Page:The American journal of science, series 3, volume 49.djvu/25

Rh Beelevation of the St. Lawrence river basin. 7

miles onward, across Lake Superior to Kaministiquia, where the shore is 455 feet above that lake, the rate of northward ascent is reduced to only a half of a foot per mile.

Along a west to east course, the Nelson beach (named by Taylor in the vicinity of North Bay, Lake Ni pissing, probably not distinct from the Bel more beach in Ohio and northward to Mackinac island) is 385 feet above Lake Superior at Duluth ; 410 feet at Houghton, having an eastward ascent of 25 feet in 150 miles; 414 feet at the Sault Ste. Marie, running level for 200 miles east from Houghton ; and about 538 feet at the north side of Lake JSh'pissing, or 497 feet above that lake, and 1,140 feet above the sea. In the distance of 220 miles from Sault Ste. Marie to Lake Nipissing this beach now shows an ascent of 126 feet, or about seven inches per mile. These figures, with the preceding from Houghton to the north side of Lake Superior, justify to a remarkable degree Dr. Lawson's opinion that the ancient shore lines of Lake "Warren in the Superior basin remain parallel with* the water level of to-day. A.s compared with Chicago, the country enclosing Lake Su- perior has been uplifted 400 to 450 feet ; and the greater part of the differential elevation, expressed by tilting, took place upon the west to east belt of the northern peninsula of Mich- igan.

Three beaches of Lake Warren are mapped by Spencer and named the Ridge way, Arkona, and Forest beaches in Ohio, northwestern Michigan, and the province of Ontario north of Lake Erie. These probably represent the three noted at Chicago and about the south part of Lake Michigan. Farther north the number of distinct shore lines is much increased. In and near Duluth I find eight beaches referable to Lake Warren, the lowest being 50 feet above Lake Superior. On northern portions of the Lake Superior coast several of these seem, as shown by Lawson's observations with leveling, to be each represented by two or more shores, separated by vertical intervals of 10 feet or more. Most of the northern beaches, it should be remarked, are very feebly developed, even in the most favorable situations for their formation, and are not dis- cernible along the far greater part of the lake borders. Dur- ing all the time of differential uplifting of the Lake Warren basin and sinking of the water surface, whenever the dimin- ishing lacustrine area was nearly unchanged for a few years or longer, the erosion and deposition effected by the great waves of storms, and the tribute of streams forming deltas, recorded these shore lines. *

Lakes," Am. Geologist, vol. xiv, pp. 298. 301, Nov., 1894), supposes that an out- flow from Lakes Superior, Huron, Michigan, and PJrie, passed by the way of
 * Prof. Spencer, in his latest paper ("A Review of the History of the Great