CONTENTS. 



Abstract of volume 18 



Chapter I. Introduction, by Frank Leverett » 23 



Outline of area and subjects of discussion 23 



Field work 23 



Glacial gathering grounds and ice lobes 24 



Glacial succession : 25 



Oldest recognized drift 25 



First or Aftonian interglacial stage 26 



Kansan drift 26 



Second or Yarmouth interglacial stage 26 



Soil and weathered zone 26 



Loess 26 



Illinoian and Iowan drifts 26 



Third or Sangamon interglacial stage 27 



Post-Sangamon or main loess (Iowan?) 27 



Peorian or postloessial soil and weathered zone 27 



Wisconsin drift 27 



Location of the border 27 



Earlier and later Wisconsin 28 



Retreats and readvances of the ice 30 



Grouping of the moraines 30 



Evidence of readvance of the ice 31 



Chronology of the Wisconsin ice sheet 31 



Stage and substage 31 



Calculation of time 32 



Retardation of movement in the Saginaw lobe 32 



Bibliography 33 



Chapter II. Physical features, by Frank Leverett 55 



Topography 55 



Altitude. 55 



Michigan 55 



Indiana 56 . 



Relief 56 



Indiana 56 



Michigan 57 



Drainage 58 



Lakes 58 



Indiana 58 



Michigan 58 



Streams 59 



Preglacial drainage 59 



Present-day drainage systems 60 



Development of present drainage ' 60 



Thickness of the drift : 61 



Chapter III. Pre-Wisconsin drift and associated deposits, by Frank Leverett 62 



Limit of glaciation 62 



Illinoian and pre-Illinoian (?) deposits 63 



Complexity of the boundary 63 



Buried soil 63 



Minerals in the drift 64 



Copper 64 



Gold : 64 



Diamonds 64 



