414 PLEISTOCENE OF INDIANA AND MICHIGAN. 



Algonquin throughout all the region south of the isobase of Kirkfield was made during this 



three-outlet phase, the northern part while the Kirkfield outlet still carried more than hah the 



overflow and the southern part while the southern outlets carried more than half. The strong 



development of this beach indicates either pause or very slow uplift, although the fact that 



the lake was slowly rising upon the land also tended to give the waves maximum power and to 



make the beach strong. But although the upper beach belongs to the three-outlet phase, 



all the other Algonquin beaches belong to the Port Huron-Chicago stage. 



The magnitude of the uplift that affected Lake Algonquin in the north is shown by the 



o-reat increase of the vertical interval between the Nipissing beach, which is everywhere easily 



recognizable, and the highest beach of Lake Algonquin. Although this interval is only 10 feet 



in the area of horizontal ity, it widens to more than 175 feet at Mackinac Island and to nearly 



365 feet at Sault Ste. Marie. 



OUTLETS. 



The outlets of the third stage of Lake Algonquin were at Port Huron southward to the Lake 

 Erie basin (see p. 410), and at Chicago through Desplaines, Illinois, and Mississippi rivers 

 to the Gulf of Mexico. The Chicago outlet has been fully described by Mr. Leverett 1 and by 

 W. C. Alden. 2 



BEACHES OF THE PORT HURON-CHICAGO STAGE. 

 EARLY INVESTIGATIONS. 



The stronger of the beaches of Lake Algonquin, especially the very strong highest strand 

 and the associated heavy ridges of the upper group, were recognized as ancient shore lines and 

 referred either to the lakes or to the sea by many of the early explorers and settlers. Bayfield, 

 Houghton, Desor, Whittlesey, and others recognized these beaches in the Georgian Bay, northern 

 Huron, and Lake Superior basins. Later they were studied on the shores of Lake Michigan 

 near Chicago by Bannister 3 and by Andrews,* and in Wisconsin by Chamberlin. 5 But the first 

 tracing of the upper Algonquin beach and the first accurate measurements of its altitude in the 

 region of strong deformation were made by Spencer through independent work in Ontario, 

 and his results brought out the first clear conception of the northward differential uplift cr 

 warping of the land and of the direction and rate of the rise. 6 



In his work Spencer used a spirit level, and the accuracy of many of his determinations has 

 been verified by subsequent measurements made in the same way. Spencer did not trace the 

 beach continuously across the country nor map it in detail, but identified it from place to place 

 by certain quahties of strength and character. Nearly all his inferences as to its continuity 

 between points of observation appear to have been correct, but one important inferred exten- 

 sion of the beach beyond observation was erroneous. From its high level around Lake Simeoe 

 and Georgian Bay, Spencer showed how the beach descends rapidly, but at a decreasing rate, 

 along the east side of Lake Huron to Grand Bend. Beyond this he inferred its extension south- 

 westward in a gently declining plane so as to pass about 20 feet below present lake level at 

 Port Huron. Instead of this, as the writer found a few years later, the beach becomes horizontal 

 about at Grand Bend and passes thence into Sarnia at a uniform level of about 25 feet above 

 the lake. 



Spencer often noted the group of strong ridges close below the highest beach and occa- 

 sionally made brief mention of other shore lines at lower altitudes but appears not to have 

 undertaken to identify them from place to place or to have made many measurements of their 

 altitude. 



From 1890 to 1900 the writer carried on independent studies on the ancient shore lines of 

 the Great Lakes region. 7 The work extended over most of the lake region and in the northern 



i The Pleistocene features and deposits of the Chicago area: Bull. Chicago Acad. Nat. Sci. No. 11, 1897, pp. 55-64. 



2 Chicago folio (No. 81), Geol. Atlas U. S., U. S. Geol. Survey, 1902, p. 7. 



3 Bannister, H. M., Report on Cook County, HI.: Geology of Illinois, vol. 3, 1S68, pp. 240-244. 



1 Andrews, Edmund, The North American lakes considered as chronometers of postglacial time: Trans. Chicago Acad. Sci., vol. 2, 1870, pp. 1-24. 



s Chamberlin, T. C, Geology of Wisconsin: Wisconsin Geol. Survey, vol. 2, 1877, pp. 219-229. 



6 Spencer, J. W. , Deformation of Algonquin beach and birth of Lake Huron : Am. Jour. Sci., 3d ser., vol. 41, 1891, pp. 11-21. 



' See Bibliography, pp. 48-50; papers by F. B. Taylor bearing date earlier than 1900. 



