670 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [June 22, 
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. 
Now 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 recol- 
lection, 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, car- 
ryling 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. Law- 
rence is Postpliocene and Boulder-drift, lying over chalky sand- 
stone strata of the Lower Silurian (Trenton) series. Within the 
precincts of the town of Cornwall, there is a large and dense accu- 
mulation of marine shells, chiefly Saxicava vagosa, Leda portland ica, 
Mya arenaria, &c., which still exist in the Gulf of St. Lawe nce. 
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 
