Reelevation of the St. Lawrence river basin. 13
cally. From the lower and mam Lundy beach the water fell about 4S0 feet to the earliest stage of Lake Iroquois when the Toronto fossil shells lived in the edge of that lake, excepting that here again some undetermined amount must be subtracted to compensate the concurrent rise of the land. Adding these vertical intervals together, we have 635 feet, which probably may be reduced 100 feet, more or less, for the effects of the accompanying epeirogenic uplift. We have left some 500 or 550 feet, to be subtracted from the altitude of the old Chicago outlet of Lake Warren, believed to have been then approxi- mately as now, 590 feet above the sea, to give the earliest alti- tude of the Koine outlet. It thus appears, as I concluded from a similar computation four years ago, that the Rome outlet was at first only 50 or 100 feet above the sea level.* It was gradually uplifted, participating in the differential rise of the whole Ontario basin, to about 300 feet above the sea while the outflow continued here, and to probably 350 feet or more, lack- ing less than 100 feet of its present height, by the time when the much farther retreat of the ice permitted the extension of the sea to Ogdensburgh and Brockville, on the St. Lawrence river near the mouth of Lake Ontario. Intermediate between Lake Iroquois and the Cham plain incursion of the sea, the glacial Lake St. Lawrence, into which Lake Iroquois was merged by the retreat of the ice-sheet from the northern side of the Adirondacks, filled the Lake Ontario basin for a con- siderable time at levels below the Iroquois beaches.
As the area of Lake Warren was being differentially much elevated during the earlier existence of that lake, and as the area of Lake Algonquin was similarly uplifted in part or wholly contemporaneously with the Iroquois basin, so this region was being rapidly raised and tilted upward to the north and east while the lake level, held constantly without import- ant downward cutting at the Rome outlet, inscribed many shore lines on the slowly moving land. All the movement throughout the whole region probably was upward ; but the position of Rome, and its greater rise than western parts of the basin during the existence of Lake Iroquois, caused the old beaches westward to have now declining gradients.
Lake Hudson- Charwplain. — The absence of marine fossils
- Bulletin Geol. Soc. Am., vol, ii, pp. 260-r262.
f Warren T7pham. Bulletin Geol. Soc. Am., vol. i. p. 566; vol. ii, p. 265; vol. iii, pp. 484-487 (first using this name). C. H. Hitchcock, Geology of Vermont, 1861. vol. i, pp. 93-167, with map. J. S. Xewoerry, Pop. Sci. Monthly, vol. xiii, 1879, pp. 641-660. F. J. H. Merrill, this Journal. Ill, vol. xli, pp. 460-466, June, 1891. W. M. Davis. Proc. Boston Soc. Xat. Hist., vol. xxv, 1891, pp. 318-334. S. Prentiss Baldwin, " Pleistocene History of the Champlain Valley," Am. Geolo- gist, vol. xiii, pp. 170-184, with map, March, 1894. Baron de Geer, as cited for Lake Iroquois.
