103

somewhat elongate, fluidally arranged amygdules up to one-half
inch long and filled with chlorite, calcite, and common opal.

In thin section the essential minerals are plagioclase and
augite, both greatly altered, though with the habit of those
minerals as in the other basalts. Secondary minerals are
chlorite and calcite in large amounts, limonite, sericite, kaolin,
etc. The texture of the massive portion of the rock is very
finely granular and the alteration, in contrast to the other
basalts, is great.

A boulder found in the Baddeck river consists of a dark
green, highly amygdaloidal rock, crowded with spherical amyg-
dules of chlorite, some of them concentrically arranged.

Under the microscope, the original minerals of the rock
are seen to be entirely altered and recrystallized to a finely
granular mass of euhedral to subhedral epidote and chlorite.
The amygdules originally filled with chlorite have been re-
crystallized and are more intimately bound up with and grada-
tional into the solid portion of the rock. Not a trace of any
primary mineral was noted. Besides epidote and chlorite,
limonite and probably magnetite dust occur. The alteration
is, of course, extreme; and it is significant that the only cases of
considerable alteration seen in the basalts have taken place in
these, originally porous rocks. The high degree of recrystalli-
zation in this rock, which is probably a surface flow, is evidence
that hydrothermal action acted inan especially severe manner; and
the rock may belong to the Yakoun formation, though found in
an area underlain by Masset basalt flows.

Quartz Basalt. A specimen collected from the east shore of
Yakoun lake is remarkable on account of the quartz it contains.
It is a grey, dense rock.

In thin section, labradorite and augite are the essential
minerals, with subordinate quartz and magnetite. The usual
calcite, chlorite, etc., are found secondary. The labradorite
forms laths with irregular ends, averaging 0-4 by 0-05
mm. The mineral is so unaltered that only a little kaolin has
been noted. The augite, on the other hand, is virtually all
altered to a scaly and granular mass of calcite with a little
chlorite. Quartz is found in equant, irregularly anhedral