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C


PART XV.


DOCUMENTS DESCRIPTIVE OF TOPOGRAPHY OF THE COAST OF LABRADOR AND OF CONDITIONS IN GENERAL ON THE COAST



No. 1036.

TOPOGRAPHY OF THE NORTHEAST COAST OF LABRADOR.

BY REGINALD A. DALY, S.D., F.R.S.E., CHAIRMAN OF THE DEPARTMENT OF GEOLOGY AND GEOGRAPHY, HARVARD UNIVERSITY.

To understand the topography of the Labrador coast, one may well take a preliminary glance at the geological history of the region.

GENERAL SKETCH OF THE GEOLOGY.

From Belle Isle Strait to Ungava Bay the island belt and mainland of Labrador are almost entirely composed of very ancient rock-formations. These formations are typical of the Basement Complex of the North American continent. While some of them have the features of the so-called Huronian Series of rocks, the larger part of the coast-belt appears to be still older and to be “Archean.”
Characteristic of such old, pre-Cambrian rocks throughout the world, is their mountain-structure. So it is along the whole northeast coast of Labrador. Long ago, namely in later pre-Cambrian time, the rocks of Labrador were everywhere folded, broken, jammed together, in a way quite similar to that illustrated in the cores of any of the much younger mountain chains, like the Alps or the Coast Range of British Columbia.
After these enormous, very ancient disturbances of the Labrador formations came to an end, the peninsula was much more rugged than at present ; its steep topography was analogous to that of the Alps, but the deformation was not confined to a relatively narrow belt, like the Alps. On the contrary, the very rugged mountainous relief of this pre-Cambrian era seems to have stretched continuously from the line of the present coast all across the Labrador peninsula into Quebec and beyond.

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Because this old, mountain-land was high, it was subjected to erosion or denudation. The processes of erosion were slow, but sure, so that, already in late pre-Cambrian time, the mountainous relief was worn down close to sea-level. The rugged topography finally evolved into that of a low-lying, almost plain surface. Such a surface is called, technically, a peneplain. It is probable that a few residuals of rock-masses, specially slow to yield before the attack of weathering and erosive agencies, long remained above the general levels of the peneplain surface. Yet, in general, mountain-form (great height and ruggedness) was largely lost throughout Labrador. The worn-down roots of the ancient complex remain to this day. Everywhere the dominant Labrador rocks have preserved their mountain-structure.
Along the northeast coast there is only one limited area where the preceding description needs modification. This area occurs at and near Cape Mugford. Here the dominant basement complex of rocks, after its profound erosion, was buried under a thick mass of volcanic rocks and associated strata which were laid down, in a nearly horizontal position on the old surface of erosion. This younger formation is called the Mugford Series of rocks. These have been deformed only to a moderate degree; hence, over an area of 200 or 300 square miles, around Cape Mugford the structure and relief of the coastal belt differs markedly from all the rest of the belt from Belle Isle to Cape Chidley.
Long after the Labrador peneplain was formed, the whole peninsula, including the northeast coast, was warped. Extensive areas were uplifted so as locally to reach heights of a mile or more above sea-level. Other extensive areas were warped down below sea-level.
Areas of specially strong uplift include the highlands called the Mealy Mountains (south of Hamilton Inlet) ; the Kiglapait block (between Nain and Cape Mugford) ; the Kaumajet Mountains (at and in the vicinity of Cape Mugford); and the Torngat Mountains, the highest of all. (The Torngats stretch from near Hebron to Cape Chidley).
Areas of strong downwarp or subsidence are represented by Ungava Bay and by the submerged, coastal shelf which extends from Belle Isle to Ungava Bay. In these two extensive areas the ancient peneplain is completely drowned, out of sight under the Atlantic water.
The uplifted parts of the old-mountain peneplain were immediately attacked by the erosive agents. The chief agent was running water. The rivers began to cut gorges and canyons in the new highlands.
Then came the Glacial period. With the exception of a few of the highest peaks in the uplifted land north of Cape Mugford, the whole of the Labrador was covered by an ice-cap, comparable with the Antarctic ice-cap of the present day. This Labrador glacier slowly scoured away the soil and quarried away much rock from the solid ledges of the peninsula. Such glacial erosion was most pronounced in the river canyons which had already been cut on the Torgat and Mugford uplifts, but everywhere the Labrador topography was changed in quality by this glacial attack. The huge ice-sheet worked differentially; here quickly scouring out rock-basins—there smoothing hills

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which it could not destroy. In this way the well-graded peneplain was trans-formed into a maze of rounded hills and hollows. The topography of Labrador in general had become hummocky. Since the ice-cap went out to sea and scoured and quarried the sea-floor also (where less than 100 fathoms or so in depth), the hummocky topography was developed far out on the submerged shelf all along the coast.
Both before and after the Glacial period, the Atlantic waves have cut into exposed headlands. Hence at many points the coast is “ steep-to ” with sea-cliffs reaching 100 feet to 2,000 feet in height.
Finally, it should be noted that the Labrador peninsula as a whole was temporarily depressed during the Glacial period—simply by the great weight of the ice. After the ice-cap melted away, the earth's crust did not immediately respond and rise to its pre-Glacial level. Hence for a considerable time the Atlantic water transgressed upon the coast. During this late-Glacial and post-Glacial submergence of the northeast coast, the ocean waves built hundreds of short beaches in the bays and among the islands of the coastal fringe. These beaches have recently been elevated, because the earth's crust ultimately responded to the removal of the ice-load. These elevated beaches are found at heights of from 250 feet to 400 feet above present sea-level.
The elevated beaches and those now forming represent practically the only loose material on the Labrador coast. Everywhere else along the shores of islands and mainland, hard, solid bed-rock forms the surface and that surface is characteristically strongly sloping or hummocky. There is good reason, therefore, for the common rule along the coast, that settlements and cemeteries are located on elevated beaches. The almost universal absence of a true soil along the shore is also largely explained by the severe washing of the shore-belt during the recent submergence.

TOPOGRAPHIC UNITS TRANSVERSED BY THE NORTHEAST COAST

1. Throughout the southern half of the northeast coast, that is, from Belle Isle Strait to Ford Harbor, near Wain Mission Station, the general shape of the country is determined by the seaward downwarping of the old-mountain peneplain. The downwarping of its ice-scoured surface was gentle, so that there is a more or less persistent fringe of low islands along this half of the coast. These islands are simply the hummocky hills of the peneplain where this great surface was drowned under the Atlantic water. The islands here range in height from a few feet to about 600 feet. The average height of the islands rises slowly from the side of the open ocean toward the mainland.
The mainland itself has the same hummocky quality, and its average surface level rises slowly toward the interior of the peninsula. The water divide is 20 to 100 or more miles inland from the shore of the mainland. The position of the divide or “ height of land ” is fixed by irregularities in the warping of the old-mountain plain, as well as by the differing amounts of glacial. erosion on the peninsula. Neither of these conditions affords any clear-

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cut separation of a coast-belt from the main body of the Labrador peninsula. Though the old mountain structure tends to parallel the northeast coast, there is no well-defined mountain range along the coast in the region south of Nain. Occasionally, hills, somewhat higher than the average, do interrupt the coastal profiles, but they are isolated and not parts of a continuous, northwest, southeast chain.

HIGH MOUNTAIN BLOCK FROM NAIN TO MOUNT THORESBY (PORT MANNERS).

2. A little south of Nain, a large mass of massive, strong rock crops out in bold, steep mountains which rise directly out of the ocean water to heights of 600 to 1,500 or more feet. This bold topography may be due partly to specially great upwarping of the old-mountain peneplain, but probably the high relief is due to the nature of the rock—technically called a gabbro.
This rock covers an area, probably 40 miles long, as measured along the coast, and extending far into the interior of country. The seaward edge of this massif of “ Nain gabbro ” is cut by steep-walled, fiord-like valleys, some of which have been so drowned as to form through-going channels, the seaward mountains of gabbro constituting high islands with steep-to shores on all sides.

THE KIGLAPAIT MOUNTAIN RANGE.

3. Immediately north of the Nain gabbro mountains is a short, but rather spectacular range running east and west along the mainland shore. This range, called the Kiglapait by the Eskimos, has never been explored, but photographs, from the sea, show that this local, east-west range rises directly from salt water. The individual peaks appear to have heights varying from 2,000 to 2,500 feet.

KAUMAJET MOUNTAINS.

4. From the bay just north of the Kiglapait nearly to Mugford Tickle, a distance of about 30 miles, the topography is not so bold and there are a number of islands which form a fringe, analogous to the island fringe from Nain to Belle Isle Strait. However, these islands are on the average higher, some reaching 1,000 feet or so in altitude. In fact, the coast-belt all the way from Nain to Cape Chidley, may be described as high, rugged, and steep-to on its seaward side.
At and around Cape Mugford we have the remarkable and quite special topography, due to the presence of the Mugford series of rocks, above described. The relatively flat position of these beds of rock causes the sea cliffs to be here very steep. Because the bedded series is thick, the cliffs are lofty, ranging from 1,000 feet to 2,000 feet or more in height above the sea. Those elevations characterize both the mainland portion of the Kaumajet Mountains and the large island of Ogualik, which appears to be a seaward continuation of the Kaumajet Mountain group.

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5. The remaining element in the coastal topography is the Torngat Range, which becomes individualized only a short distance north of the Kaumajet Mountain group. The Torngats represent a belt of the old-mountain peneplain, where upwarped higher than anywhere else in the Labrador peninsula. This belt of the earth's crust was hoisted up 3,000 to about 5,000 feet, either by arching or by tilting. Since then rivers and local glaciers have cut deep canyon-like valleys and true fiord valleys, the relief finally becoming much like that of western Norway, except that the Torngats are not fringed with a low coastal flat and series of low islands, as is the case with the Norwegian Mountain system.
Almost everywhere the Torngat Mountains descend abruptly into the salt water of the fiords or of the open ocean.

SUMMARY OF THE GENERAL TOPOGRAPHY OF THE NORTHEAST COAST BELT

It thus appears that the four principal topographic units of the northeast coast, north of the latitude of Nain, together represent an almost continuous mountain land. This high ground bears a water divide situated from 10 to 75 miles from the northeast coast, and probably everywhere not far from half-way between this coast and George River. With the exception of a few bay-heads and a few islands, the shore does not permit of settlement, for any purpose, the sea-cliffs and mountain slopes rising elsewhere steeply out of salt water.
Taken as a whole, the Nain-Kiglapait-Kaumajet-Torngat Mountain group is a distinct entity, a distinct topographic province of the Labrador peninsula. To seaward this province is sharply bounded directly by the Atlantic shore-line. On the west the province fades into the general, lower, more plateau-like interior of the Labrador peninsula.
Evidently this mountain land is of no value to the fishing industry except as it supplies a few harbours and sites for fishing stages in fiords and other bays. The contrast with the coast-belt south of Nain, with respect to the abundance of safe harbours, is striking. Thus, between Saeglek Bay and Nachvak Bay, the only safe anchorage is at Ramah. The climate is against the use of the rare shore flats, for the purpose of drying fish successfully. In the almost complete absence of tree growth, fire-wood and other timber, useful to fishermen, are practically non-existent in this half of the northeast coast. It is safe to assume that, in the pursuit of his business, any fisherman would not need to penetrate inland more than a few hundred of yards at any point on this part of the coast.
South of Nain, throughout the southerly half of the northeast coast, and around to Blanc Sablon, there is no similar separation of the coast belt from the rest of the Labrador peninsula.
Here the old-mountain hummocky peneplain rises rather gently to the general plateau level of the Labrador peninsula. There is a height of land or water-divide far to the westward, but this divide is not that typical of a mountain range. It has been determined chiefly by an almost insensible

[1927lab]



 

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