Fig. 118.
- K. Mr. Ryland's house.
- h. Clay and sand of higher grounds, with Saxicava, &c.
- g. Gravel with boulders.
- f. Mass of Saxicava rugosa, 12 feet thick.
- e. Sand and loam with Mya truncata, Scalaria Grœnlandica, &c.
- d. Drift, with boulders of syenite, &c.
- c. Yellow sand.
- b. Laminated clay, 25 feet thick.
- A. Horizontal lower Silurian strata.
- B. Valley re-excavated.
I described in 1839 the fossil shells collected by Captain Bayfield from strata of drift at Beauport near Quebec, in lat. 47°, and drew from them the inference that they indicated a more northern climate, the shells agreeing in great part with those of Uddevalla in Sweden.[134-A] The shelly beds attain at Beauport and the neighbourhood a height of 200, 300, and sometimes 400 feet above the sea, and dispersed through some of them are large boulders of granite, which could not have been propelled by a violent current, because the accompanying fragile shells are almost all entire. They seem, therefore, said Captain Bayfield, writing in 1838, to have been dropped down from melting ice, like similar stones which are now annually deposited in the St. Lawrence.[134-B] I visited this locality in 1842, and made the annexed section, [fig. 118.], which will give an idea of the general position of the drift in Canada and the United States. I imagine that the whole of the valley B was once filled up with the beds b, c, d, e, f, which were deposited during a period of subsidence, and that subsequently the higher country (h) was submerged and overspread with drift. The partial re-excavation of B took place when this region was again uplifted above the sea to its present height. Among the twenty-three species of fossil shells collected by me from these beds at Beauport, all were of recent northern species, except one, which is unknown as living, and may be extinct (see [fig. 119.]). I also examined the same formation farther up the valley of the St. Lawrence, in the suburbs of Montreal, where some of the beds of loam are filled with great numbers of the Mytilus edulis, or our common European mussel, retaining both its valves and purple colour. This shelly deposit, containing Saxicava rugosa and other characteristic marine shells, also occurs at an elevated point on the mountain of Montreal, 450 feet above the level of the sea.[135-A]
Fig. 119.
Astarte Laurentiana.
- a. Outside.
- b. Inside of right valve.
- c. Inside of left valve.
In my account of Canada and the United States, published in 1845, I announced the conclusion to which I had then arrived, that to explain the position of the erratics and the polished surfaces of rocks, and their striæ and flutings, we must assume first a gradual submergence of the land in North America, after it had acquired its present outline of hill and valley, cliff and ravine, and then its re-emergence from the ocean. When the land was slowly sinking, the sea which bordered it was covered with islands of floating ice coming from the north, which, as they grounded on the coast and on shoals, pushed along such loose materials of sand and pebbles as lay strewed over the bottom. By this force all angular and projecting points were broken off, and fragments of hard stone, frozen into the lower surface of the ice, had power to scoop out grooves in the subjacent solid rock. The sloping beach, as well as the floor of the ocean, might be polished and scored by this machinery; but no flood of water, however violent, or however great the quantity of detritus or size of the rocky fragments swept along by it, could produce such long, perfectly straight and parallel furrows, as are everywhere visible in the Niagara district, and generally in the region north of the 40th parallel of latitude.[135-B]