VI CONTENTS. 



Page. 



Chapter VI. — The Sangamon soil and weathered /one 125 



Chapter VII. — The low an drift sheet and associated deposits 131 



The Iowan sheet of the Illinois lobe - 131 



Distribution or extent - 131 



Topographic expression 134 



Thickness of the drift 136 



Structure of the drift 137 



Strise 140 



Probable extent of Iowan drift sheet beneath the Wisconsin 141 



Probable extent of Iowa portion of Iowan drift 144 



Relation of the Illinois and Iowa ice lobes 151 



The Iowan loess 153 



Distribution - - 153 



Variations in thickness 155 



Structure -- : - 156 



Fossils - - l fi 5 



Mode of deposition 176 



Chapter VIII. — The Peorian soil and weathered zone (Toronto formation?) 185 



General statemeut 185 



Soil and peat between the Iowan and Wiscons : -i drift sheets 185 



Leached loess beneath the Wisconsin drift 187 



Iowan outline compared with succeeding and preceding glaciations J88 



Change in attitude of the land 188 



Length of the Peorian stage .- 188 



The Toronto formation 189 



Chapter IX.— The early Wisconsin drift sheets 191 



General statement 191. 



Section I. Shelby ville morainic system 192 



Extent of the Shelbyville sheet 192 



Shelby ville moraine - 192 



Distribution - . . . . 193 



Relief 194 



Range in altitude - 194 



Surface contours 195 



Structure and thickness of drift , 197 



Character of out wash 208 



Inner-border tract 213 



Topography - 213 



Thickness of drift 213 



Structure of drift -.- 213 



Cerro Gordo moraine - 218 



Distribution 218 



Topographic expression 218 



Structure of the drift 219 



Character of out wash 221 



Inner-border tract 222 



Section II. Champaign morainic system 223 



Distribution - 223 



Relief 225 



Range in altitude 226 



Surface contours 227 



Thickness and structure of drift 231 



Character of outwash 237 



Associated till plains 239 



Section III. Pdoomington morainic system 240 



Distribution 241 



Relief 244 



