Reelevation of the St. Lawrence river basin. 11
Lake Lroquois* — This glacial lake, outflowing at Rome to the Mohawk and Hudson, occupied less area in the west part of the Lake Ontario basin during its earliest stage than during the later and probably longer enduring lake stage by which the high Iroquois beach in that region was formed. Previous to the date of the western development of the Iroquois beach, the early water level stood at one time only a little higher than the present Lake Ontario at Toronto and Scarboro Heights, 6 to 15 miles east of Toronto, as compared with the altitude, doubtless absolutely lower than now with regard to the sea, which the land then held in that part of the lake basin. This is shown by the occurrence of fossil fresh-water mollusks of lourteen species, and wood of ash, oak, and American yew, in beds at Toronto, described by Coleman, which now are 33 to 51 feet above Lake Ontario, or 280 to 298 feet above the sea. All the mollusk species are now living; but four are restricted, so far as known, to waters tributary to the Mississippi. A boulder-bearing surface deposit above these beds proves that the front of the ice-sheet was not far distant ; but the climatic conditions of that time, clearly indicated by the fauna and flora, were as mild as now. There next ensued, probably, a gradual rise of the lake, due to an uplifting of the country about its outlet at Rome, until it stood at the level of the well defined Iroquois beach, which has a height at Toronto of about 200 feet above Lake Ontario. Thick fossiliferous delta deposits had been, meanwhile, brought into the north edge of the lake at Toronto and several miles eastward along the lake- cliif section of Scarboro Heights, described by Hinde ; and re- peated re-advances of the ice-front, one during, and another after, the delta accumulation, formed, at the locality last noted, two deposits of till or boulder-clay.
In a limited sense the Toronto and Scarboro fossils may be called Interglacial, since they lie between deposits of glacial drift ; but they seem better referred to moderate oscillations of the ice boundary than to the distinct glacial epochs which Coleman and Hinde infer from them. Both these beds and
- J. W. Spencer, "The Deformation of the Iroquois Beach and Birth of Lake
Ontario," this Journal. Ill, vol. xl, pp. 443-451, with map, Dec, 1890 ; and papers previously cited. Thomas Roy (in paper by Sir Charles Lyell), Proceed- ings Geol. Soc, London, vol. ii. 1837, pp. 537, 538. Sir Charles Lyell, Travels in N. A., in 1841-42. vol. ii, chapter xx. E. J. Chapman, Canadian Journal, new series, vol. vi, 1861, pp. 221-22y, and 497, 498. Sand ford Fleming, Can. Jour., same vol. vi. pp. 247-253. GTeorge J. Hinde, Can. Jour., vol. xv, 1877. pp. 388- 413. A. P. Coleman, Am. Geologist, vol. xiii, pp. 85-95, Feb. 1894. Geol. Sur- vey of Canada, Report of Progress to 1863, pp. 912, 913. James Hall, Geology of New York. Partiv, 1843, pp. 348-351. Baron Gerard de Geer, "On Pleistocene Changes of Level in eastern North America." Proc. Boston Soc. Nat. Hist., vol. xxv, 1892, pp. 454-477, with map; also (excepting the map) in Am. Geologist, vol. xi, pp. 22-44, Jan., 1893. G. K. Gilbert, F. B. Taylor, B. W. Claypole, G. F. Wright, and Warren Upham, as cited for Lakes Warren and Algonquin.
