Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/920

 Lachine rapids at the Victoria tubular railway bridge two or three seasons back. And again a similar flood occurred in the winter of 1869.

But the most striking example of the action of anchor-ice that has come to my knowledge is that of Crab Island, situated in the midst of the River St. Lawrence, about 3 miles above the town of Cornwall. This island was situated between Barnhast' s Island and Cornwall Island. Mr. George Barnhast, a man far advanced in years, being over eighty years of age, well remembers this island. When he first knew it, its extent was about an acre and a half ; but he could plainly see, from the shoal-ground, that it must formerly have consisted of at least five or six acres. He had gathered wild grapes (Vitis vulpina) upon the island when a boy; and there were many bushes and small trees upon it at that time. Another old resident also tells me that he remembers its being about an acre in extent. Row Crab Island has entirely disappeared, though a strong ripple still indicates where its foundation or basis remains, though year by year the water is becoming deeper. The Rector of Cornwall, Archdeacon Patten, who kindly drew my attention to this fact, and furnished me with its early history, says, " Within my recollection, the water was shallower over it ; and when I first came to Cornwall (now 24 years ago), rafts of timber coming down the St. Lawrence were continually grounded upon it, whereas now it is a very unusual occurrence for one to be grounded there."

Mr. G. Barnhast says the ice is the chief cause of the island's removal. The anchor-ice accumulates in great quantities at the foot of the Long Sault rapids at St. Regis Island, at the western entrance of Lake St. Francis, in the smooth water, until at length it forms a dam across the whole river, which in consequence sets back until the rapids above become smooth water. The river then rises until it at times reaches 20 or 25 feet, inundating the adjoining elevated Long Sault or Cornwall Canal, until immature icebergs are formed of floes ; then the dam gives way, and the water suddenly subsides. These ice-accumulations often topple over, carrying with them masses of earth and boulders imbedded in them. By such masses Crab Island was gradually carried away piecemeal. And Mr. Barnhast states that he remembers one large rock above water that was at length tumbled into the deep water below. In like manner, from the rapids above his house on Barnhast's Island, the ice has brought down boulders and deposited them on the level space before his house, where several still remain.

The upper surface of the islands in this portion of the St. Lawrence is Postpliocene and Boulder-drift, lying over chalky sandstone strata of the Lower Silurian (Trenton) series. Within the precincts of the town of Cornwall, there is a large and dense accumulation of marine shells, chiefly Saxicava vagosa, Leda portlandica, Mya arenaria, &c, which still exist in the Gulf of St. Lawence. But this deposit, chiefly in sand, is at least 700 feet above the level of the sea. And the burial-ground of the parish church, with the structure (the Bishop Strachan memorial church), is situate in