198 Canadian Record of Science. 
plates, usually somewhat cloudy from the presence of decom- 
position products. The pyroxene is present in rather sparing 
amount, and is not seen in every slide. It is pale green in 
colour and without noticeable pleochroism, and is inti- 
mately associated wtth the hornblende, being in many 
cases apparently in process of alteration into that mineral, 
as in the case of the Arnprior rock. It may, perhaps, best 
be termed a Plagioclase Scapolite Diorite. 
The rock from the Robertsville Mine is rather coarse- 
grained, and in external appearance bears a strong resem- 
blance to that from McDougall, but possesses a more 
distinct foliation. Under the microscope it is seen to be 
composed of scapolite, plagioclase and hornblende, with 
accessory biotite and epidote. ‘The scapolite is present in 
large amount, and is generally very free from decomposi- 
tion products. It usually occurs in rather large plates, 
which polarize in brilliant colours. The cleavage with 
extinction parallel to it is well seen, and in sections paral- 
lel to the base the mineral is found to be uniaxial and 
negative. The plagioclase, which is also present in large 
amount, polarizes in much more subdued tones. Polysyn- 
theti twinning is seen in many, but not in all cases. It is 
often rendered cloudy by the presence of decomposition 
products, which resemble kaolin in appearance, and as a 
general rule is not so fresh as the scapolite which occurs 
side by side with it. The hornblende, which is light green 
in colour, is without good crystalline form, but is not 
fibrous in character. It is strongly pleochroic, in yellow- 
ish and bluish-green tints. The biotite occurs in very small 
amount, intimately associated with the hornblende and 
partly altered to chlorite. Scattered through the plagio- 
clase, and less frequently also in the scapolite, are many 
small, stout prisms and irregular grains of a colourless 
mineral, with high index of retraction, and which polarizes 
in brilliant colours. Occasionally these are pleochroic, 
with the yellowish tint characteristic of epidote, and have 
been referred to that species. The rock, which under the 
microscope resembles one of the crystalline schists, may be 
termed a Plagioclase Scapolite Amphibolite. 
