. 
(3) Quartz in rather irregular granules, frequently containing micro- 
liths of a pale green mineral ; some of these, I have little doubt, are 
flakes of a chlorite, but others appear to be belonites, minute elongated 
prisms. The comparative thickness of the including quartz grains 
renders it most difficult to examine their optical characters; but I 
think that the greatest extinction is when the belonite forms a small 
angle with the vibration-plane of one of the crossed nicols, so that 
they are probably hornblende. The quartz also contains numerous 
extremely minute cavities ; these generally seem to be empty, but 
in a very few I have detected little moving bubbles. (4) A mineral 
in grains of moderate size, present, but in variable amount, in most 
of theslides. Ithas one well-marked cleavage, and another making 
with it an angle not far from 90°. It may be orthoclase, but I 
should have expected this under the circumstances to show more 
indication of decomposition, and I should consider that a few earthy- 
looking grains occasionally present are more likely to represent a 
felspathic constituent. The present mineral has considerable resem- 
blance to my specimens of kyanite, which would be a mineral very 
likely to occur in a rock of this nature. Calcite, grains of iron 
Fig. 8.—Section of Chloritic Schist from the west side of Prawle 
Point (Xx 50). 
peroxide, and ferrite stains are occasionally and variably present. 
The quartz granules often have a very clastic aspect, but as they 
contain frequent microliths of the green constituent, I consider this 
illusory, the result of subsequent pressure. It will be remembered 
