INTRODUCTION. 31 



Huron and Erie basins back to the Port Huron morainic system. The moraines of this group 

 are relatively weak except in the vicinity of the junction of the Saginaw and Lake Michigan 

 lobes and between the Saginaw and Huron-Erie lobes. 



The fifth group embraces a series of moraines which is clearly separable from earlier moraines 

 on the western side of the Lake Michigan basin and in part of its course on the eastern side, 

 and which appears to be correlated with the Port Huron system of moraines in the Huron 

 basin. In Wisconsin it includes the series of red-clay moraines which are found from Milwaukee 

 northward. On the Michigan side its correlatives embrace the Whitehall moraine, which is 

 traceable northward from the vicinity of Muskegon, and some later moraines which appear 

 on the borders of Lake Michigan farther north. Of these last, two ridges that lead north from 

 near Manistee, Mich., seem to correlate with ridges on the Wisconsin side near Two Rivers; 

 they were formed subsequent to the development of the Glenwood and Calumet beaches of 

 Lake Chicago and the series of Arkona beaches in the Huron-Erie basin, for they override 

 the northern ends of these beaches and thus show a readvance of the ice. On retreating from 

 this morainic system the ice melted away from the Lake Michigan and Huron basins. 



Later groups exist in the region south of Lake Superior and probably still others north of 

 the lake in Canada, but these lie outside the region embraced in the present discussion and they 

 have as yet been but partly worked out. 



EVIDENCE OF READVANCE OF THE ICE. 



Readvance of the ice along at least a portion of the length of these bulky morainic systems 

 is more or less evident. At its western end, from Peoria, 111., northward, the Bloomington 

 system overrides not only the weak moraines of the Champaign system but even extends into 

 the ground occupied by the Shelbyville system and makes it impossible to differentiate the 

 two. The readvance in eastern Illinois and farther east appears to have been less pronounced, 

 the Kalamazoo and Valparaiso systems being separated from the Bloomington by fewer moraines 

 in Illinois than in northwestern Indiana. In the Port Huron morainic system the evidence of 

 readvance is very clear, especially on the peninsula or "thumb" of Michigan, between the 

 southern part of Lake Huron and Saginaw Bay, where, as shown by Mr. Taylor (p. 362), 

 the readvance caused a rise of the waters of a glacial lake outside the ice. 



The supposed correlatives of the Port Huron morainic system in the Lake Michigan basin 

 are more widely spaced than in the Huron basin; an outer member on the Wisconsin side con- 

 tains a red drift carried over a drift of lighter color, as noted by Chamberlin and Alden, and 

 later members on each side of the lake override the two higher beaches of the glacial lake Chicago, 

 which occupied the south part of the Lake Michigan basin. 



CHRONOLOGY OF THE WISCONSIN ICE SHEET. 



STAGE AND SUBSTAGE. 



The great morainic systems noted can scarcely be classed as recessional moraines. Instead 

 they appear to have been formed at the culmination of a readvance of more or less consequence. 

 These readvances are of a rank subordinate to that of glacial stages such as the Wisconsin, the 

 Illinoian, and the Kansan and seem to require a distinct designation. They appear to be of 

 similar rank to the readvances in the Alps that produced the Buhl, the Gschnitz, and the Daum 

 moraines and to represent perhaps similar divisions of the glacial stage. The term "stadium," 

 which is used in the Alps region for the part of the glacial stage falling between two marked 

 readvances of the ice, marks an areal oscillation rather than a time interval. It seems preferable 

 therefore to use the term "substage." Thus the Bloomington substage covers the time of depo- 

 sition of the Bloommgton morainic system and of all the later moraines back to the Kalamazoo- 

 Mississinawa morainic system, mcluding any that have been overridden by the latter system. 

 The Kalamazoo or Mississinawa substage covers the time of deposition of the moraines of the 

 contemporaneous Kalamazoo and Mississinawa systems and of all moraines back to or over- 

 ridden by the Port Huron morainic system. 



