Mild Polar Climates. 279 



the severity of what may be called the Tertiary cold periods, 

 intensified to an exceptionally great extent the warmth 

 and equability of what may be called the Tertiary warm 

 periods. 



Climate of the Tertiary Period, in so far as affected by 

 Eccentricity. — Tf the foregoing conclusions are correct, the 

 following would then seem to be the probable character of 

 the climate of the Tertiary period, in so far as that climate 

 was affected by eccentricity. As is truly remarked by Mr. 

 Wallace, the eccentricity during the past three million years 

 has been almost always much higher than it is now. It will 

 consequently follow that very considerable portions of the 

 Tertiary age would consist of alternate comparatively cold and 

 exceedingly warm and equable periods. These may be said 

 to correspond to the cold and warm periods of the glacial 

 epoch ; but, of course, they could in no sense be called glacial 

 and interglacial periods ; for the cold of the cold periods 

 would not be such as to produce permanent ice, while the heat 

 and equability of the warm periods would far exceed that of 

 the interglacial periods. 



Evidence of such Alternations of Climate. — That such oscilla- 

 tions occurred during the Tertiary period seems to be borne 

 out by the facts of geology and palaeontology. Mr. J. Starkie 

 Gardner, a geologist who has had great experience in the fossil 

 flora of the Tertiary deposits, says that such alternating 

 warmer and colder conditions are supported by strong negative 

 and some positive evidence, found not only in English Eocene, 

 but in all Tertiary beds throughout the world. In the Lower 

 Bagshot of Hampshire have been found, he states, feather- 

 and fan-palms, Dryandra, beech, maple, Azalea, laurel, elm, 

 acacia, aroids, cactus, ferus, conifers, Stenocarpus, and plants 

 of the pea tribe, together with many others. The question 

 which presents itself to one's mind, he remarks, is, how is it 

 possible that the tropical forms, such as the palms, aroids, 

 cactus, &c, could have grown alongside of the apparently 

 temperate forms, such as the oak, elm, beech, and others? 

 Mr. Gardner's explanation is as follows : — 



" Astronomers, having calculated the path of the revolution of 

 the earth in ages past, tell us that in recurring periods each hemi- 

 sphere, northern and southern, has been successively subject to 

 repeated cyclical changes in temperature. There have been for the 

 area which is now England many alternations of long periods of 

 heat and cold. Whenever the area became warmer, the descendants 

 of semitropical forms would gradually creep further and further 

 north, whilst the descendants of cold-loving plants would retreat 

 from the advancing temperature, vice versa. Whenever the area 



