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regular attitudes. Except within the closely faulted area south of Vega
Creek, there is little angular discordance on each side of the various faults
and shear zones.

Faults and shear zones are numerous in the region between the south
border of the map-area and Vega Creek—too numerous to be adequately
shown on the present map. Most of them are steeply dipping, highly
fractured zones 5 to 50 feet wide, along which both horizontal and vertical
movements have occurred. The breaks trend in many directions, but three
main sets can be recognized: strike north 10 to 30 degrees east, dip nearly
vertical; strike north 30 to 50 degrees west, dip 45 degrees southwest to
vertical; and strike approximately east, dip 60 degrees north to 70 degrees
south. Some of the breaks, in particular those with a northeast trend, show
evidence of at least two periods and directions of movement. All of them
have served as channelways for the circulation of quartz-carbonate solu-
tions, which have altered the adjacent rocks for distances up to 300 feet
to a conspicuous light orange-brown colour, and have filled the fractures
themselves with deposits of ankeritic carbonate and banded chalcedonic
quartz. In places the quartz-carbonate rocks contain much finely divided
hematite. Similar quartz-carbonate mineralization is found, but is much
less abundant, in shear ones in the Takla group rocks in other parts of
the map-area.

ALTERATION AND METAMORPHISM

Virtually all the Takla group rocks have been saussuritized, sericitized,
or carbonatized to some degree. The original rocks, which, whether as
andesite flows, tuffs, or greywackes, were composed essentially of plagioclase
feldspar, hornblende, and pyroxene, have been more or less completely
altered to aggregates of clinozoisite, epidote, sericite, chlorite, and ankeritic
carbonate, with some regeneration of relatively sodic feldspar and uralitic
hornblende. In most rocks, the original textures, and many of the original
minerals or larger fragments, can still be recognized, although the ground-
mass and smaller fragments are almost completely changed. In some of the
quartz-carbonate shear zones, as for example those exposed on Thane and
Vega Creeks, the original rock may be totally unrecognizable, the original
texture obliterated, and the whole rock converted to an indistinct aggregate
of shreds and irregular patches of carbonate, eryptocrystalline to granular
quartz, with minor chlorite, altered feldspar fragments, etc. Except for
these quartz-carbonate shear zones, the degree of alteration is relatively
uniform over the entire exposed area of the Takla group, and does not seem
to be related to the position in the stratigraphic section or to the proximity
of intrusive bodies. The conclusion seems warranted that the whole group
has been subjected to low-grade metamorphism involving some metasomatic
change; a change that may be partly autometamorphic, connected with the
consolidation of the original rock.

Throughout the entire length of its exposure in Aiken Lake map-area,
the Takla group is invaded by various bodies of the Omineca intrusions,
chief among which is the Hogem batholith. Despite the intimate association
with intrusive rocks, contact metamorphic effects traceable to these bodies
are almost negligible. Careful field observation and study of thin sections
has shown no change in any of the Takla group rocks to within 300 feet
of the contact with the batholith, and in many places there is no discernible