Supposed Correlations 45 



Blue Island Ridge 46 



Bowlder Train 46 



Lakeward Extension of East Ridge 47 



Associated Till Plains 47 



Altitude and Slopes 47 



Thickness of Drift 48 



Structure of Drift 48 



Striae 52 



Tlie Chicago Outlet and Beaches of Lake Chicago 55 



Previous Writers 55 



The Chicago Outlet 57 



The Glacial Lake Chicago 64 



Upper, or Glenwood Beach 66 



Interval of Emergence 71 



Second, or Calumet Beach 72 



Third, or Tolleston Beach 74 



The Present Beach of Lake Michigan 79 



Acknowledgements 85 



ILLUSTRATIONS. 



Page. 



PI. 1. Glacial Map of North America 12 



PI. 2. Glacial Map of Illinois , 15 



PI. 3, Glacial Map of Chicago and Vicinity 23 



PI. 4, Profile Sections Across the Chicago Area 24 



Pig. 1. Bowlder and Peat Bed near Willow Springs 48 



Fig. 2. Disturbed Stratification near Willow Springs. 50 



Fig. 3. Striae at Stony Island 52 



Fig. 4, Striae at Stony Island 54 



Fig. 5. Striae at Stony Island 56 



Fig. 6. Striae on Bed of Chicago Outlet near Willow Springs 58 



Fig. 7. Grooves in Bed of Chicago Outlet near Lemont 60 



Fig. 8, Cut Terrace of the Upper Beach near Galewood 67 



