a, Vegetable soil. b, Gravel and sand. c, Clays. d, Limestone rock, slightly inclined.
Fig. 2.—Section at Niagara Falls, showing the strata cut through by the action of the Fall. Thickness of beds about 250 feet.
| a, Boulder clay and gravel—Post-pliocene. | |
| b, Niagara limestone c, Niagara shale d, Clinton limestone e, Medina sandstone | ┐Upper Silurian, │ with marine shells │ and ┘ corals. |
In deep mines and borings still more profound sections may be laid open, as in [Fig. 3], which represents the sequence of beds ascertained by boring with the diamond drill in search of rock salt near Goderich in Canada. Here we have a succession of 1,500 feet of beds, some of which must have been formed under very peculiar and exceptional conditions. The beds of rock salt and gypsum must have been formed by the drying up of sea-water in limited basins. Those of Dolomite imply precipitation of carbonate of lime and magnesia in the sea-bottom. The marls must have been formed largely by the driftage of sand and clay, while some of the limestone was produced by accumulation of corals and shells. Such deposits must not only have been successive, but must have required a long time for their formation.
Fig. 3.—Section obtained by boring with the diamond drill, near Goderich, Ontario, Canada, in the Salina series of the Upper Silurian. From a memoir by Dr. Hunt in the Report of the Geological Survey of Canada for 1876-7.
No. 1, Clay, gravel, and boulders—Post-pliocene.
Nos. 2, 4, 7, 9, 13, Dolomite or magnesian limestone, with layers of marl, limestone, and gypsum.
No. 3, Limestone with corals—Favosites, etc.
Nos. 5, 11, 15, 17, Marls with layers of Dolomite and anhydrous gypsum.
Nos. 6, 8, 10, 12, 14, 16, Rock salt.