COXTEXTS. XV 



PAGE 



of both with those of Japan, North China, and Europe, 427 ; Number of Pre- 

 glaclal Species now found in the Temperate Zone, 430 ; our Trees originated in the 

 High Latitudes, 432 ; the Vicissitudes to which they have been subjected since 

 the Approach of the Glacial Period, 433 ; Open Lines of Emigration in America, 

 434 ; Peculiar Influences upon the Pacific Coast, 435 ; Extinction of Animals in 

 America by the Glacial Period, 436 ; Alpine Butterflies upon the White Moun- 

 tains, 438 ; List of Plants common to the Okhotsk-Kamchatkan Region and 

 North America, 441. 



CHAPTER XVIII. 

 Europe during the Glacial Period . . . 445-459 



Glaciated Area in Great Britain, 445; on the Continent, 447; Investigations 

 of Professor Lewis, 448; Summary of Conditions in Great Britain by Dr. 

 Harmer, 454; Investigations of Professor Salisbury, 456. 



CHAPTER XIX. 

 The Cause of the Glacial Period .... 461-494 



Recent Astronomical Speculations, 461 ; the Combination of Conditions necessary 

 to produce a Glacier, 461 ; Theories to account for the Glacial Period, 463 ; Decrease 

 of the Original Heat of the Planet, 463; Shifting of the Earth's Axis of Rotation, 

 463; Theory of Progressive Desication, 464; Depletion of Carbon Dioxide in the 

 Atmosphere, 464; Different Temperatures of Space, 465; Mr. Croix's Theory: the 

 Elliptlcit y of the Earth's Orbit and the Precession of the Equinoxes, 466 ; Possible 

 Effect of these upon the Climate, 467; Cause of the Gulf Stream, 469; Causes con- 

 trolling the Distribution of the Heat from the Sun, 477; Woeikoff's Objections to 

 Croll's Theory, 479; Supposed Evidence of Former Glacial Periods, 483; Carbon- 

 iferous and Cambrian Glacial Periods now established, 490. 



CHAPTER XIX (continued). 

 The Cause of the Glacial Period .... 495-531 



Effect of Changes in the Distribution of Land and Water, 495; Theory of Changes 

 of Level, 496; Supplementary Notes by Warren Upham, 520; produced by the 

 Accumulation of Snow over Definite Centers, 525; Field for Mathematical Inves- 

 tigation, 528; Summary, 529. 



CHAPTER XX. 

 The Date of the Glacial Period .... 532-615 



Uncertainty of As ronomical Calculations, 532; Deiect in Lyell's Theory of Uni- 

 formitarlanism, 533; Post-glacial Erosion below Niagara Falls, 536; below Falls of 

 St. Anthony, 552; in Ohio, 560; Freshness of the Glaciated Surfaces, 568; Post-gla- 

 cial Erosion in Minnesota, 571 ; about Lake Michigan, 571 ; Post-glacial Deposition 

 in Kettle-holes, 572; the Question of Two or More Post-tertiary Glacial Epochs, 575 ; 

 Greater Oxidization of Material near the Glacial Boundary, 579; Freshness of In- 

 terglacial Forest-beds, 592; Growth of Peat, 594; Extent of Forest-beds, 603; 

 Former Extension of Lakes Bonneville and Lahontan, 607; Recentness of these 

 Lakes, 610; Length of the Glacial Period, 613; Summary, 614. 



