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individual outcrops of each group are in many instances lithologically
similar. In the southern part of the map-area the contact has been placed
below a band of conglomerate exposed west of Uslika Lake and on Thane
and Vega Creeks, and containing pebbles of banded tuff and of intrusive
rock not unlike that composing some of the pebbles in one of the bodies
of conglomerate in the Lay Range. In other respects these conglomerates
are not at all similar. The conglomerate west of Uslika Lake lies above
a fault or a pronounced angular unconformity. On Tutizika River, and
down almost the entire length of Lay Creek Valley, a well-exposed fault
zone is believed to mark the contact.

METAMORPHISM

Almost all these late Paleozoic rocks are composed in part or entirely
of volcanic material; the andesitic flows, breccias, tuffs, and greywackes
have been altered by the processes of chloritization, propylitization, and
saussuritization to aggregates of chlorite, sericite, epidote-clinozoisite, clay-
like matter, and minor calcite and pyrite. The change appears to have been
essentially one of introduction of water, with some sulphur and carbon
dioxide, to the rocks. The dark minerals have been most severely altered;
in nearly all rocks the pyroxenes have been almost completely changed
to amphibole, or chlorite, or both, and in many specimens the original
presence of phenocrysts of pyroxene or amphibole can only be recognized
by the occurrence of crudely polygonal clusters of chlorite, needle-like
amphibole, and grains of clinozoisite. The feldspar crystals are more
resistant to alteration in these rocks, and in a few specimens are quite
fresh; most of them, however, are partly to completely saussuritized. In

most rocks phenocrysts and groundmass appear to have been about equally
altered.

The intensity of this alteration does not appear to be related to any
of the recognized shear and fault zones, or to the numerous bodies of
intrusive rocks, but is mainly restricted to volcanic material, and seems
to be a normal autometamorphic process (propylitization) consequent on
consolidation and cooling of the voleanic matter. The presence of pro-
pylitized fragments of andesite and tuff in greywackes containing recog-
nizable organic remains suggests that the alteration took place in each
flow and tuff bed individually, as it consolidated, before its fragmentation
and transportation to the greywacke bed. That the alteration was facili-
tated by solutions that circulated along joints in the rock is indicated by
the abundant coating of serpentine-like material, some of which is typical
antigorite, on fracture surfaces. The larger fractures apparently did not
serve as channelways for widespread movement of the solutions; very
few shear zones are serpentinized.

The rocks of non-voleanic origin are fresh. All the limestones are
partly recrystallized. The sandstones and grits are composed mainly of
metamorphic materials, and have been unaffected by any processes to