ONTARIO, a province of Canada, having the province of Quebec to the east, the states of New York, Ohio, Michigan, Wis consin, and Minnesota to the south, Manitoba to the west, and part of Hudson Bay with James Bay to the north. In most cases the actual boundary consists of rivers or lakes, the Ottawa to the north-east, the St. Lawrence and its chain of lakes and rivers to the south as far as Pigeon river, which separates Ontario from Minnesota. From this it follows small rivers and lakes to the Lake-of-the-Woods, which lies between Ontario, Minnesota and Manitoba. From Lake Temiscaming northwards the eastern boun dary is the meridian of 79° 3o'.
Physical Geography.—Ontario extends i,000 m. from east to west and 1,050 from north to south, between latitudes 57° and 42°, including the most southerly point in Canada. Its area is 407,262 sq.m. (41,382 water), and it is the most populous of the provinces, nine-tenths of its inhabitants living, however, in one tenth of its area, between the Great Lakes, the Ottawa and the St. Lawrence. This forms part of the plain of the St. Lawrence, under lain by Palaeozoic limestones and shales, forming a good soil.
The south-western part is naturally divided into two tracts by the Niagara escarpment, a line of cliffs capped by hard Silurian limestones, running from Queenston Heights near the falls of Niagara west to the head of Lake Ontario near Hamilton, and then north-west to the Bruce Peninsula on Georgian Bay. The tract north-east of the escarpment has an area of 9,00o sq.m. and an alti tude of 25o to i,000 ft., and the south-western tract includes 15,000 sq.m. with an elevation of 600 to 1,700 feet. In the last petroleum, natural gas, salt and gypsum are obtained, but else where in southern Ontario there are no economic minerals except building materials. Covering the higher parts there are rolling hills of boulder clay or moraines ; while the lower levels are plains gently sloping toward the nearest of the Great Lakes and sheeted with silt deposited in more ancient lakes when the St. Lawrence
outlet was blocked with ice at the end of the glacial period. The old shore cliffs and gravel bars of these glacial lakes are still well marked topographical features, and provide favourite sites for roads, towns and cities. St. Catharines, Hamilton and Toronto are on the old shore of Lake Iroquois, the lowest. The Niagara escarpment mentioned above is the cause of waterfalls on all the rivers which plunge over it, Niagara Falls being, of course, the most important. Between the Palaeozoic area near Ottawa, and Georgian Bay to the north of the region just referred to, there is a south ward projection of the Archaean protaxis consisting of granite and gneiss of the Laurentian, enclosing bands of crystalline lime stone and schists, which are of interest as furnishing the only mines of "Old Ontario." From these rocks in the Ottawa valley are quarried or mined granite, marble, felspar, talc, mica and graphite.
While all the larger cities and most of the manufacturing and farming districts of the province belong to southern Ontario, there is in process of development a "New Ontario," stretching for hundreds of miles to the north and north-west of the region just described and covering a far larger area, chiefly made up of an cient rocks forming the Archaean protaxis. The rocky hills of the tableland to the north long repelled settlement, the region being looked on as a wilderness useless except for its forests and its furs, but the finding of great ore deposits, the opening up of farming areas and the development of the wood pulp industry are constantly extending settlement toward the north. The build ing of the Canadian Pacific Railway led to the discovery of the Sudbury nickel region, where segregations of nickel-copper ores which occur round the edge of a sheet of norite supply 90 per cent. of the world's nickel, large amounts of copper and thousands of ounces of gold, silver, platinum and palladium. The Frood mine is known to contain 200,000,000 tons of ore.