The entire area of the great lakes is about 91,000 square miles. They are remarkable for the purity of their waters, which do not contain more than eight grains of solid matter to the gallon of 70,000 grains. The variations to which their level is subjected are common to all, and may be generally stated to be as follows:

1. The mean minimum level is attained in January or February.

2. The mean maximum level is in June.

3. The mean annual variation is twenty-eight inches. 4. The maximum variation in twelve years has been four feet and six inches.

5. There is no periodicity observable in the variations of their levels, and there is no flux and reflux dependent upon lunar influence.

The St. Lawrence carries past the city of Montreal 50,000,000 cubic feet of water in a minute, and in the course

of one year bears 143,000,000 tons of solid materials held in solution, to the sea. All the phenomena of a mighty river may here be witnessed on a stupendous scale, its irresistible ice masses, crushing and grinding one another in the depth of winter, its wide-spreading and devastating floods in spring, its swelling volume stealing on with irresistible power in summer, broken here and there by tumultuous and surging rapids or by swift and treacherous currents, or by vast and inexhaustible lakes. As it approaches the ocean it rolls on between iron-bound coasts, bearing the tributary waters of a region equal to half Europe in area, and subject to a climate which vainly endeavors to hold it frost-bound for fully one-third of the year. The whole valley of the St. Lawrence is a magnificent example of the power of water in motion, and the great lakes themselves are splendid illustrations of the "dependence of the geographical features of a country upon its geological structure."

The following table shows the relative magnitude of the great lakes of the St. Lawrence valley:

The greatest known depth of Lake Ontario is 780 feet; in Lake Superior, however, a line 1,200 feet long has, in some parts, failed in reaching the bottom.

GEOGRAPHICAL SURFACE OF CANADA.

The western peninsula, comprehending the rich tract of country west of an undulating escarpment or ancient sea

margin, reaching from Queenstown on the Niagara, round the head of Lake Ontario, and thence north to Georgian Bay, Lake Huron, is a gently sloping plain, deeply covered with drift clays; the highest part of this plain is at the Blue Mountains, abutting on Georgian Bay, where their northwestern escarpment is about 1,000 feet above Lake Huron. From the central townships of Proton and Luther, a low axis or water parting causes the rivers to discharge west into Lake Huron and east into Lake Erie, as far south as the head-waters of the Thames, which flows in a southwesterly direction to Lake St. Clair. Joining the ancient sea margin about half way between Lake Ontario and Nottawasaga Bay, Lake Huron, a ridge of drift, about 700 feet above where the Northern Railway crosses it, pursues a course roughly parallel to Lake Ontario, but with gradually diminishing altitude, and terminates near the Bay of Quinté. This ridge of drift blocks up a communication which once existed between Georgian Bay and Lake Ontario. There is strong evidence to prove that another. 'Niagara' formerly existed somewhere between Lake Huron and Ontario, probably in the neighborhood of the line of the Northern Railway. A direct artificial water communication between these lakes is now advocated. In the rear of these subordinate elevations, which only slightly diversify the great plain of western Canada, the Laurentide mountains, stretching from Lake Superior to Labrador, separate the valley of the St. Lawrence from the region tributary to Hudson's Bay. The Laurentides approach or form the north shores of the Gulf and River St. Lawrence from Labrador to near Quebec; they then retire from the river by degrees, and at Montreal are thirty miles from the St. Lawrence. They cross the Ottawa one hundred and fifty miles from Montreal, and, bending round, approach the St. Lawrence again in the direction of Kingston. From this point they run in a north-westerly direction, and form