28 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 82 



not done so although I did pubHsh such a map for the Eocene in 1922. 

 This intention was abandoned for the reason that it was not possible 

 to compile maps tliat did not cover too much time nor in which the 

 extrapolation was not so great as to destroy any real value. 



Arldt has compiled maps which represent a synthesis of opinions 

 and showing the areas of agreement and disagreement among special- 

 ists and to these the reader is referred. The debatable North Atlantic 

 continent and the Gondwana continent would, if they ever existed, 

 have had a profound effect on climate. Whether or not they were 

 ever realities I am not prepared to say. I can, however, make the 

 following statements with a considerable degree of certainty, namely : 

 That there was a wide extent of land in the Northern Hemisphere from 

 late Mississippian through the Permian. That the Arctic was land- 

 locked in early and middle Triassic and that there was a wide trans- 

 gression of the sea in the Neo Triassic. That the maximum Jurassic 

 transgression was about Oxfordian ; that of the Lower Cretaceous was 

 in the Neocomian ; that of the Upper Cretaceous was in the Emscher- 

 ian ; that the late middle Eocene was a time of wide sea transgression 

 and low lying lands ; and that during the Miocene, the age to which 

 Heer assigned the Arctic Tertiary floras, the amount of land in the 

 Northern Hemisphere was nearly as great as it is at the present time. 



It will be seen that there is a correspondence between times of sea 

 extension and Arctic floras and times of land extension and no traces 

 of Arctic floras. This correspondence is not exact, and so little of 

 paleogeography is objective, that I would not want to appraise it for 

 more than it is worth, but in so far as it is known it does offer 

 corroboration of my thesis. 



I had expected to attempt an estimate of the meteorological condi- 

 tions at the various times at which fossil floras are found in the Arctic, 

 l)Ut after abandoning any hope of getting reliable paleogeographic 

 data I have also abandoned the former. Brooks has published some 

 interesting meteorological estimates using as a basis those parts of 

 Arldt's maps where authorities agree, but it should be pointed out that 

 majorities are quite as likely to be wrong in science as in politics, and 

 if generalizations are valid (which of course they are not) then 

 minorities are usually right. 



There are, however, a few considerations that may be put forward 

 as having a high degree of validity, namely the importance of ice as 

 a third factor, added to the long recognized rotational f i)lanetary) and 

 geographic (distribution of land and water and altitude) factors 

 in influencing the distribution of pressures and consequently of pre- 

 vailing winds. And also the effect of the volume of fresh water car- 



