CONTENTS. IX 



PAGE 



The Development and the Thickness of the Ice-sheets , . . . . 355 



Stages in the history of an ice-sheet, 358. 



The Work of an Ice-sheet . . 358 



Formations made by the Ice-sheets. 359 



The ground moraine, 360. A terminal moraine, 362. 

 Development of terminal moraine topography, 365. 



Fluvioglacial Deposits. . . . . 368 



At the edge of the ice, 368. Beyond the edge of the ice, 

 371. Gradational types: pitted plains, patches of gravel and 

 sand, 373. Beneath the ice, 373. Deposits of superglacial 

 and englacial streams, 376. 



Relations of Stratified to Vnstratified Drift „ . 377 



Extraglacial deposits, 377. Supermorainic deposits, 377. 

 Submorainic (basal) deposits, 377. Intermorainic stratified 

 drift, 378. Topographic distribution of stratified drift, 378. 



Changes in Drainage Effected by Glaciation. 379 



The Succession of Ice Invasions 382 



The sub-Aftonian, or Jeresyan, glacial stage, 384. The 

 Aftonian interglacial stage, 384. The Natchez formation, 386. 

 The Kansan glacial stage, 388. The Yarmouth interglacial 

 stage, 389. The Illinoian glacial stage, 391. The Sangamon 

 interglacial stage, 391. The Iowan glacial stage, 391. The 

 Peorian interglacial stage, 392. The Earlier Wisconsin glacial 

 stage, 392. The fifth interval of recession, 393. The Later 

 Wisconsin glacial stage, 393. The glacio-lacustrine substage, 

 394. The Champlain substage, 403. 



The Loess. 405 



Origin, 409. 



The Duration of the Glacial Period 413 



Foreign 421 



The Cause of the Glacial Period 424 



Hypsometric Hypotheses 424 



The hypothesis of elevation, 424. 



Astronomic Hypotheses. tmm 426 



CrolPs hypothesis, 426. Other astronomical hypotheses, 

 431. The hypo hesis of a wandering pole, 431. 



Atmospheric Hypotheses „ o 432 



Variations in depletion the working factor, 432. Local- 

 ization, 433. . Periodicity, 433. Variations in supply the 

 working factor, 445. Proximate hypotheses, 445. 



