560 F. H. KXOWLTOX EVOLUTION OF GEOLOGIC CLIMATES 



and warmed and •'rendered light because warm, yet heavy because 

 saline." In the matter of actual density the equatorial waters are lighter 

 than the polar waters, but the balance is very small, ^%nd/"" says Willis, 

 ^'were the polar waters less chilled or more freshened, or both, the 

 equatorial waters would be heavier, and the reversed circulation suggested 

 by Chamberlin must result." 



As thus presented, it must be confessed that this hypothesis seems 

 reasonable, and if it could be proved would be of weight in accounting 

 for the presence of tropical or subtropical vegetation in polar lands ; but 

 it was reserved for Dr. E. 0. I'lrich to point out its utter failure to 

 explain the occurrence of the same marine faunas in the polar regions 

 that are found in temperate and tropical zones. On this point Ulrich "*'" 

 says : 



•"In the first place these faunas, with very few exceptions, are all littoral or 

 near-shore faunas, and their migration, whether in the oceanic or continental 

 basins, are almost confined to the shore and bottom of the shallow seas in 

 which they thrived. With organisms so sensitive as these to changes in tem- 

 perature and depth, extensive migration under any but equable climate and 

 bathymetric conditions would have been highly improbable, if not impossible. 

 As corals and other animals that are now restricted to warm waters did sa 

 migrate, we must assume either that at such times mild climates prevailed or 

 that in ages preceding the present these organisms were not affected by changes 

 in temperature — a conclusion altogether repugnant to the geologist. Assuming 

 that they were then as now as sensitive to temperature changes, their fossil 

 occurrence in all latitudes must be accepted as proving at least occasional 

 times of universally mild climates — that is, such conditions prevailed in at 

 least the relatively brief geologic ages of which we have a marine sedimentary 

 record in the boreal 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 hypothesis requires a southward movement, 

 of cool superficial waters, which would have effectually barred shore migra- 

 tion." . . . 



Ulrich finally concludes as follows: 



"It becomes questionable then if reversal of oceanic circulation was ever an 

 important factor in faunal distribution. Indeed, we may go further and doubt 

 if actual reversals ever occurred." 



If for the moment we accept this postulate of a reversal of ocean! :• 

 circulation, what effect may it be presumed to have on plant distribution? 



*® E. O. Ulrich: Revision of the Paleozoic systems. Bull. Gool. Soc. Am., vol. 22. 1911, 

 p. 354. 



