By a Canadian Act of 1858, the harbour of Quebec, for the purposes of the Act, is defined as extending from the Cap Rouge river, about eight miles above Quebec, to the Montmorency, about the same distance below the city. At Quebec, and for many miles above, the St. Lawrence is a tidal river. Below Quebec the river flows due north-east, and is divided into two channels by the island of Orleans, which also lies due north-east and south-west, being twenty miles long with a maximum breadth of six miles. The inland--the south-western--end of the island points directly at the rock of Quebec, which runs out from the northern shore of the St. Lawrence, facing straight down the river, at four miles distance from the island. The two channels, looking up stream, unite at the end of the island, and form a semicircular basin just below Quebec, where the northern shore recedes. Immediately above this basin the rock of Quebec on the north of the river, and Point Levis on the southern mainland, jut out towards each other, narrowing the St. Lawrence to a breadth of considerably less than a mile. Above Quebec the upward course of the river is still south-west by west. The northern bank is continuously steep, and at five to six miles' distance from Quebec on this side is Sillery Cove. {298} Between two and three miles further on, nearly due west, is Cap Rouge. Over against Sillery the Chaudière river flows in from the south, forming in old days a possible route to the St. Lawrence for those who followed up the course of the Kennebec from the coast of Maine.[9] [Footnote 9: See above, p. 123.] Miles of river-side cliff culminate in the promontory on which Quebec stands, and the south-western end of which is known as Cape Diamond. From the river above the town, Quebec, if man combined with nature, was almost inaccessible. Below, the eastern side of the city is girt by the winding River St. Charles, beyond which are the meadows of Beauport, with shoals in front and high ground behind; and, past the little Beauport river, which is very roughly equidistant from the St. Charles and the Montmorency, the northern bank of the St. Lawrence is again more or less fringed with steep ground as far as, and beyond, the falls, over which the Montmorency takes its way into the great river. [Sidenote: _The strength of the French position._]