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STAGES OF RECESSION OF THE NORTH AMERICAN ICE-SHEET. THE

AMERICAN JOURNAL OF SCIENCE

[THIRD SERIES.]

ART. I.-Late Glacial or Champlain Subsidence and Reëleva

tion of the St. Lawrence river basin; by WARREN UPHAM. (With Plate I.)

The accompanying map (Plate I) shows the maximum area covered by the ice-sheet in the St. Lawrence basin and adjoining portions of the United States and southern Canada, with approximate outlines of the glacial boundary at successive stages of its retreat. The Champlain epoch or part of the Pleistocene period including these stages of glacial recession was begun and ended, respectively, by downward and upward epeirogenic movements. Ît comprised the time of departure of the ice-sheet, with many small and large glacial lakes temporarily formed by its receding barrier, and with marine submergence to hundreds of feet above the present shore lines. The Late Glacial subsidence appears to have been principally completed before the retreat of the ice and deposition of the Champlain lacustrine and marine beds; but the following uplift was in progress, advancing as fast as the ice receded, from the beginning to the end of Champlain time.* Indeed, considerable parts of the glaciated areas of North America and Scandinavia are still undergoing small and slow oscillatory movements, not having yet, during the short Postglacial period, fully reached isostatic repose.

* For a discussion of the part of this movement reëlevating the upper Mississippi region, the area of the glacial Lake Agassiz in the basin of the Red river of the North and Lake Winnipeg, and the country surrounding Hudson Bay, see the Journal of Geology, vol. i1, pp. 383–395, May-June, 1894. The dynamic causes of epeirogenic movements, and their relations to the Glacial period as the probable causes of both its beginning and end, are partly considered in that paper, but more fully in an appendix of Wright's Ice Age in North America, 1889, pp. 573-595, this Journal, III, vol. xlvi, pp. 114-121, Aug., 1893, and the Geol. Magazine, IV, vol. I, pp. 340–349, Aug., 1894.

Au. JOUR. Sci.—THIRD SERIES, Vol. XLIX, No. 289.—Jan., 1895.

!

Evidence from the Beaches of the Glacial Lakes in the St.

Lawrence basin. Well marked old channels of outflow are found extending southward, at the levels of the deserted beaches, from Lake Agassiz and from the glacial lakes which are now represented by the diminished, but still large, modern lakes Superior, Michigan, Huron, Erie, Ontario, and Champlain. The ontlets prove that the great Pleistocene water bodies which occupied these basins were lakes, not gulfs or arms of the sea ; and the differential uplifts of the basins, increasing toward the central part of the area of the continental ice-sheet, show that no land barriers, but the ice itself in its retreat, held in these lakes on their northward sides.

The basin of the St. Lawrence during the glacial recession held successively, and in part contemporaneously, no less than eight important glacial lakes, distinguished by their different areas, heights, and places of outlet. They are named the Western Superior and Western Erie glacial lakes; Lake Warren, the most extensive, into which the two foregoing were merged; Lake Algonquin, the successor of Lake Warren in the basins of Lakes Huron, Michigan, and Superior ; Lake Lundy, the glacial representative of Lake Erie ; Lake Iroquois, in the basin of Lake Ontario; Lake Hudson-Champlain ; and Lake St. Lawrence, into which the two last named became merged. The glacial Lake St. Lawrence, which is the only one of the series hitherto unnamed, extended over the Ottawa, Champlain, and St. Lawrence valleys previous to the melting away of the ice barrier, remaining latest in the vicinity of Quebec, by which event the sea, at a lower level than the former lake, was admitted to these valleys.

The Western Superior glacial lake.* - In the west part of the basin of Lake Superior the receding ice-sheet held a lake which outflowed southward through northwestern Wisconsin, across the present watershed between the Bois Brulé and St. Croix rivers. The highest shore line of this lake at Duluth is 535 feet above Lake Superior (which has a mean level 602 feet above the sea); on Mt. Josephine, about 130 miles northeast from Duluth, its height, according to leveling by Dr. A. C. Lawson,t is 607 feet; and at L'Anse and Marquette, Mich., 175 and 225 miles east of Duluth, it is found by Mr. F. B. Taylorf about 590 feet above the lake. The northeastward

* Proc. A. A. A. S., vol. xxxii, for 1883, p. 230. Geol. and Nat. Hist. Survey of Minnesota, Final Report, vol. ii, 1888, p. 642; Twenty-second Ann. Rep. for 1893, pp. 54-66 (first use of this name). Bulletin Geol. Soc. Am., vol, ii, 1891, p. 258. Am. Geologist, vol. xi, p. 357, May, 1893; and vol. xiv, p. 63, July, 1894.

† Minnesota Geol. Survey, Twentieth Ann. Rep. for 1891, pp. 181-289, with map and profiles.

I am. Geologist, vol. xiii, pp. 316–327 and 365-383, with maps, May and June, 1894.

uplift averages seven inches per mile; and the eastward ascent is approximately three inches per mile. The latest and lowest of the Western Superior lake beaches observed at Duluth, occupied by the “boulevard” or pleasure driveway, 475 feet above the lake, on the bluffs back of the city, appears to have an ascent of only about 35 feet in the distance to Mt. Josephine, showing that the uplift of the land was quite rapidly in progress while the ice front still maintained the lake at the St. Croix outlet. Not long after the glacial retreat passed eastward beyond Mt. Josephine and Marquette, this lake was lowered and merged with Lake Warren across the lowlands of the northern peninsula of Michigan. The vertical interval between the final stage of the Western Superior Lake and the level of Lake Warren shown by its earliest beach at Duluth was about 60 feet. Thenceforward the outlet of Lake Warren past Chicago carried away the drainage from the glacial melting and rainfall of the Superior basin.

The Western Erie glacial lake.* -Outflowing from the southwestern end of the Lake Erie basin by a large abandoned watercourse, which reaches from Ft. Wayne, Ind., where the St. Joseph's and St. Mary's rivers unite to form the Maumee, across the present watershed to the Wabash river, this glacial lake formed two distinct beaches, named by N. II. Winchell the Van Wert and Leipsic ridges, separated by a vertical interval of 15 to 20 or 25 feet. The upper or Van Wert beach, with its crest varying in altitude from 200 to 220 feet above Lake Erie (whose mean height is 573 feet above the sea), extends about 75 miles east to Findlay, Ohio, and nearly an equal distance northeast past Bryan, Ohio, to the vicinity of Adrian, Mich., if not farther. At Findlay the lake while forming this beach, as Winchell and Leverett have shown, was bounded on the north by the ice-sheet then forming the Blanchard moraine. The second or Leipsic beach of the Western Erie Lake, ranging in height from 190 to 210 feet, runs from Ft. Wayne eastward 175 miles to its termination, as described by Leverett, at the line of a later moraine close south west of

*G. K. Gilbert, this Journal, III, vol. i, pp. 339–345, with map, May, 1871; Geology of Ohio, vol. i. 1873, pp. 540-556, with two maps. N. H. Winchell, Proc. A. A. A. S., vol. xxi, for 1872, pp. 171-179; Geology of Ohio, vol. ii, 1874, pp. 56, 431-433, etc. J. S. Newberry, Geology of Ohio, vol. ii pp. 46-65, with three maps and numerous sections. E. W. Claypole, “ The Lake Age in Ohio," Trans. Geol. Soc. Edinburgh, 1887, p. 42, with four maps. G. F. Wright, The Ice Age in North America, 1889, chapter XV (with reproduction of Prof. Claypole's maps, that of Lake Erie-Ontario being on p. 355). J. W. Spencer, this Journal, III, vol. xli, p. 208, with map, March, 1891; Bulletin, Geol. Soc. Am., vol. ii, 1891, pp. 465-476, with map. Frank Leverett, this Journal, III, vol. xliii, pp. 28!-297, with map, April, 1892. Warren Upham, Bulletin, Geol. Soc. Am., vol. ii, p. 259; Minnesota Geol. Survey, Twenty-second Ann. Rep. for 1893, p. 62 (first use of the name Western Erie Glacial Lake).

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