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corner of Aiken Lake map-area belong, a lithological division comprised ae of greenstone appears to be the youngest of the group (Armstrong,

The Cache Creek group rocks are not known to be in exposed contact with any other rock unit in Aiken Lake map-area. They strike directly toward the Ingenika group rocks on the north side of Osilinka River Valley, and are probably separated from them by a fault. They are in places parallel with, and in places in marked discordance with, the banded tuffs and andesite flows of the late Paleozoic map-unit to the west. In part these two map-units are almost certainly separated by a fault, but it is possible that they may be in part conformable, or even parts of the same Cache Creek group assemblage, in spite of a lithological dissimilarity. The struc- tures within the Cache Creek group rocks west of Wasi Lake, near the contact of the group, are consistent with the possibility that the banded tuffs and other rocks to the west could have been thrust up relative to the Cache Creek beds, into their present position along an essentially dip-slip fault striking north 15 degrees west and dipping about 50 degrees southwest.

AGE

Fossils have been collected from the massive blue-grey limestones east of the Weber group of mineral claims, on ‘the east boundary of the map- area, and from the lower limestone belt exposed 5 miles east of the map- area. These fossils have been examined by P. Harker of the Geological Survey, who states that the precise identification and assignment of definite stratigraphic horizons must await further studies of the late Paleozoic fauna of northwestern Canada as a whole, but that the collections include pro- ductid brachiopods of undoubted Pennsylvanian or Permian ‘age.

The rocks southwest of Omineca River are part of an assemblage that, in the Fort St. James map-area to the south, includes foraminifera of Middle Permian age (Armstrong, 1949).

CoRRELATION

The Cache Creek group, named by Selwyn (1873, pp. 60-62) from its typical occurrence around Cache Creek, near Ashcroft, in southern British Columbia, and to which Selwyn (1877, p. 78) and Dawson (1878, p. 55) assigned the limestones near Stuart Lake in the Fort St. James map-area, has been redefined by Armstrong (1949, p. 50) as: “a very thick assemblage of interbedded sedimentary and volcanic rocks, mainly of Permian age, but also probably in part of Pennsylvanian age. The whole of the Permian period may be represented. Foraminiferal limestones and ribbon cherts are characteristic of the group”.

The rocks in the southeastern corner of Aiken Lake map-area are the northwesterly continuation of strata that, in the Manson Creek map-area to the southeast, have been correlated by Armstrong and Thurber (1945) with the Cache Creek group on the basis of lithology and stratigraphy. The beds and flows in the southwest corner of the map-area belong to an assem- blage that contains typical Pennsylvanian(?) and Permian foraminifera,