QUATERNARY AGE. 307 



left would be raised sufficiently to produce the cypress, sequoia, fig 

 tree, and even the palm. Such a vegetation under these circum- 

 stances might flourish within the Arctic circle. A heated equator 

 would send warm currents of air and water to heat up the polar re- 

 gions. Some such conditions Lyell thought existed, for example, 

 during the Miocene, or earlier still during the Carboniferous, when 

 tree ferns grew on islands in Arctic regions. Lyell considered the 

 atmosphere to be the chief instrument for the distribution of heat. 

 On the other hand the prevalence of polar continents and an oceanic 

 equator produced arctic conditions in all high latitudes. The pro- 

 gress of discovery, however, has brought to light many facts which 

 cannot well be reconciled with this theory. Among these facts are 

 intercallated beds representing mild conditions of climate in the 

 midst of and during glacial times. The most conspicuous example 

 of this is the Old Forest Bed already spoken of. Even in Arctic 

 regions tree trunks have been found in the midst of glacial debris* 

 It is also questionable whether the atmosphere flowing northward 

 from tropical land masses would heat up the poles. Its heat would 

 be dissipated long before reaching the extreme north. At the pres- 

 ent day western America receives its high temperature, not from 

 the tropical winds, but from the breezes that blow over the Japan 

 current, as western Europe is warmed by the Gulf Stream. East- 

 ern Europe and Asia receive no benefit from these warm winds 

 they are cooled long before they reach the great interior. It is also 

 extremely questionable whether there ever was exactly, or even ap- 

 proximately, such a distribution of land and water as this theory 

 calls for. Many other objections are urged against Lyell's theory. 

 Geologists, therefore, now look for the causes which produce 

 changes of climate to cosmical rather than to terrestrial influences. 

 The cosmical theory that would explain the phenomena of cli- 

 mate that is now receiving most attention was proposed by and is 

 still ably defended by James Croll, and is also maintained by James 

 Geike, both connected with the Geological Survey of Scotland. 

 According to this theory, two causes are chiefly operative the 

 changing eccentricity of the earth's orbit and the precession of the 

 equinoxes. Leverier's calculations make "the superior limit of the 

 earth's eccentricity 0-07775-" At the present time it is lessening, 

 and will continue to do so for 23,900 years, when its value will be 

 -.0031 4; after which it will again increase. These changes of ecccn- 



*See James Geike's Groat Ice Age, page 462. 



