4

Lang, Trout, and Quartz creeks flow southeast and south and become
McDame creek below their junction. The broad Cottonwood glacier,
entering this valley from the side, because of its larger feeding ground
persisted in its flow after the ice had receded out of the upper Lang, Trout,
and Quartz Creek valleys. The presence and final disappearance of this
ice stream led to interesting adjustments in drainage. Shore-lines mark
a lake level on Trout creek 300 to 400 feet above the present floor of the
creek. The lake was evidently backed up behind ice that could enter only
through the Cottonwood pass. Lang creek flowed out toward Trout creek
along the side of this ice and cut a channel that is now on the hill-side and
built up a large, flat fan of gravel 200 feet deep, in Trout Creek lake. Lang,
Trout, and Quartz Creeks’ waters flowed around the north side of the glacier
and cut a similar channel on the hill-side between Quartz and Snow creeks
and also for a short distance below Snow creek. As the ice melted the
drainage of Snow, Quartz, and Lang creeks became gradually adjusted to
their present channels and this adjustment is marked by at least four
abandoned stream channels north of the present junction of Quartz and
Trout creeks.

GEOLOGY

On the geological map the rocks of the area are grouped in five map
units. The oldest unit is the Dease series consisting of quartzites, lime-
stones, and argillites. These sediments are succeeded by the McLeod
series of flows, fragmentals, sediments, and intrusives. Serpentine occurs
at and above the base of the McLeod series, and in some places in the
upper part of the Dease series. Part of the serpentine is mapped as a
separate unit, but some of it is included in the McLeod series. The granitic
Cassiar batholith intrudes the rocks already mentioned. Lavas and frag-
mental rocks of Pleistocene age occur in a few places.

DEASE SERIES

Rocks of the Dease series form wide, northwesterly trending bands
on the north and south sides of the Cassiar batholith. The series is sedi-
mentary and consists largely of limestone, thinly bedded argillite, quartzite,
and chert. Coarser clastic sediments include fine- to coarse-grained, arkosic
sandstone and some cobblestone conglomerate. Adjacent to intrusive
bodies of serpentine the argillaceous sediments and limestone have been
recrystallized to mica schists and coarse-grained marbles.

On the north side of the Cassiar batholith the lower part of the series
consists of quartzite and argillaceous quartzite. These rocks are fine to
medium grained and white to light grey. Quartzite, argillite, and thick
bands of white limestone, up to 500 feet thick, characterize the middle
part of the series. Several thin bands of white to grey limestone at
McDame are oolitic. The quartzite and argillite commonly contain cal-
careous cement. Limestone, argillite, and banded chert constitute the
upper part of the series. The limestone is white to tan and occurs in bands
up to 50 feet thick. Banded chert, made up of alternating thin bands of
chert and argillite, and having a thickness of about 500 feet, forms the
top of the series in some places. At McDame it is overlain by argillite
and on Sheep mountain by quartzite.