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Johanson Lake small areas of altered tuff and agglomerate contain a few
rounded to angular bodies of fine-grained grey limestone from 1 inch to 18
inches long. Microscopic examination shows that, in addition to the grains
and phenocrysts of hornblende and augite, these formations contain various
proportions of plagioclase, fine-grained, fibrous hornblende, chlorite, calcite,
ankerite, clinozoisite, quartz, black metallic iron minerals, and epidote.
The plagioclase forms ragged, twinned, saussuritized crystals, some of
labradorite but many probably of andesine.

Greenstones. The greenstones are fine- to medium-grained, altered
volcanic rocks containing highly altered feldspar, chlorite, epidote, and
other minerals. Although doubtless derived from the same rocks as the
meta-andesites and meta-basalts, alteration has been more complete, and
has obliterated most of the original internal structures and textures.

Basalt. An unusual type of coarsely porphyritic basalt outcrops on
the southern end of McConnell Range. It contains numerous laths of
altered labradorite, from 4 inch to 14 inches long, set in a dense, purplish
red, brown, or green groundmass. Here and there it is interlayered with
a little finely bedded, red-brown tuff. In places it is a lava, as evidenced
by epidote amygdules, but elsewhere these features were not observed and
it may be that the rock is in part intrusive. Very similar rock forms a
few of the fragments in the associated meta-andesite and meta-basalt
agglomerates, and in the less altered andesitic and basaltic agglomerates
between Sustut and Niven Peaks. Certain varieties on the southern part
of McConnell Range contain 4-inch labradorite laths and $-inch pheno-
erysts of pyroxene or hornblende, and may represent a phase of basaltic
lava intermediate between the porphyritic basalt and the more common
meta-andesite, which normally contains no conspicuous feldspar pheno-
erysts. The coarsely porphyritic basalt is provisionally assigned to the
upper part of this group of altered volcanic rocks because it appears to
be in part interlayered with meta-andesite and, nearby, immediately under-
lies voleanic formations thought to be of Jurassic age.

Hornblende Schist and Gneiss. These are fine to medium-grained,
dark green to nearly black, foliated or banded rocks that, although derived
mainly or entirely from the same volcanic group as the meta-andesites
and associated rocks, into which they grade, have been markedly sheared
and more or less completely recrystallized. They were found mainly near
the larger granitic intrusions, as along and east of McConnell Creek, on
Wrede Range, on either side of Dortatelle Creek, and thence southerly
towards the north fork of Carruthers Creek. The most highly altered,
eneissic phases generally lie within a few thousand feet of the borders of
these intrusions, but not all rocks at such localities have been altered to
this degree. The schists derived from tuffs show occasional traces of
bedding, whereas some of those formed from agglomerates contain vague
streaks and lenses resulting from the mashing and recrystallization of the
agglomerate fragments. The microscope shows the schists to be composed
mainly of fibrous, strongly pleochroic hornblende and andesine, and a little
epidote. The gneisses are recrystallized rocks made up of lenticles, and
bands as much as several feet wide, composed of amphibole and andesine
in various proportions. Where they have been completely recrystallized,