7

this band. Argillites near the International Boundary on Salmon river may
also be a continuation of this band. To the southeast the band continues
beyond the area and may join the sediments west of Kitsault river. The
northeasterly band swings northward, becomes much wider in the vicinity
of Glacier and Bitter creeks, but eventually narrows and terminates in the
northern part of the area. Southeastward the band disappears under vol-
eanic rocks in the high mountains at the head of Marmot river.

The southwestern band of the formation on Marmot river is the south-
western limb of a syncline. The prevailing dips are northeasterly, and the
sediments apparently pass under the adjacent volcanic rocks to reappear
and form the northeastern sedimentary band. The small area of sediments
on mount Dolly is in the form of a sharp anticline, the sediments disappear-
ing under voleanic rocks farther up on the mountain. The rocks in this
band are harder than the other sediments in the area, due probably to
thermal metamorphism resulting from batholithie invasion.

The sediments of the northeastern band south of the south fork of
Marmot river lie in a sharp anticline slightly overturned to the west. This
anticline plunges under the voleanic rocks to the south. North of the south
fork overturning is not marked, but the anticline is asymmetric. Farther
north the anticline flattens and the formation broadens considerably. In
the broad part the main anticline becomes two anticlines with a shallow
central syncline, and the whole is complicated by minor folds. Where the
formation plunges under voleanic rocks north of Bear river it is in the form
of a narrow, sharp anticline. The general dip of the western part of the
argillites in the central part of the area is 35 degrees westward. The east-
ern part of the formation was not examined.

According to McConnell the Bitter Creek formation underlies the vol-
canic rocks at the western contact, but appears to overlie similar volcanic
rocks at the eastern contact. He states that parts of the Bear River for-
mation may be contemporaneous with, or even older than, the Bitter Creek
formation.1 Along the western edge of the Bitter Creek formation the
relationship to the overlying volcanic rocks is clearly visible in many
places. The sediments underlie the Bear River formation conformably
and there is a transition zone characterized by interbedding of sedimentary
and voleanic rocks. Dips are rarely seen in the voleanic rocks, but wherever
they were observed they indicated concordance between the two formations.

BEAR RIVER FORMATION

The name Bear River formation was used by McConnell to desig-
nate a series of volcanic rocks exposed in Bear and Salmon River valleys.?
That this name had been used previously for formations of different types
and ages in other places has already been pointed out. However, as the
name is well established in Portland canal it seems advisable to continue
to use it as the name of a formation in that general district.

The formation consists essentially of tuffs, breccias, and lava flows.
A few thin beds of argillite, limestone, and calcareous tuff occur and also

1McConnell, R. G.: Geol. Surv., Canada, Mem. 32, p. 14 (1913)

2McConnell, R. G.: Geol. Surv., Canada, Sum. Rept. 1910, p. 64 (1911).
3Hanson, George: Geol. Surv., Canada, Sum. Rept. 1923, pt. A, p. 35 (1924).