26 SMITHSONIAN MISCELLANEOUS COLLKC TIONS VOL. 82 



radius. Hence a coincidence of minor factors sufficient to effect an 

 overturn in the one or the other direction, that is, toward ice forma- 

 tion or melting, would suffice to induce a wide extension of polar 

 ice, or to prevent the polar regions from maintaining a permanent 

 ice cap. If this is true then it seems quite prohable that there was little 

 polar ice during those times already enumerated when temperate 

 floras invaded the polar regions. This would mean profound changes 

 in the distribution of barometric pressures and consequent wind cir- 

 culation, and in fact, in all of the elements which constitute climate. 

 It would mean that in western Greenland, for example, where the 

 most extensive late Eocene Arctic flora has been found, the present 

 day glacial anti-cyclonic winds would be replaced by westerly or south- 

 westerly winds blowing from the relatively warmed waters of Baffins 

 Bay, and this would satisfactorily explain the details of the floral 

 facies. This does not mean that there would be tropical climates 

 in the Arctic or that the region would not be ice bound in the winter 

 season. The protective effect of snow, and cold sufficient to cause 

 a cessation of plant activity during the Arctic night are a physiological 

 ' necessity. Otherwise most vascular plants could not maintain them- 

 selves. They tend to die either if active in darkness or if exposed 

 to desiccation by air and wind when the ground water is frozen. 



Regarding the general history of discussions of geologic climates 

 I believe that most paleontologists who have written on this topic, 

 especially those dealing with the pre Cenozoic periods, have had little 

 basis in fact for their speculations. They seem to me to be utterly 

 oblivious to the great amount of modern work on the distribution 

 of marine organisms ; and their ideas of the climatic significance of a 

 trilobite, eurypterid, or ammonite is purely a tradition inherited 

 from the distant past when all strange organisms were associated with 

 torrid climates. 



In stating my belief in a greater uniformity of climate during the 

 past than obtains at the present I do not wish to be understood as 

 advocating such unsound beliefs as the entire absence of zonation, 

 such as many paleobotanists have defended (Jeffrey, Knowlton), or 

 a similar unifonnity throughout all time. Both are equally disproved 

 both by geological observations and meteorological principles. Jeffrey, 

 for example (Anatomy of Woody Plants, Chapter XXX, 1917), holds 

 that the more ancient the epoch the warmer the climate, and that there 

 has been a gradual and progressive refrigeration during geologic 

 time ; that the organization of secondary wood in extinct plants furn- 

 ishes the most reliable evidence of climatic conditions ; that toward 

 the end of the Paleozoic, growth rings appeared in woods in high 

 latitudes ; that in the Triassic, growth rings were developed ten degrees 



