NATURAL HISTORY, TORONTO REGION
at Longford, south of Washago, near the northern branch of the Grand Trunk Railway on Lake Couchiching, and also at Kingston, at the east end of Lake Ontario.
The limestone may rest immediately on the steeply tilted gneiss, or there may be a thin sheet of coarse sandstone or conglomerate at the bottom. There is no doubt that the Black River beds once extended farther north and are now being stripped from the older crystalline rocks, exposing once more the Pre-Cambrian continental surface.
The Black River limestone is used for building stone and for lime-burning. It is not highly fossiliferous, the commonest fossils being Columnaria
halli, Calapoccia canadensis, Maclurea logani and Gonioceras anceps.
Immediately above the solid limestones mentioned above there is often a limestone formed in thinner sheets with partings of shale, the Trenton limestone. This occurs on the east side of Lake Simcoe, along Trent River, and at several points on the shore of Lake Ontario, such as Cobourg, Port Hope and Trenton. It is much thicker than the Black River and is richer in fossils. The beds are so gently tilted that they appear horizontal to the eye, but by comparing the same horizon at different points a dip toward the southwest of thirty or thirty-five feet to the mile has been found.
The following fossils are frequently found in the Trenton rocks: