EXTRACTS FROM REPORT ON “ GEOGRAPHY AND GEOLOGY OF LAKE MELVILLE DISTRICT, LABRADOR PENINSULA.”
BY DR. E. M. KINDLE, OF THE GEOLOGICAL SURVEY OF CANADA.
(Ottawa, 1924 : Memoir 141, No. 120, Geol. Ser.)
The great peninsula which lies between Hudson bay and the Atlantic ocean has long been known as Labrador peninsula. The name Labrador, signifying as it does in this connexion one of the great natural physical divisions of the continent, has a definite meaning. The precise significance of the name as used in this way is in sharp contrast with the vague meaning which attaches to “ the coast of Labrador ” as the name of a political sub-division of the Labrador peninsula subject to the authority of Newfoundland. No agreement has ever been reached between the Canadian and Newfoundland governments regarding the western boundary of Newfoundland Labrador. Some maps showing this western boundary of “ the coast of Labrador,” as claimed by Newfoundland,¹ place it in the Hamilton River basin about 350 miles west of the boundary claimed by Canada² in Hamilton inlet.
Among geographers the impression has been rather general that only the eastern seashore of Labrador peninsula is under the jurisdiction of Newfoundland, and the region to the west of it under the control of Canada. It is, therefore, a matter of considerable importance and some complexity to ascertain precisely how far inland the seashore extends along the waterways known as Hamilton inlet, The Narrows, and Lake Melville. Careful attention was given during the progress of the field work to the biological and geological data which appear to have a bearing on this problem, both on account of their application to a question of political geography and their general scientific interest. The highly interesting biological problems of distribution, which every river with a gradually expanding estuary presents in the modification of the marine and terrestrial forms of life associated with it as the transition is made from typical marine to brackish and freshwater conditions, are found here. But they are modified and complicated by the interpolation of a large lake between the sea and the drainage system of a considerable part of eastern
¹ Century “ Atlas of the World.” Edition of 1899, No. 59.
² Rand McNally Co.’s “ Indexed Atlas of the World,” vol. II, p. 317. The boundary shown on this map is assumed to be only approximately the same as that claimed by Canada.
Labrador. As a result of this unusual feature of the drainage the region is a peculiarly inviting one in which to study the influence of salinity in controlling the distribution of plants and animals and even the indigenous human races of the region the—Indian and Eskimo.
During the field work the writer traversed the north and south shores of Lake Melville. The Backway and Double Mer were traversed, and some of the streams entering Lake Melville ascended to the head of canoe navigation. Hamilton river was ascended to Muskrat falls. The entire length of Grand lake was traversed, and Naskaupi river, which enters this lake near its head, was ascended to the junction with the Red. A short canoe trip was made up the latter stream. The general geographic relations of the region examined are indicated on Figure 1. The areal relations of the formations recognized in the course of the writer’s work, and the earlier work of Low in the interior and Packard on the coast are shown on Figure 4.
Numerous soundings and hydrometer readings were taken, and dredging was done at a number of points.
A list of plants collected by Mr. R. H. Wetmore, botanist of the expedition, representing the flora of the district, is included in this paper.
Lakes and Sea-Connected Valleys.—The interior of Labrador peninsula “ is covered with myriads of lakes that occupy at a moderate estimate at least one-quarter of the total area.”s¹ Nearly all these are shallow lakes, the product of glacial damming, or rock basins. A few, however, are more than 400 feet deep, like lake Winikapau, an expansion of Hamilton river, 100 miles west of lake Melville. Small lakes are numerous in Lake Melville region ; nearly every brook flows into or out of one.
The very deep, fiord-like lakes connected with or near Hamilton inlet constitute one of the most prominent geographical features (Plate I and Figure 4). There are four of these deep waterways known respectively as Grand lake, lake Melville, The Backway, and Double Mer (Figure 4). All the rivers and streams of the region flow through or empty into these deep, narrow waterways. Grand lake, which is entirely fresh, has a depth of 90 fathoms, and a length of about 40 miles. Lake Melville, into which Grand lake empties, is a tidal lake and shows a maximum depth of 160 fathoms. The Backway, at least 80 fathoms deep, is a narrow arm connected with the eastern end of lake Melville. Double Mer approaches more closely than the others the fiord type (See Plate I), but the maximum depth found is only 46 fathoms.
The great depth of lake Melville allies it on the one hand with the fiords of Norway and on the other with the deep inland lakes and rivers of Quebec. The lake extends nearly 1,000 feet below sea-level and with its steep mountain
¹ Low, A.P., “ Report on Explorations in the Labrador Peninsula along the East Nain, Koksoak Hamilton, Manicuagan, and Portions of Other Rivers,” Geol. Surv., Can., Ann. Rept., vol. 8, p. 23 L, 1895.
The drainage system of this region, as it existed at the close of the Tertiary period, was the result of subaerial erosion directed or controlled by the structural features of the district. Nearly all the bolder and more fundamental features of the present drainage system probably developed during the Tertiary period. The old valleys of Tertiary date were, however, profoundly modified by the work of the ice during the Glacial period and by marine deposits still later. Re-elevation has given, as the product of this complex threefold ancestry, the present drainage system.
The valley of the Hamilton and its wide expansion, lake Melville, is the dominant or trunk valley of the region. The valleys that join the northwest and southwest sides of this great valley are of surprisingly contrasted types. On the northwest side occur wide, mature valleys like Grand Lake-Naskaupi valley, whereas the hanging valley descending the steep slopes by a series of cascades is the common type on the southeast side. The Kenamu, the largest southern tributary, enters Hamilton valley through a deep gorge. Double Mer, the only large valley outletting to the sea independently of the Hamilton system, duplicates in a smaller way on its northern and southern sides the contrasted types of valley shown by the two sides of lake Melville. Its streams, however, except the one at its head, are of rather insignificant size.
The explanation of these and some other features of the drainage is to be found in structural features of Pre-Tertiary origin. The steep, scarp-like, northwest face of Mealy Mountain highland and the equally steep mountain face which borders much of the south side of Double Mer are considered to be fault scarps which are probably of Pre-Tertiary age. The lowlands cut in the sandstone which floors the north sides of both of these valleys are terminated on the north by abruptly rising mountains of Precambrian rocks. The contact between these Precambrian mountains and the sandstone in both cases is believed to be a fault-plane. The wider parts of both Double Mer and Lake Melville basins are believed to be defined by fault-planes which have dropped down two large blocks (See Figure 5 A and C). On the relatively soft Palæozoic beds of these younger rocks have been cut the Double Mer and Lake Melville lowlands which are considered to be limited in part at least by fault-planes, as indicated in Figure 5 A and C. The effect of the downfaulting of these blocks was to bring in contact two strongly contrasted types of rock—the Double Mer sandstone and the Precambrian schists. Differential erosion in Tertiary and earlier times developed on these sandstones and other super posed and probably softer beds now entirely vanished, the relatively wide valleys which came in late Quaternary times to be occupied by lake Melville and Double Mer waterways.
In the bed of lake Melville the soundings made by the hydrographic engineers show clearly the location of three distinct valleys which occupied the broad western half of this basin in Preglacial time. Two of the three depressions representing them (Figure 5 A) can be followed by the soundings to the mouths of Mulligan and Sebaskachu rivers. The third, which
is near the south side of the lake, corresponds to the original valley of Hamilton river. These three old Preglacial valleys which the lake soundings disclose in the widest part of the lake draw together in a seaward direction after the usual style of river valleys, and where the lake grows narrower, east of Long point, unite into a single valley a few miles west of St. John island. This represents the old Preglacial trunk stream of Hamilton river. A cross-section of this part of the lake is shown in Figure 5 B.
The three valleys recognizable in the soundings of lake Melville referred to above may be more precisely described as modified Preglacial valleys. Details of these valleys have been changed by lake deposits since, and by ice erosion before, the departure of the glacial ice-cap. For long periods during the early and late stages of the glacial epoch, valley glaciers were undoubtedly active in deepening these three valleys as their separate ice streams flowed into the main trunk valley. While Lake Melville valley was completely ice filled, differential deepening of these individual valleys probably ceased and differential deepening probably then occurred chiefly at certain points in the main valley.
The valley occupied by Grand lake and the lower part of Naskaupi river is, after that of Hamilton river, the largest valley in the region, and trends nearly at right angles to Hamilton River and Lake Melville valley. Its direction corresponds in a general way with the strike of the gneissic rocks which the valley traverses. The northwesterly strike and south-westerly dip of the rocks appear very clearly to have controlled the trend of Grand Lake. All the promontories on the west side of the lake present distinctly steeper profiles than the slopes of those on the opposite side, as would be expected in such a strike valley.
The major features of the drainage system of this region, which were developed in Preglacial time as outlined above, were modified in many details by the covering of the Labrador ice-sheet. During the period when the region was covered by an ice-sheet and in the intervals between possible withdrawals and re-advances of the great ice-sheet of eastern North America, many modifications and minor changes occurred in that valley. These changes in the old Tertiary drainage system included the local deepening of valleys by glacial scour and the partial filling of valleys with glacial debris elsewhere. This cut-and-fill process, which the great valley glaciers continued for long periods both before and after maximum glaciation, transformed, in the interior, the normal rivers of Tertiary time into streams with numerous lake-like expansions. Other profound modifications of the valleys were produced during Pleistocene time when the whole region was depressed about 300 feet. It was at this time that the great system of sand-terraces 40 and marine and freshwater clays was added to the valleys.
In spite of the extensive character of the changes locally developed in the drainage system which Tertiary and earlier erosion has impressed on the region, the wide, mature valleys of preglacial origin are easily distinguished as to age from the narrow V-shaped gorge of Kenamu river, which has been developed in Quarternary time. There can be no doubt that