III. PROTOZOA AND ECHINODERM. (Post-pliocene-Canada.)

Fig. 1.

Fig. 2.

Tethea Logani, Montreal, (a) Mass of Spicules in clay; (b c d) Spicules, (natural size and magnified.)

Group of Common Foraminifera from Montreal. (magnified.) Polystomella crispa; Quinqueloculina seminulum; Polymorphina lactea, two varieties; Entosolenia globosa and E. costata.

Truncatulina lobulata. (magnified.)

Nonionina scapha.-Var. Labradorica. (magnified.) Fig. 5. Ophioglypha Sarsii, Duck Cove, St. John, N. B.

THE

CANADIAN NATURALIST

AND

Quarterly Journal of Science.

THE POST-PLIOCENE GEOLOGY OF CANADA.
By J. W. DAWSON, LL.D., F.R.S., F.G.S.

PART II.

-LOCAL DETAILS.-(Continued.)

5. Lower St. Lawrence-South Side.

The Report of the Geological Survey of Canada (1863), includes all that is yet known of the Post-pliocene formations at Gaspé, and thence upward to Trois Pistoles. According to this Report, the Boulder-clay and overlying sands and gravels are extensively spread over the Peninsula of Gaspé. On the Magdalen River they have been traced up to a height of 1600 feet above the sea, though marine shells are not recorded at this great height. Terraces occur at various elevations, and in one of the lower at Port Daniel, only fifteen feet above the sea, marine shells occur. On the coast westward of Cape Rosier, terraces occur at many places, and of different heights, and marine shells have been found ninety feet above the sea. I have not had opportunities to examine these deposits to the eastward of the place next

to be mentioned.

Trois Pistoles. At this place one of the most complete and instructive sections of the Post-pliocene in Canada, has been exposed by the deep ravine of the river, and by the cuttings for the Intercolonial Railway. The most important terrace at the

VOL. VI.

H

No. 3.

mouth of the Trois Pistoles River, that in which the railway cutting has been made, is about one hundred and fifty feet above the level of the sea, and is composed of clay capped with sand and gravel. At no great distance inland, there rises a second terrace one hundred and sixty feet higher than the first, or about three hundred and ten feet above the sea. front of this terrace is cut into two or more.

In some places the
It consists of clay

capped with sand and gravel, with some large stones and Laurentian boulders. Still farther inland is a third terrace, the height of which was estimated at four hundred to four hundred and fifty feet.

In the first mentioned of the above terraces, a very deep railway cutting has been made, exposing a thick bed of homogeneous. clay of a purplish gray colour and extremely tenacious. It contains few fossils; and these, as far as I could ascertain, exclusively Leda truncata. It is, in short, a typical Leda clay, and its thickness in this lower terrace can scarcely be less than one hundred and twenty feet. As the inland terraces are probably also cut out of it, this may be less than half of its maximum depth. Under the Leda clay a typical Boulder-clay had been exposed at one place in digging a mill sluice. It seemed to be about twenty feet thick, and rests on the smoothed edges of the shales of the Quebec group.

Though the Leda clay at the Trois Pistoles seems perfectly homogeneous, it shows indications of stratification, and holds a few large Laurentian boulders, which become more numerous in tracing it to the westward. A short distance westward of Trois Pistoles, it is seen to be overlaid by a boulder deposit, in some places consisting of large loose boulders, in others approaching to the character of a true Boulder-clay or associated with stratified sand and gravel. We thus have Boulder-clay below, next Leda clay, and above this a second Boulder drift associated with the Saxicava sand, and apparently resting on the terraces cut out of the older clays. This is the arrangement which prevails throughout this part of Canada. It is modified by the greater or less relative thickness of the Boulder-clay and Leda clay, by the irregular distribution of the overlying sands, and by the projec tion through it of ridges of the underlying rocks.

The section at Trois Pistoles may be represented as follows in descending order:

1. Sand and Gravel, capping the terraces cut in the previous

deposits, and forming slight ridges or eskers in some of the lower levels. It contains on the lower terraces a few shells of Leda and Tellina. At the bottom of this deposit there are seen in places many large boulders of Laurentian and Lower Silurian rocks, resting on the Leda clay below.

2. Leda Clay, exposed in the railway cutting and seen also in

the edge of the second terrace. Thickness one hundred and twenty feet or more. It holds a few large boulders and shells of Leda truncata-the latter uninjured and with the valves united.

3. Boulder clay, or hard gray till, with boulders and stones. Seen in a mill-sluice near the bridge, and estimated at twenty feet in thickness, at this place; though apparently increasing in thickness farther to the westward.

4. Shales of Lower Silurian age, seen in the bottom of the River near the bridge. They are smoothed over, but show no striæ, though they have numerous structure lines which might readily be mistaken for ice-striæ.

This

To the eastward of the mouth of Trois Pistoles River, the first terrace above-mentioned is brought out to the shore by a projecting point of rock. In proceeding westward toward Isle Verte, it recedes from the coast, leaving a flat of considerable breadth, which represents the lowest terrace seen on this part of the St. Lawrence, and is elevated only a few feet above the sea. flat is in many places thickly strewn with large boulders, probably left when it was excavated out of the clay. In proceeding westward the first or railway terrace of Trois Pistoles, inland of the flat above mentioned, is seen to consist of Boulder-clay, either in consequence of this part of the deposit thickening in this direction, or of the Leda clay passing into Boulder-clay. It still, however, at Isle Verte, contains a few shells of Leda truncata in tough reddish clay holding boulders.

Rivière-du-Loup and Cacouna.-The country around Cacouna and Rivière-du-Loup rests on the shales, sandstones, and conglomerates of the Quebec and Potsdam groups of Sir W. E. Logan. As these rocks vary much in hardness, and are also highly inclined and much disturbed, the denudation to which they have been subjected has caused them to present a somewhat

uneven surface. They form long ridges running nearly parallel to the coast, or north-east and south-west, with intervening longitudinal valleys excavated in the softer beds. One of these ridges forms the long reef off Cacouna, which is bare only at low tide; another, running close to the shore, supports the village of Cacouna; another forms the point which is terminated by the pier; a fourth rises into Mount Pilote; and a fifth stretches behind the town of Rivière-du-Loup.

The depressions between these ridges are occupied with Postpliocene deposits, not so regular and uniform in their arrangement as the corresponding beds in the great plains higher up the St. Lawrence, but still presenting a more or less definite order of succession. The oldest member of the deposit is a tough Boulderclay, its cement formed of gray or reddish mud derived from the waste of the shales of the Quebec group, and the stones and boulders with which it is filled partly derived from the harder members of that group, and partly from the Laurentian hills on the opposite or northern side of the river, here more than twenty miles distant. The thickness of this Boulder-clay is, no doubt, very variable, but does not appear to be so great as farther to the eastward.

Above the Boulder-clay is a tough clay with fewer stones, and above this a more sandy Boulder-clay, containing numerous boulders, overlaid by several feet of stratified sandy clay without boulders; while on the sides of the ridges, and at some places near the present shore, there are beds and terraces of sand and gravel, constituting old shingle beaches apparently much more recent than the other deposits.

All these deposits are more or less fossiliferous. The lower Boulder clay contains large and fine specimens of Leda truncata and other deep-water and mud-dwelling shells, with the valves attached. The upper Boulder-clay is remarkably rich in shells of numerous species; and its stones are covered with Polyzoa and great Acorn-shells (Balanus Hameri), sometimes two inches in diameter and three inches high. The stratified gravel holds a few littoral and sub-littoral shells, which also occur in some places in the more recent gravel. On the surface of some of the terraces are considerable deposits of large shells of Mya truncata, but these are modern, and are the kitchen-middens' of the Indians, who in former times encamped here.

Numbers of Post-pliocene shells may be picked up along the