122 CRYSTALINE ROCKS OF N. 8. AND G B.—HONEYMAN. 
I have had sections of the preceding rocks carefully prepared 
by Dr. Alexis 8. Julien, New York. Four of them have already 
been imperfectly examined by an inferior polariscope. I have 
re-examined these thoroughly by the splendid new Polariscope- 
Microscope made by Anderson & Sons, London, for our President, 
and added the other seven to the number; and I propose in these 
notes to give an account of the interesting results and to 
illustrate with the instrument. 
DOLERITES. 
Ist. I begin with the Blomidon Basalt, as this mountain is 
well known wherever Nova Scotian mineralogy is an object of 
study. Its zeolites and other minerals are to be found in all 
great museums, and it is noted in works on general mineralogy as 
one of the principal localities where trappean minerals can be col- 
lected. The section examined is of a compact basaltic prism which 
I picked up at the foot of the mountain in 1875, (a.) Examined by 
the Polariscope, with nzcols crossed, the section is brilliant and 
striking. Revolving the Polariser or Analyser, as both can be 
turned, the change in prismatic colours, and their arrangement is 
kaleidoscopic. The abounding parallel lines with changing and 
alternating colours (trichoic) indicate combinations of crystals into 
twins, three lings and four lings, with chroism of labradorite, 
among these is a constant, unchanging brown colour, ’ this 
distinguishes augite from hornblende, which is dichroic. We have 
thus indicated the two minerals which constitute a dolerite. 
When the nzcols are crossed parts of the section have a vivid 
chromatic polarisation. This is owing to the presence of quartz. 
There is also another obvious constitutent which is opaque. All 
that we can distinguish with the polariscope is the presence of dark 
forms with acute angles or of irregular shape. (b.) Removing 
the polariser and analyser we then examine them in sunshine with 
the microscope, the dark forms are seen to be blue-black in colour 
with metallic lustre. This shows that it is the mineral 
magnetite. Surveying, then, the whole section we find a large 
number of these. At the same time we detect green specks of 
olivine. The basalt is therefore dolerite, consisting of labra- 
dorite and augite with the accidental minerals, quartz, magnetite 
