GEOLOGY OF THE TORONTO REGION
valley, which it entered near Toronto. Probably the Ontario basin did not then exist and the valley sloped eastwards toward the sea.
When the first record begins the surface possessed a higher relief than now, the escarpment rising as cliffs of 300 or 400 feet, and the old river valley at Toronto having a depth of at least 200 feet below the general level.
The greater part of the region is covered with glacial deposits, especially boulder clay, and moraines are frequent, sometimes rising as tumultuous hills as in the Oak Ridges north of Toronto, at others having low and inconspicuous forms. They have been worked out in much of the region by Mr. F. B. Taylor, but no general map of the glacial deposits has yet been published. With the moraines in various places there are kame deposits of coarse gravel and sand where sub-glacial rivers emptied, and in some cases narrow esker ridges of sand indicate the course of such rivers beneath the ice. The general surface of the boulder clay is apt to be gently rolling, as north of Toronto, but in some places there are drumlin hills of a more striking kind.
The boulder clay is charged with a great variety of stones, including Archaean rocks, such as granite, gneiss, diorite and crystalline limestone, and Palaeozoic rocks, such as limestones, shales and sandstones of the Ordovician. The matrix is commonly bluish