5

South of the Cassiar batholith the stratigraphic sequence is not as well
known. Structural evidence suggests that the thick, massive limestones
on the southern edge of the belt of sediments are the lowest members
exposed. Near the headwaters of Goldpan creek these limestones are
separated from the overlying argillaceous sediments by a limestone boulder
conglomerate. This conglomerate was not seen in the mountains east of
McBride river so it may be local in extent.

Above the conglomerate and limestone is a series of thinly bedded
argillites, argillaceous quartzites, and slates. These rocks are brown to
black and possess a marked slaty cleavage. Southeast of the headwaters
of Hagle river there appears to be a gradual transition along the strike
from these clastic sediments on the west to limy sediments and cherts
on the east.

In the vicinity of Dome mountain the argillites contain intercalated
massive beds of arkosic sandstone. The sandstones are usually light grey-
ish green on a fresh fracture, and many contain small flakes of carbon-
aceous material. Rocks of similar lithological character are seen on the
ridge southeast of Eagle lake and also near the summit of Tanzilla butte.
Under the microscope these sandstones are seen to be quite similar in
mineral content and appearance. The most abundant constituents are
angular to subangular grains of feldspar (orthoclase and plagioclase) and
quartz. There are, as a rule, a number of rock fragments present, some
of which are fine-grained feldspar porphyries; others are granitic in
appearance; and still others are made up mainly of calcite. Larger frag-
ments of these same rock types make up pebble and cobblestone con-
glomerates which are closely associated with the sandstones. Both the
sandstones and conglomerates are thoroughly indurated and in places
slightly sheared. Squeezed and elongated limestone boulders in the con-
glomerates have their long axes parallel to the dip of the beds.

The thickness of the northern band of the Dease series, judging from
dips across a width of 8 miles, is about 15,000 feet. Only a very rough
estimate can be made of the thickness of this series on the south side of
the Cassiar batholith. The maximum thickness of the different members
includes 3,000 feet of massive limestones, 500 feet of limestone con-
glomerate, 4,000 feet of ‘argillite and arkosic sandstone, 8,000 feet of thinly
bedded argillite, slate, and argillaceous quartzite, and 500 feet of massive
marble included in a large body of serpentine, or a total maximum thick-
ness of about 16,000 feet.

Several patches of highly metamorphosed sediments within the batho-
lith have been mapped as Dease series.

The age of the entire series has not been established. Permian fossils
were found in Dease Lake area by Kerr. Fossils of probable Silurian age
were collected in the northern part of the Eagle-McDame area. Several
thousand feet of sedimentary rocks are present below the Silurian horizon,
so it would seem that much of Paleozoic time is represented. Kerr found
Triassic fossils in limestones above serpentine believed by him to be an
altered basic lava. The writers also found bands of serpentine but believe
they are altered basic intrusive rocks. Because of this interpretation it
is impossible to regard the serpentine as a definite horizon marker
throughout the area and to consider the underlying rocks Paleozoic and