4 BERRY— A POSSIBLE EXPLANATION 



the modern species in nature appear to be confined to tropical and 

 sub-tropical environments, fossil forms are found in association with 

 temperate types, as, for example, in the Upper Cretaceous of Green- 

 land, the early Eocene of the Rocky Mountain region and Gulf states, 

 and the lower Miocene of Florida (it is obvious that the advocates of 

 former torridity can exactly reverse the bread-fruit argument), so 

 that one must use considerable caution in any attempt to interpret its 

 meaning in terms of climate. 



It may be remarked parenthetically that I do not consider Aphle- 

 bise as indicative of heat, but humidity. That Ginkgo is not a tropical 

 type, but appears to be hardy throughout the Temperate Zone, and 

 does not flourish under cultivation in the Tropics. That Cycads and 

 Conifers are not good criteria for either moist or sub-tropical cli- 

 mates, but quite the reverse. That Gleichenia and its present-day 

 segregates, although commonly found in the Equatorial Zone at the 

 present time, are not limited to the tropical part of that zone, but are 

 frequently more at home in the sub-tropical or temperate altitudinal 

 zones in Equatorial uplands, as in Hawaii, the Eastern Andes, etc. 



Doubtless terrestrial plants are better indices of climate than are 

 other organisms, and they are admittedly more important in this 

 respect than marine forms of life. Plant fossils have this merit aside 

 from any question of botanical identification, and this feature seems 

 to have been lost sight of by numerous critics of paleobotanical prac- 

 tise : that the size and form of leaves, their texture, the arrangement 

 and character of their stomata, and the seasonal changes in wood, 

 afford criteria that are quite as valuable climatically even though the 

 species or genus to which they belong remains undetermined. With- 

 out venturing further on the sea of words that constitutes the elusive 

 generalities of most discussions of past climates, I propose to contrast 

 the Tertiary "Arctic flora" with that which existed contempora- 

 neously in lower latitudes, after which I will suggest a possible 

 explanation to account for the observed facts. 



The exact age of this "Arctic flora" can not be conclusively 

 proven, but it is a reasonable assumption that it is of approximately 

 the same age wherever found, and this assumption rests on actual 

 community of composition, and not on an environmental premise, 



