200 Canadian Record of Science. 
of the Laurentian System. There are, however, many 
amphibolites and dioritic rocks occurring in the same 
district intimately associated with these limestones, but 
which contain no scapolite whatever. There is, for 
example, a great thickness of amphibolites, interstratified 
with crystalline limestone, exposed on the north shore of 
the Ottawa, just below the town of Arnprior, which we 
examined some years ago when on a visit to that locality 
for the purpose of endeavouring to discover the Scapolite- 
Diorite in place. They are all rather fine-grained and 
weather dark gray and black, and have a more or less dis- 
tinct foliation. They were followed for a distance of about 
five miles below Arnprior, being gradually replaced by 
quartz feldspar rocks. Like all the other amphibolites and 
dioritic rocks of the district which do not hold scapolite, 
when examined with the naked eye the feldspar is seen to be 
wanting in that peculiar bluish-white tint characteristic of 
the scapolite, and which the Norwegian geologists com- 
pared to wet snow. Three specimens, collected respec- 
tively a quarter of a mile, two and a quarter, and three 
and a half miles below Arnprior, were sliced and exam- 
ined. The last of these is traversed by little pegmatite 
veins, and under the microscope is found to be composed 
of hornblende, biotite and plagioclase, with accessories of 
epidote and sphene. The hornblende is green in colour, 
strongly pleochroic and without any tendency to a fibrous 
structure. It occurs in irregular shaped fragments, which 
occasionally have an imperfect idiomorphic development, 
and which mark the lines of foliation. The biotite, which 
is present in much smaller amount than the hornblende, is 
brown, with the usual strong dichroism and parallel extinc- 
tion. The plagioclase is generally twinned, the lamelle 
being narrow and the twinning generally faint. All un- 
twinned grains which could be found cut in a direction at 
right angles to an optic axis, showed the revolving bar of a 
biaxial crystal. They polarize in rather dull tints, and 
extinguish simultaneously over the whole surface, showing 
little or no evidence of having been submitted to pressure. 
