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opaque milky white veins typical of the Tenakihi rocks. Most of them are
lenticular, less than 200 feet long, and follow bedding planes in rocks of the
more brittle types. Veins less than 2 feet thick are uncommon. As in the
Tenakihi group, these veins are thought to be mainly a by-product of
regional metamorphism, rather than the result of later hydrothermal proc-
esses. Some of the quartz in the veins cutting Ingenika group beds may
have been derived from Tenakihi rocks.

RELATION OF METAMORPHISM TO DEFORMATION

That the metamorphism of the Ingenika group rocks occurred mainly
prior to the development of the present folded structures is apparent from
the general correspondence between the metamorphic grade and strati-
graphic horizons, independent of the present attitude of the rocks. If the
increase of metamorphic grade is acknowledged to be dependent upon an
increase of temperature and pressure determined in part by depth of burial,
combined with high shearing stress, then clearly the metamorphism could
not have taken place during the time the rocks were being folded to their
present positions, nor at any time since they had attained these positions.
To cite an extreme example, in the overturned beds on the west flank of
the Butler Range, the garnetiferous schists of the Tenakihi group and the
quartz-biotite schists of the Ingenika group on the crest of the range lie
structurally on top of the chloritic phyllites and slates that are more
intensely deformed, but of lower metamorphic grade, at the base of the slope.

The relation between schistosity and bedding in the Ingenika group is
similar to that in the Tenakihi group; the general plane of schistosity is
parallel with both the limbs and crests of the major and most of the minor
folds, but cuts across some of the minor folds. The planes of schistosity
and cleavage are for the most part rigorously parallel with the bedding in
rocks free from intense local contortion, but where the beds are strongly
drag-folded on a small scale, shear and platy cleavage planes parallel the
axial planes of the small folds. In some such instances the attitude of the
plane of shearing changes as much as 90 degrees within 500 feet. Ina few
places, where the axial planes of the drag-folds are sharply bent, or where
the minor structures are domes and basins superimposed on more regular
folds, the rock possesses two sets of shear planes about equally developed—
one parallel with the bedding and one parallel with the axial plane of the
fold—and the disintegrated rock is an aggregate of pencil-like fragments.

Further evidence that metamorphism and development of schistosity
had occurred to some degree before the last major folding of the rocks is
afforded by the limestones east of Pelly Creek, which have been folded
into isoclinal, digitate folds more than 2,000 feet from crest to trough. Near
timber-line on the southwest shoulder of the mountain south of Pelly Lake,
a series of such limestones is well bedded, slightly micaceous, with a faint
but unmistakable schistosity parallel or nearly parallel with the bedding.
The rock is cut by subparallel, nearly plane, calcite veins, mainly less
than 6 inches but in places up to 10 feet thick, that are so numerous that
on some exposures vein material comprises an estimated 20 per cent of the
rock volume. The veins occupy simple fissures, which lie at an average
angle of about 10 degrees to the bedding plane (bedding and schistosity