Stops Of Interest: LABRADOR
Stops in southeast Labrador are reached by ferry from St. Barbe to Blanc
Sablon, Quebec, and then by Route 510
- Gulf coast, Labrador
- Reef fossils, L'Anse-Amour
- Sandstone and gneiss, L'Anse-au-Diable
- Gneissic granite, Capstan Island to Red Bay
- Red Bay area
- "Devil's Dining Table"
- Gneissic granite, Mary's Harbour
- Deformed gneiss, St. Lewis (Fox Harbour)
- Mafic gneiss, Port Hope Simpson
- "Hole in the Wall"
- "American Men"
- Gneiss and gabbro, Black Tickle
- Gneiss and gabbro, Horse Chops Island
- Porcupine Strand, North Strand
- Lake Melville rift valley from Lake Melville
- Grenville-Makkovik province boundary at Smokey
1. Gulf coast, Labrador
Although Basque whalers spent summer seasons on this
coast in the 16th century, permanent fishing communities were not
established until the early 1700s. These are in sheltered bays where
freshwater streams flow into the sea. The coastal highway, constructed
in the mid-1980s, crosses the headlands high above sea level and cuts
down through the bedrock in long slopes to reach the communities. This
allows excellent viewing of local geology. Warning! The shoulders of
the road are narrow on most slopes. Do not block traffic.
From Blanc Sablon to Capstan Island, the sea cliffs and flat-
topped hills consist of Cambrian conglomerate, sandstone, shale, and
limestone that lie unconformably on Middle Proterozoic gneissic granite
of the Grenville Province. The sedimentary rocks were deposited in
riverbeds and in a shallow sea at the northwest margin of the Iapetus
Ocean (see Plate Tectonics panel). The thick lower sections in the long
sloping roadcuts are mainly sandstone. Thinner beds of shale and
limestone overlie the sandstone, and can be seen near the L'Anse-Amour
lighthouse and in quarries at higher levels.
2. Reef fossils, L'Anse-Amour
The Point Amour lighthouse offers a scenic
view from fossil-bearing cliffs. You can also see the remains of the
British light cruiser, HMS Raleigh, wrecked on this point in 1922 with
the loss of eleven lives.
Take the turnoff to L'Anse-Amour between Forteau and L'Anse-au-
Loup, drive about 4 km, and park near the lighthouse. Walk down and
along the shore to see fossils in the rocks on the beach and in the
cliffs behind it.
Rock types include pink and red sandstone, red to purple mudstone,
and medium- to thin-bedded grey and orange-weathering limestone. The
purple mudstone contains rings and irregular blebs or fragments of white
calcite. These are the remains of now-extinct, primitive organisms
called archeocyathids, which once formed reefs similar to modern coral
reefs.
Near the lighthouse, in the orange-weathering limestone, there is
a large mound that formed as a reef in the Cambrian sea. Within the
reef are layers and irregular masses of archeocyathids, which include
pieces shaped like sticks, cups and plates. There are also other
fossils and thin layers of sediment. The bedded grey limestone below
and around the reef consists mostly of crinoid fragments. Crinoids are
extinct; they looked like sea urchins but were anchored to the sea floor
by long stems. Masses of crinoids resembled flowers growing in
submarine "meadows" and they surrounded the archeocyathid reefs in the
shallow sea. The fine-grained, grey limestone consists of millions of
broken pieces from the stems and heads of dead crinoids.
3. Sandstone and gneiss, L'Anse-au-Diable
Just west of L'Anse-au-Diable,
the highway forms a long switchback which exposes more than 150 vertical
metres of Cambrian sandstone, as well as underlying Middle Proterozoic
gneissic granite. The orange to pink gneissic granite is seen along the
valley floor and the farthest inland curve. It was metamorphosed and
deformed during the Grenvillian Orogeny, about 1000 million years ago,
and uplifted to form part of an ancient mountain range. The mountains
were then eroded almost level before the sandstone was deposited on top
of the gneissic granite in riverbeds and in a shallow sea.
Unfortunately the unconformity between the gneissic granite and the
sandstone is not exposed at this location.
The lowest sandstone, close to the bottom of the hill, is the most
coarse-grained in the section. Westward up the hill, vivid purple, red
and buff coloured sandstone beds alternate; some of the bedding planes
are curved, reflecting the scouring action of strong, variable currents
that deposited the sand. The sandstones are mostly crossbedded, another
indication of strong currents. The often paler coloured, thicker beds
tend to contain less mud, and some have fossil worm burrows. The
colours and variety of patterns are spectacular. The purples and reds
are a result of oxidation of iron in the sand around the time of
deposition.
Toward the top of the hill, the beds are thinner and shaly. These
finer grained sediments were deposited in deeper water as the sea
invaded farther inland.
4. Gneissic granite, Capstan Island to Red Bay
From Capstan Island to Red
Bay the roadcuts are made of Middle Proterozoic gneissic granite, which
is red, orange and pink and grey, and often shot through with black
diabase dykes and white quartz veins. Pink and grey gneisses create
startlingly beautiful abstract patterns. They indicate that high
temperature and pressure acted on these rocks, melting, squeezing,
remelting, and forcing molten rock along new cracks. These are the deep
roots of the Grenvillian mountain range, exposed by erosion. Caution!
The shoulders of the highway are narrow. Do not park on blind or
restricted curves.
Note the deep-red colour of sand along the road east of Pinware.
The sand was derived by glacial erosion of the red gneissic granite
bedrock, and deposited by glacial meltwater in this broad valley. Work
crews have used it to fill and smooth excavations during road and sewer
construction in West St. Modeste.
By contrast, the sand banks and dunes west of L'Anse-au-Loup are a
pale, delicate pink. They were derived from the paler buff, red and
pink Cambrian sandstones.
5. Red Bay area
The uplands surrounding Red Bay are composed of bright-red
Middle Proterozoic gneissic granite. See fresh surfaces in a small
quarry visible on the west-facing hillside, before you reach the main
part of the community. Turn onto the quarry road, park just off the
highway, and walk the short distance into the quarry.
The shorelines in the community and at Saddle Island, where the
historic Basque whaling operation was located, are composed of dark grey
gabbro deformed during the Grenvillian Orogeny. An outcrop of this rock
forms the shore just east of the Visitor Centre. The gabbro is coarse
grained and contains grey feldspar crystals up to 3 cm in length, as
well as black pyroxene and biotite. It weathers to a lighter mottled
grey_white, and is slightly magnetic.
Slabs of Cambrian sandstone from farther west on the coast have
been used to pave the approach path to the Visitor Centre.
Labrador stops reached by coastal boat:
Stops 89 to 110 are reached by ship, using the Labrador coastal
service operated by Marine Atlantic. The larger communities also have
daily air service. Descriptions and directions for rock outcrops at
"wharf ports" are given from the perspective of the wharf at which the
ship docks. Some communities have no large wharf, and deliveries are
shuttled by local boats.
6. "Devil's Dining Table"
At Henley Harbour, to the right and up behind the
community is a very large, flat-topped rock feature known as "The
Devil's Dining Table". The top layer or cap rock is massive basalt.
Below it is an older, thicker basalt layer in which vertical cracks or
columns formed during cooling, looking like a multitude of "legs"
supporting the "dining table". This is called columnar basalt. Both
volcanic layers are flat lying, and were erupted on an ancient erosion
surface of red gneissic granite, the reddish rocks on the shore.
Eruption probably took place in Late Proterozoic time when the
continents broke apart to form the Iapetus Ocean (see Plate Tectonics
panel). The local name for the basalt hill is Castles Island.
7. Gneissic granite, Mary's Harbour
The rocks at Mary's Harbour are Middle
Proterozoic gneissic granite. There are flat, smooth outcrops on the
hill just behind the wharf, and fresh rock faces may be seen in roadcuts
on the land side of the road to the town.
The rock has alternating bands of pink, grey and black gneiss,
crossed by veins of coarse-grained, pink granite up to half a metre
wide. The gneiss bands are mostly straight or gently curved, but some
have been folded. The high pressure and temperature that affected these
rocks, 25 km below the Earth's surface, separated the minerals into dark
bands, rich in hornblende and biotite, and light bands which are mostly
white quartz and pink or white feldspar. Pink granite veins cut across
the gneissic bands and are therefore younger.
8. Deformed gneiss, St. Lewis (Fox Harbour)
St. Lewis lies at the southern
end of a 30-km-wide belt of strongly deformed gneiss, formed before the
Grenvillian Orogeny, when two parts of Labrador were squeezed past each
other along a fault. The rocks were crushed and weakened and in some
places weather out as small platy fragments. This can be seen in
outcrop faces to the right of the wharf, and on the land side of the
road toward the main community.
To the right of the old school building at the back of the bay
below the airstrip is a smooth outcrop of gneiss, in which eye-shaped,
pale pink, feldspar crystals are up to 1 cm across; this rock is called
"augen gneiss" after the German word for eyes. Much smaller black
biotite and white quartz grains wrap around the augen. This outcrop is
farther from the fault than the one at the wharf, and does not show the
same intense deformation.
As the ship leaves St. Lewis and rounds the next headland, you can
see that the rugged cliffs are weathered into vertical grooves and
columns. This feature is another result of the vertical lines of
weakness created by the major fault zone.
9. Mafic gneiss, Port Hope Simpson
The mafic (dark) gneiss at Port Hope
Simpson was formed by metamorphism of anorthosite and gabbro. There are
low roadcuts of this gneiss on the land side of the road that leads from
the wharf to the town, and up to the airstrip. The main minerals are
hornblende, biotite and feldspar, which occur in varying proportions,
giving the rock a banded appearance. A very small amount of pyrite is
also present; its weathering gives a rusty look to some of the
exposures.
The Alexis River valley, in which the town lies, results from
preferential erosion of a large anorthosite intrusion. The prominent
hill behind the town is a resistant knob of granite.
10. "Hole in the Wall"
Between Williams Harbour and Pinsent's Arm, an
interesting feature known as "Hole in the Wall" may be seen in the
landward cliffs. Erosion of weaker zones in the rock has created a hole
in the cliff face, which extends through to the valley beyond.
Vegetation in the valley wall can be seen through the hole as the ship
passes. The cliffs in this area are made of metamorphosed Middle
Proterozoic gabbro, 1650 million years old.
11. "American Men"
Along the coastal islands, particularly between Snug
Harbour and Black Tickle, the highest, most prominent hills are crowned
by stone markers or cairns. They are known on the coast as "American
Men", and are used as aids to navigation in bad weather. Many were
erected by native people and early European visitors and have existed
for hundreds of years. The term may be a corruption of "Marker Men".
12. Gneiss and gabbro, Black Tickle
The community of Black Tickle lies on the
contact between Early Proterozoic granite gneiss, distinguished by
large, pink feldspar crystals, and Middle Proterozoic dark, coarse-
grained gabbro intrusions. The name Black Tickle comes from the narrow
channel (or "tickle") flanked by dark-weathering gabbro that lies
immediately east of the community. The extensive outcrop area behind
the wharf is the light-coloured granite gneiss. If there is time, a
walk to the east end of the community allows you to see the gabbro.
This same resistant rock type forms most of the islands and headlands
between Black Tickle and Cartwright.
13. Gneiss and gabbro, Horse Chops Island
The cliff at the east end of Horse
Chops Island faces Packs Harbour, the next community north of
Cartwright. The cliff is composed of rusty weathering, massive gabbro,
above flat-lying gneiss. The gneiss on the shoreline was formed by
metamorphism of sedimentary rocks and appears as obliquely dipping
slabs.
Horse Chops Islands exist in local terminology at a number of
locations around Newfoundland and Labrador. While the name suggests
resemblance to a horse's head or mouth, the likeness is often tenuous.
From Cartwright to Packs Harbour the ship travels a long way out
around Huntingdon Island. This is because the broad bay between the
island and the coast is very shallow. The North River flows into the
bay, bringing large quantities of sand from inland, and makes navigation
treacherous.
14. Porcupine Strand, North Strand
Between Packs Harbour and the entrance to
Groswater Bay, a magnificent white sandy beach stretches for 35 km south
and north of Cape Porcupine. The normal track of the ship is 10 km
offshore from the southerly section (the Porcupine Strand), but less
than 5 km from the North Strand.
The beach sand is derived from sand and gravel deposited inland in
front of retreating glaciers about 10,000 years ago. Black sand beds in
the beach deposits consist of magnetite, ilmenite and other heavy
minerals concentrated by storm action. The black sand is being assessed
for possible commercial production of titanium and garnet. If quantity
and concentration are high enough, the valuable minerals could be
extracted by placer mining methods, and the remaining sand replaced.
15. Lake Melville rift valley from Lake Melville
The route along Lake
Melville follows a Late Proterozoic rift valley, created as a large
crack in the Earth's crust when the continents started to break apart to
form the Iapetus Ocean (see Plate Tectonics panel). The south side of
the valley is bounded by anorthosite and granite of the Mealy Mountains.
Part of the low-lying region on the northwestern shore of the lake is
underlain by sandstone and conglomerate, sediments that filled the
valley in Late Proterozoic time. Gently dipping red sedimentary rocks
of this unit can be seen from the ship on the western end of Green
Island, in the northeast part of the lake. The profile of the island
reflects its composition, being low and gentle, in contrast to the more
rugged granitic islands.
16. Grenville_Makkovik province boundary at Smokey
The group of islands at
Smokey straddles the boundary between the Grenville and Makkovik
structural provinces. Early Proterozoic gneiss and granite have been
intruded by Middle Proterozoic, black-weathering, folded gabbro dykes
that form distinct ridges or bands across many of the islands. These
dykes are the same age (1426 million years) as the gabbro north of Packs
Harbour (see Stop 16).
Segments of a large dyke crossing the southern end of Brig Harbour
Island can be seen in passing. Another large dyke crosses the northern
part of Brig Harbour Island almost parallel to the first. This dyke is
covered with vegetation, so that the darker colour cannot be seen, but
its edges are visible as linear depressions or ditches because the
gabbro weathers lower than the country rock.
A banded, fine-grained rock called mylonite, formed by grinding up
of the original rocks during fault movement, is exposed on the north
side of Cut Throat Island, where a major fault zone intersects the
coast. The fault marks the boundary between the two structural
provinces, and its expression is the line of cliffs seen on the north
side of the island.
17. "The Quaker Hat"
About two hours after leaving Smokey northbound, the
ship passes an isolated island shaped like a broad-brimmed Quaker hat,
complete with a black band around the base of the crown. The band is a
sill of gabbro, which intrudes the rest of the "hat", composed of Early
Proterozoic granitic rocks. When the ship's horn sounds, clouds of
birds (mainly turrs, a Newfoundland term for murres) rise into the air.
18. Cape Harrison granite
Cape Harrison is a prominent headland composed of
red, Early Proterozoic granite, mixed with older rocks. The vertical
columnar effect on the face is a result of strong vertical jointing that
formed during the time the rock was cooling from a liquid magma.
Glaciers moving over the surface more than 10,000 years ago plucked out
rock fragments bounded by the joint planes. Frost and water action have
continued the job from that time to the present.
102. Weathered syenite, Ragged Islands
The ship passes inside the Ragged
Islands about an hour after passing Cape Harrison. On the south end of
the westernmost island, apparent sandbanks are the gravelly weathering
product of syenite, an intrusive igneous rock. This variety is known as
"Rapakivi", a Finnish word for "rotten rock". It is surprising to find
sand out in this harsh and dynamic environment. Apparently the rock is
weathering rapidly enough to replenish the quantities removed by wind
and waves.
19. Granite, Benedict Mountains
The Benedict Mountains, visible to the
southwest from the ship, are composed of Early Proterozoic granitic
rocks of the Trans-Labrador batholith, which intruded into older
intrusive and volcanic igneous rocks of the Makkovik Province. This
rugged, resistant barrier, greater than 50 km in length, reaches a
maximum height of 700 m.
20. Rhyolite, Makkovik
Metamorphosed rhyolite that is 1860 million years old
outcrops around the community. These rocks were probably erupted in a
volcanic island-arc similar to those around the rim of today's Pacific
Ocean (see Plate Tectonics panel). The island-arc would have been near
the margin of an Early Proterozoic ocean, which then closed to form the
Makkovik Province.
The rhyolite weathers white, while a fresh surface shows it to be
pale grey and sugary in texture, with fine black specks of magnetite
throughout. Narrow, dark green gabbro dykes intruded the rhyolite and
are usually near vertical. The best exposure close to the wharf is
behind the large fuel tanks directly above the wharf. A gabbro dyke
crosses this outcrop on the left.
The rock surface has been smoothed by glacier ice, and there are
several sets of striations, indicating that the glacier moved
northeasterly, toward the sea.
The high hill topped by a transmission tower that you can see to
the southwest when approaching Makkovik is called Monkey Hill. It
consists of granite of the Trans-Labrador batholith intruded into the
rhyolite, after the latter was deformed during the Hudsonian Orogeny.
21. Gneiss, Postville
Postville is built on Archean gneiss that was
intensely deformed and ground up (mylonitized) during the Early
Proterozoic. Good examples of mylonitic gneiss can be seen behind the
airstrip building, and in a rock quarry beside the road leading to the
airstrip. The airstrip is straight up the hill behind the wharf, about
1 km away. The gneiss is fine grained and intricately folded, with
flattened knots of buff-coloured feldspar, and bands of white quartz and
black mica. Surfaces where movement has taken place are coated with
pale green epidote or dark green chlorite. A smaller outcrop of the
same gneiss lies along the road to the right of the wharf where a small
cliff has been blasted to make way for the road.
The high ridge seen to the northwest of the community, and Post
Hill directly across Kaipokok Bay, consist of metamorphosed basalt
erupted on the ocean floor during Early Proterozoic time.
22. Granite and gabbro, Striped Island
About halfway between Postville and
Hopedale, the ship passes inside Striped Island, which is composed of
pale, buff-weathering granite with nearly horizontal joints. Dark green
to black gabbro sills have been intruded along the joints and the
resulting effect is prominent horizontal stripes. The gabbro "stripes"
have weathered more rapidly than the granite ones, and appear indented
in the surface. The stripes are best seen on the south side of the
island.
23. Archean gneiss, Hopedale
The barren promontory on which Hopedale stands
consists of Archean gneiss about 3000 million years old. These rocks,
which belong to the Nain Province, formed part of the ancient continent
upon which sedimentary and volcanic rocks of the Makkovik Province to
the south were deposited. The gneiss is vividly banded in black
(biotite-rich) and white (feldspar- and quartz-rich), and is cut by
veins of pink granite produced by melting of the rock during
metamorphism. The banding is almost vertical and can be seen in many
cliff faces. Early Proterozoic diabase dykes form conspicuous, nearly
vertical, black sheets that cut across the banding on many of the
islands around Hopedale.
The contorted gneissic banding and granite veins are best seen on
smooth shoreline exposures between the "American Dock", where the ship
lands and which was built when this was a US radar base, and the
community itself. Some of the best exposures are on the landward side
of the new shore road.
24. Archean gneiss, Windy Tickle
About two hours after leaving Hopedale, the
ship passes through a narrow, deep passage, 4 km long, called Windy
Tickle. On the west or landward side of the passage, 200-m-high cliffs
of pink Archean gneiss tower over the ship. The straight passage
produces a wind tunnel effect with certain wind directions.
Close to the south end of the tickle, a dip in the cliff wall
suggests that glaciers carved out a cirque or hanging valley up above.
109. Archean gneiss, Davis Inlet
The bedrock in the community of Davis Inlet
and the islands just to the east is Archean gneiss. Toward the south
end of town, on the roadway, is a smooth, weathered knob of this gneiss,
which contains feldspar, quartz, pyroxene, hornblende and biotite. The
town itself is mostly built on glacial sand and gravel. The high hill
behind the town is anorthosite, which was intruded into the gneiss
during the Middle Proterozoic and is part of the Nain anorthosite (see
Stop 110).
25. Nain anorthosite
The hills surrounding Nain are composed of coarsely
crystalline, grey anorthosite, a resistant rock that intruded Archean
gneisses in this part of Labrador in Middle Proterozoic time (1300
million years ago). Anorthosite is made of feldspar and small amounts
of pyroxene. Locally, traces of pyrite make the weathered surface look
rusty.
Weathered anorthosite forms the hills behind the town, but the
best place to see a fresh exposure is to the northeast, beyond the end
of the airstrip. Here, in a quarry, veins of pink granite intrude the
anorthosite.
The type of feldspar in anorthosite is labradorite, a semiprecious
stone which is the official mineral of the province. Labradorite can
exhibit iridescence, a brightly coloured internal reflection (blue,
green, yellow, bronze), best seen by rotating a wet piece of crystal
until one of the surfaces catches the light. Labradorite used for
jewellery work comes from coarse crystalline pods or lenses, with
crystals ranging in size from several centimetres to over a metre. Such
pods are present throughout the Nain area. It is possible to find small
glimpses of "colours" in the quarry at Nain.
This series of web pages provides an introduction to the publication
below, which can be ordered from the
Geological Association of
Canada 
Newfoundland and Labrador Traveller's Guide to the Geology
Edited by: S. Colman-Sadd and S.A. Scott, 91 pp. + map, 1994
Northern Peninsula- southern Labrador |
Trans-Labrador Highway|
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