To state the matter briefly, one may say that almost everywhere in Ontario are deposits of glacial drift of Wisconsin age. In a few localities have been discovered beds which belong to earlier glacial and interglacial epochs. On the other hand, around Hudson Bay, around the Gulf of St. Lawrence, along St. Lawrence and Ottawa Rivers, and the Bay of Fundy are marine deposits, laid down after the Wisconsin ice had retired from those localities and while the region which had been occupied by this ice-sheet was depressed so much that the sea could enter the basins named.
The most interesting locality in Canada for the student of vertebrate palæontology is doubtless Toronto, because of the presence there of Pleistocene deposits belonging to more than one stage, and because of the discovery of several species of extinct vertebrates and of many mollusks, insects, and plants. For an understanding of the geology of the region Coleman’s papers must be studied, as well as those of authors cited by him. On the interglacial deposits three of Coleman’s papers may be especially cited (Jour. Geol., vol. IX, 1901, pp. 285–310; 10th Internat. Cong. Geol., 1906, Mexico, pp. 1237–1258; Bull. Geol. Soc. Amer., vol. XXVI, 1915, pp. 243–254).
According to Coleman’s figure 1 of the first paper cited, the known interglacial deposits in that region extend from the mouth of Humber River eastward beyond the mouth of Rouge River, a distance of about 22 miles, and away from the lake a distance of about 8 miles. Deposits have been found even 14 miles north of Toronto (Coleman, 1915, p. 246). Coleman’s sketch map of the region, taken from his paper of 1901, is here reproduced (fig. 3).
According to Coleman (paper of 1915, p. 243) there are known at Toronto five well-defined sheets of boulder clay, with four sheets of interglacial sand and clay separating them. So far as the writer knows, only the lowest of these beds have been described with any particularity. These lowest beds constitute the Toronto formation, and it is these which have furnished nearly all the fossil animals and plants discovered in that region. This Toronto formation is divisible into two portions, and these have been designated as the Don beds and the Scarboro beds. They are regarded as having been deposited in the valley of an ancient river running from Georgian Bay to Scarboro. Of these the Don beds are the older. Sections of these are found in Toronto and outside, especially along Don River. They have been laid down usually on a boulder clay, 1 to 9 feet thick, which itself reposes on Hudson River shales. At one point along the Don an interglacial river had cut through both the boulder clay and the shale to a depth of 16 feet. The Don deposits consist of varying layers of sands, gravels, and clays. At one point the section obtained amounted to about 27 feet; but this, combined with another, made up about 44 feet. At one place trunks, 12 or 15 feet long, of trees have been found, which were flattened into the surface of the boulder till; also shells of unios, which are embedded in clay close to the boulder till.
Fig. 3.—Region about Toronto, Ontario, showing location of Toronto and Scarboro Heights Pleistocene beds. From Coleman.
In 1913 (Ontario Bur. Mines. Guide Book No. 6, pp. 15–18), Professor Coleman presented a list of the species found in the Don beds. Of the plants 32 species of trees had been secured, among them the pawpaw, the red cedar, and the osage orange; 41 species of fresh-water mollusks were listed, of which 12 were Unionidæ.
As bearing on the climate, it may be said that there are 12 species of the genus Unio listed, of which 4 species are now known only from localities south of the St. Lawrence drainage; while 3 other species live in Lake Erie, but not in Lake Ontario. The plants are mostly trees; and several species, as the osage orange and the pawpaw, are now found only considerably farther south. One species of maple no longer exists. Penhallow gave it as his opinion that the flora points conclusively to the existence of climatic conditions of a character more nearly like that of the middle United States to-day. The unios now missing from that region give evidence to the same fact. For these reasons the Don deposits are spoken of as the warm-climate beds.
The Scarboro beds are finely displayed at Scarboro heights, a few miles east of Toronto. The thickness of the clay here amounts to about 94 feet. In these deposits have been found possibly mammoth or mastodon and caribou, but there is some uncertainty about these. Only 14 species of plants have been secured and these are trees; but apparently no mollusks have been reported. As an offset there are great numbers of beetles. Of these there have been described 72 species, and all are extinct except 2.
The trees, according to Penhallow, indicate a climate somewhat cooler than that now prevailing in that region. The same conclusion was reached by Scudder from his study of the insects. In his paper of 1901, Coleman took the view that the Toronto formation had been laid down in the interval between the Iowan and the Wisconsin glacial stages, that is, during what is now known as the Peorian. In the address of 1906, page 44, he appears to have been inclined to accept Leverett’s view that at least the Don beds belonged to the Sangamon stage. By 1915 (paper cited, p. 252) he had about concluded that the Toronto beds were as old as the Aftonian stage.