The Long Labrador Trail Part 21

Forty-six miles above Seal Lake an exposure of phyllite was seen, the same in every respect as the one east of Seal Lake, just mentioned.

The general direction of foliation is S. 70 degrees E. and the dip 70 degrees. The higher hills west of Seal Lake are capped by a much altered gabbro [13] that has undergone considerable weathering.

Between the Nascaupee River and a few miles beyond Bibiquasin Lake the rock is quartzite, [14] considerably weathered and covered by drift.

Bowlders of this quartzite were seen along the Nascaupee River long before the first outcrop was reached, showing the general direction of the glacial movement to have been to the southeast. From Bibiquasin Lake to Lake Kash.e.s.h.ebogamog the country is covered with much drift; the only exposures are on the steep hillsides. The rock being a coa.r.s.e hornblende granite.

The western end of Kash.e.s.h.ebogamog Lake lies within the limit of the anorthosite [15] area, which extends from that point to Lake Michikamau, a direct distance of twenty miles and was the only anorthosite observed on the journey.

GLACIAL STRIAE

First portage opposite Red River S. 45 degrees E. On Caribou Ridge E. At Washkagama Lake S. 70 degrees E. Near Seal Lake N. 85 degrees E. At Wuchusk Nipi S. 75 degrees E.

Thirty-two miles above Wuchusk Nipi S. 70 degrees E.

MICROSCOPICAL FEATURES OF THE ROCK SPECIMENS

By G. M. Richards, Columbia University 1--Pegmat.i.te-Grand Lake. The specimen was taken from a pegmat.i.te dike at its contact with an amphibolite. In the hand specimen it is an apparently pure orthoclase but in the thin section small scattered quartz grains are observed; as well as the alteration products, Kaolin and sericite.

The minerals at contact are quartz, biot.i.te, magnet.i.te and hornblende.

Both the quartz and orthoclase contain dust inclusions and crystallites, while the evidences of shearing and crus.h.i.+ng are abundant.

2-Quartz Biot.i.te Schist.

Contact between above dike and amphibolite. A coa.r.s.e black rock carrying magnet.i.te and pyrites in considerable quant.i.ties.

Under the microscope some of the biot.i.te has a green coloration from decomposition and is surrounded by strong pleochroic halos.

Small grains of secondary pyroxene are numerous.

AMPHIBOLITE

3-Grand Lake.

A dark, compact rock, having a mottled appearance due to grains of plagioclase, and a green color in section.

Minerals present are hornblende, biot.i.te, plagioclase, pyroxene, quartz and the alteration products from the feldspar.

The rock has been subjected to a strong crus.h.i.+ng action, which has been resisted by only small portions of it. The s.p.a.ces between the grains, which are intact, are filled with a confused ma.s.s of peripherally granulated minerals, in which strain shadows are very prominent.

The rock has been derived by dynamic metamorphism from a basic igneous rock.

4-Biot.i.te Granite Gneiss.

Eighteen miles above mouth of Nascaupee River. A fine-grained rock of gneissic structure having a faint pink color.

Plagioclase, microcline and quartz are the predominating minerals, while biot.i.te, t.i.tanite, epidote, apat.i.te, zircon and garnet are present in smaller quant.i.ties.

There is also a small amount of hemat.i.te, pyroxene and sericite.

The rock, which is of a granitic composition, contains numerous crystallites and has been subjected to considerable strain and crus.h.i.+ng, which has resulted in foliation.

5-Mica Granite Gneiss--Country Rock--near Caribou Ridge.

In the hand specimen the rock has the same appearance as No. 4, if anything, it is somewhat more compact.

The princ.i.p.al minerals are, plagioclase, biot.i.te and microcline, with smaller quant.i.ties of quartz, iron oxide, pyroxene and garnet.

The feldspar is decomposed with the resulting formation of epidote, which is quite prominent. There are also numerous included crystals.

The rock has been greatly crushed and sheared, and is much finer than No. 4.

6--Cap of Caribou Ridge.

A hard compact rock of dark green color, having a mottled appearance, due to the presence of a white mineral.

Pyroxene, quartz and augite form the groundma.s.s, as seen in section.

There are a few small grains of magnet.i.te.

The severe crus.h.i.+ng to which the rock has been subjected has resulted in the conversion of the plagioclase into scapolite and also in the formation of zoisite by the characteristic alteration of the lime bearing silicate of the feldspar in conjunction with other const.i.tuents of the rock.

The light mineral is finely granulated and the whole is marked by uneven extinction.

The rock has probably been derived by dynamic metamorphism, from a coa.r.s.e igneous rock like a gabbro.

7--Epidotic Sericitic Schist. Washkagama Lake.

A fine grained compact gray rock, of aggregate structure, consisting chiefly of quartz, plagioclase and biot.i.te, and the alteration products epidote and sericite.

Under the microscope it is a confused ma.s.s of finely granulated minerals, with numerous included crystals.

The rock has undergone complete metamorphism and its origin is unknown.

8--Phyllite-Near Otter Lake.

A soft extremely fine grained gray rock, with a well developed schistose structure, carrying much magnet.i.te, plagioclase, orthoclase and their alteration products.

The strain to which the rock has been subjected has resulted in a very fine lamination, and it is _considerably weathered_.

9--Calcarous Sericite Schist.--Seven Miles East of Seal Lake.

A dark compact rock, in which calcite and sericite predominate. Quartz is less plentiful. The results of shearing and pressure are very prominent and bring out the foliation, even in the calcite.

10--Schistose Limestone--Same location as No. 9.

A white rock having a peculiar mottled appearance due to the inclusions of decomposing biot.i.te which project from the surrounding ma.s.s of calcite. There is some sericite present, also magnet.i.te, resulting from the decomposition of the biot.i.te.

The bent and metamorphosed condition of the calcite shows the shearing and crus.h.i.+ng which the rock has undergone.