OSCILLATORY CHARACTER OV CONTINENTAL SEAS 



355 



tions are even more ceHainly proved for the larger and deeper oceanic 

 basins. Obviously, the temperature of the epicontinental waters is more 

 readily susceptible to modification in accord with climatic conditions pre- 

 vailing in adjacent continental regions than is that of the great oceans. 

 A fall in average atmospheric temperature that would soon render the 

 continental seas unfit for warm water marine life would have much less 

 effect on a similar fauna of the deeper oceanic basins. 



Now, according to the theory of reversed circulation, warm waters 

 sank in the equatorial zone and reappeared at the surface in the polar 

 regions. Could they have carried the littoral warm water faunas with 

 them? Manifestly, no. Or, could these faunas have migrated in their 

 usual manner along the shore ? Again we must say no, since the hypoth- 

 esis requires a southward movement of cool superficial waters, which 

 would have effectually barred shore migration. Then how did the warm 

 water faunas get to the Arctic regions? 



If we did not know that essentially the same pre-Miocene fossil faunas 

 are found as far north along the Atlantic and Pacific as the deposits have 

 been traced, it might be suggested that the passage to the Arctic was 

 effected during the transition to the "abnormal^' condition of northward 

 superficial circulation, and that at other times the similarity of the peri- 

 odically separated faunas was maintained by "autochthonus," or perhaps 

 better by "geminate" development. However, in the face of this and 

 other facts of faunal distribution the argument seems indefensibly weak. 

 It becomes questionable then if reversal of oceanic circulation was ever 

 an important factor in faunal distribution. Indeed, we might go further 

 and doubt that actual reversals ever occurred. 



Another hypothesis having an important bearing on the problem, so 

 far at least as the Atlantic is concerned, is the land connection between 

 North America and Europe which is believed to have existed at various 

 times in the Paleozoic. Clearly, if such a connection is admitted, deep- 

 seated circulation between polar and equatorial basins through the north 

 Atlantic would have been impossible. Nor could it have occurred through 

 the continental seas, since these were but seldom if ever great inter- 

 oceanic thoroughfares, and they were never deep enough to suggest deep- 

 seated circulation. After all is said, it appears that the fossil faunas 

 migrated north and south along the shores when climatic and other physi- 

 cal conditions were favorable, which seems to have been whenever the 

 continents were low and small ; and that such migrations were prohibited 

 in the occasional highly emergent phases. Whether reversal of oceanic 

 circulation occurred in the latter periods there seems no conclusive means 

 of determining, but that such reversal was in no wise responsible for the 



