Drive out of Stephenville on Route 490 heading for Stephenville Crossing. Pass by the Abitibi-Price newsprint plant, and as you begin to climb the hill, watch for an old fuel storage tank and woods-road on the left hand side. They are just past the first outcrop on the left. The woods-road has been blocked off, but there is room to park and then walk up the left side of the highway.
The nearest part of the outcrop is mafic gneiss, dark and rusty, and lighter diorite bands, mostly running parallel to the face. Within the mafic gneiss are veins and a horizontal lens of black magnetite. Magnetite from this area was used as a source of iron during World War II, and about 16,000 tons were mined. The mafic gneiss contains a lot of magnetite in addition to feldspar, pyroxene and hornblende; the diorite contains more feldspar, less pyroxene, some quartz and a little magnetite. All of the rocks are fractured and jointed because of their brittle nature.
Farther uphill, a large mass of pink/green granite gneiss underlies the mafic gneiss. The granite gneiss is composed of quartz, pink and white feldspar, black pyroxene and hornblende. Mineral banding, the main characteristic of a gneiss, results from separation of the different minerals under extreme heat and pressure during metamorphism. Cracks contain pistachio green epidote, an alteration mineral.
When you turn to admire the view back across the plain to Stephenville, note in the distance the bluff of delta gravel and sand, on which the community of Kippens is built. The line of houses marks the level top of the delta, and indicates the height of the sea when the glaciers receded from this area, 12,000 to 14,000 years ago. In the middle distance is the modern barachois bar built by wave action after the postglacial river cut through the delta.
The quarry is on the road between Aguathuna and Boswarlos. The best place to see the unconformity is in the east half of the quarry wall. About 20 m of the older creamy-buff dolostone can be seen; the upper part is more laminated than the lower, and the beds are thinner. It is mottled with worm burrows (tube-like structures), and contains stromatolites (fossil algae, which appear as finely laminated, low mounds up to 1 m high), especially near the top in the centre portion. The top has been eroded before deposition of the younger limestone, and beds are cut off against the unconformity.
The overlying grey, Middle Ordovician limestones, like the older beds, are dipping toward you at about 10. As you move along the quarry face, you will see that there is a hollow eroded in the older surface, and it is filled with the upper, younger limestone. This is best seen by looking along the face from one side. This kind of irregularity is characteristic of any erosion surface, including the surface of the land today.
During quarrying operations, the "island" of fossil-bearing limestone in the centre of the quarry floor was left untouched. It is a piece of much younger Carboniferous limestone that was undesirable because it contains pyrite, galena, barite and celestite. It filled a Carboniferous sinkhole formed when groundwater dissolved Ordovician rocks along a fault.
A path leads down to the beach from the Ultramar gas station at Piccadilly. At the beach, turn right and you will see that the flysch unit above, consisting mainly of black shale, has been completely fragmented where it overlies the limestone along a thrust fault. Folds are lying on their sides and many of the beds have been overturned. The limestone below has been fractured, but not as much as the flysch, suggesting that the flysch was detached, folded and crushed against the limestone by the movement of the overlying allochthon.
Across the road from the gas station and 100 m west is a small quarry in the same
limestone. The thin bedded parts contain fossil graptolites and small clam-like ostracods for
collecting.
To see the limestone, drive past Lourdes toward Black Duck Brook. Continue 1.5 km beyond the right angled turn where the road reaches the east side of the peninsula, to an intersection with a paved road leading west to part of the community. Park near the intersection and walk 100 m along a track to the right, between two fences, to the eastern cliff top. Follow the steep path down to the beach.
The cliffs are about 15 m high. The beds of fossil-bearing limestone are overlain by pinkish sandy mudstone separated by thin layers of softer grey-green shale. A few isolated coral reefs may be seen, as well as beds of fossil debris. Usually the coral occurs as circular or wall-like masses, and would have stood perhaps 1 m above the ancient sea floor. As you emerge onto the beach, you may notice the weathered base of a reef on a limestone slab that sticks out of the beach.
These coral reefs are about 450 million years old, but are remarkably similar to modern coral reefs around Bermuda.
The mouth of the Humber Gorge is out of sight around to the right beyond the city, but to the left of it Wild Cove valley is visible. Glacier ice probably flowed down this valley and out into Humber Arm; note the flat bottom and U-shape characteristic of glaciated valleys. On the north side of the arm west of Wild Cove are remnants of gravel terraces up to 50 m above the water. These were formed about 12,500 years ago, where sediment-filled rivers from melting ice entered the sea. At that time the land was still depressed by the weight of the ice, so the level of the sea was higher than it is today.
Gravel terraces are attractive places for people to build houses: level ground, good digging for basements and foundations, well drained, and good gardening. Throughout the area, many houses are built on these ancient terraces and river deltas. They also represent important sources of gravel for use in concrete and road construction.
To reach Bottle Cove, take Route 450 from Corner Brook almost to Lark Harbour, take the left turn for Little Port, and turn right onto the Bottle Cove Lookout road. The road circles the cove and climbs to a parking lot, from which a trail leads to the north head. You can walk either way around the cove, climb on the headlands, and enjoy the view.
Out on the headlands are dark green and dark red basalt pillow lavas, consisting of rounded, bulbous masses thought to have been extruded under water. The hot molten lava cooled quickly when it encountered the cold water, resulting in these curious shapes. You can see them best in the steep cliff below the turf at the end of the path; on the outer side, rounded pillows have weathered out of the cliff and form a small bouldery beach.
Return to the lookout entrance and turn right. At the end of the road is Little Port, a tiny fishing harbour, where more of the allochthon is exposed. The walls of the harbour are best examined at low tide. On the far wall is mélange, a grey-black scaly shale containing blocks and fragments of volcanic and ophiolitic rock. To its left is undisturbed shale containing fossil graptolites. Above the mélange, farther out on the south wall, is a conglomerate of boulders of volcanic and intrusive rock, overlain by sandstone. The conglomerate and sandstone are also part of the Humber Arm Allochthon. The near wall consists of pillow lava that is actually a large block in the mé lange.
Evidence of the later drainage can be seen in the gorge. As you drive through, observe the smooth, pink- and cream-coloured marble wall beside the highway just downstream from the ski resort. There are no striations or grooves such as ice would make, only the smoothly undulating, water-worn surface. While we have the highway construction to thank for exposure of the smooth marble walls, the same excavation has also removed access to the marine shell deposits higher up.
Since the 1880s, marble in this area has been quarried intermittently for building stone, and in the past some was crushed for use in Corner Brook in the paper-making process. Small quarries or "rooms" are visible high above the road, just downstream from the smooth walls. There are plenty of samples of the different coloured of marbles on the slope.
Stop on the shoulder of the highway between the Deer Lake power plant and the turnoff to Spillway and look north toward the community of Nicholsville. You can see at least three wave-cut terraces above the present beach level.
As you start to descend the long hill from the lookout point, the rocks are pink and green Middle Proterozoic gneiss cut by pink granite veins (see diagram). These rocks were formed by metamorphism and igneous intrusion during the Grenvillian Orogeny about 1000 million years ago.
Part way down, where there are roadcuts on both sides, you pass through the unconformity, through a very thin layer of basal pebble conglomerate (pebbles are from underlying Middle Proterozoic gneiss and granite) and into Early Cambrian purplish-grey sandstone. The sandstone is slightly magnetic because it contains many fine grains of black magnetite. The beds dip more steeply than the hill slope, so as you descend, the rocks are getting younger. With your last few steps you have travelled 500 million years in time! Above the purplish-grey sandstone is more Early Cambrian sandstone, but this time dark green-grey in colour.
Next up in sequence, and the youngest rock type in the exposure, is Early Cambrian fossil-bearing limestone alternating with thin dark shale layers. These rocks were deposited in a continental shelf environment and as sea level changed, limestone deposition alternated with mud deposition.
This terrain has a strange appearance because of its yellow-orange colour and its unusual vegetation. Ultramafic rocks are rich in elements that inhibit plant growth, and so vegetation is extremely sparse, especially compared to the hills on the north side of the highway. The plants that do grow on these rocks are specially adapted to this particular environment. For more information, see the Parks Canada exhibit just off the highway at the east end of The Tablelands.
The community of Trout River is built on sand and gravel that was deposited on a delta by glacial meltwater. The delta formed when a glacier melted and receded up what is now Trout River Pond, about 12,000 years ago (see Glacier panel). The pond itself is a fiord, landlocked by the rebound of the land surface after the weight of the ice sheets was removed. Evidence of the delta may be seen by standing near the mouth of the river, and looking to the north across the small bay. The upper half of the community is built on the flat top of a younger delta surface (elevation 35 m above present sea level), while above that, remnants of an older delta surface at an elevation of 70 m can be seen. In each case, Trout River has cut its way through the sediments so that it can flow out to the sea.
Get a better view of the delta by taking the trail to the Old Man Lookout and Pond View. The trail begins on the south side of the river, across the bridge in the community. The Old Man is a stack, eroded by the sea when the land level was lower. The Pond View Lookout is reached by continuing on the trail about 2 km farther to the east, to where you can look straight up the pond, with the barren Tablelands on your left.
Reasons for the instability are thought to include oversteepening of the slope by glacial erosion, loss of support by the ice mass (after the glacier melted), and weaker sedimentary rocks at depth below the stronger igneous rocks on surface.
The rocks that form the impressive walls of Western Brook Pond are made of Middle Proterozoic granitic gneiss, which was metamorphosed during the Grenvillian Orogeny about 1000 million years ago. If you take the boat tour along the pond, you will notice that the rocks in the cliff walls have vertical cracks, which have been intruded by dark green diabase dykes up to 10 m wide. The cracking occurred about 600 million years ago, as the ancient continent broke apart to form a new ocean called Iapetus (see Plate Tectonics panel).
More information about Western Brook Pond can be found in a display at the Gros Morne Park Visitor Centre, south of Rocky Harbour.
The Cambrian and Ordovician conglomerate is thought to have formed in deep water on the continental slope of the Iapetus Ocean. As the slope steepened, earthquakes may have created underwater landslides in which the partly consolidated limestone broke free and rolled down the slope, forming the chaotic mixture visible today.
To see the Cow Head conglomerate, drive across the causeway out to the peninsula in Cow Head, park by the wharf, and continue to walk along a short lane to the north shore. The entire peninsula consists of the same formation, but the best exposure is along the north shore and on the western beach. The small point ahead of you is a good place to view the conglomerate. Other parts of the formation are exposed in the cliffs along the beach and, by walking along the beach, you can see a continuous section. Small faults cross the layers at intervals, dragging them out of line.
If you choose to continue along the beach, which is a good walk, be advised that there are only two paths up the cliffs and through the tuckamore spruce before reaching the vicinity of the old lighthouse, so you will want to watch for them. The paths lead to the lighthouse itself, where there is a good view; then you can return to the wharf by the old road.
Here and elsewhere in the area are plenty of examples of the grey Ordovician dolostone that hosted the zinc mineralization. The dolostone is shot through with white carbonate veins, and you may find a sample of the sphalerite (zinc sulphide) which was mined here. Sphalerite is a resinous, non-metallic mineral, which varies in colour from dull yellow through brown to black, when it is called "blackjack". A piece of rock containing an appreciable amount of sphalerite feels much heavier than a similar piece of dolostone and, if you scratch sphalerite with a knife, it gives off a slight smell of rotten eggs.
Most of the open pits were located northeast of the millsite, while the restored tailings area is off to the south, a few hundred metres away.
Newfoundland and Labrador Traveller's Guide to the Geology
Edited by: S. Colman-Sadd and S.A. Scott, 91 pp. + map, 1994