PALEOGEOGRAPHIC MAPS OF NORTH AMERICA 39 



When the distribution of lands and waters is thus inferentially 

 completed, we may infer further that the dominant features of 

 oceanic circulation have obeyed the conditions of atmospheric cir- 

 culation and of rotation of the sphere which now govern the great 

 oceanic eddies. We may introduce in the Atlantic and Pacific the 

 dominant drifts from east to west in equatorial regions with the 

 resulting circulation northward along the east coast and southward 

 along the west coast of the continent. A circulation of the oceanic 

 waters in the epicontinental seas must result from the great oceanic 

 drifts, and the direction of flow will be determined by the configura- 

 tion of the lands and the depths of the seas. 



From the geographic conditions thus developed inferences regard- 

 ing the climate and the life habitats of the time may be drawn. If 

 now we turn to the records of paleontology and compare the dis- 

 tribution of faunas and floras with the conditions of distribution 

 which should result from the inferred physical phenomena, we may 

 check the whole line of reasoning and by a readjustment draw a 

 step nearer to the truth. This is the method which has been pursued 

 in making the maps of North America that are published with the 

 papers in this number and that will appear in connection with 

 further papers of the series. 



In a first essay of this kind (and I am not aware of any earlier 

 attempt to combine the various lines of evidence in a similar manner) 

 it is probable that important facts have been overlooked. The 

 very broad scope of the discussion makes this probability almost a 

 certainty, and it is not to be expected that the maps here presented 

 should give a final or satisfactory solution of the problems. They 

 are to be regarded as tentative and suggestive only. 



On one point they have been particularly criticized, it being said 

 that each individual map covers so long a period of time and such 

 diverse conditions that they do not truly represent any special geo- 

 graphic phase of the continent. This criticism is valid, and one of 

 the steps in the advancement of knowledge will be that of selecting 

 narrower time limits and more precise correlations than have been 

 attempted in these cases. W^e may undoubtedly make progress in 

 this direction at the present time so that the fifteen maps which 

 win accompany this series may be replaced by two or three times as 



