220 CONFERENCE ON PALEOZOIC PALEOGEOGRArHY 



from land areas, or submarine plntonic action altering the temperature 

 or the chemical constitution of the sea water locally — all might at times 

 have a temporary influence of some importance, but necessarily of a 

 trifling kind compared with the two chief factors above mentioned, the 

 currents and the oceanic circulation due to permanent cosmic causes of 

 the first order of magnitude. 



When we find the shore fauna of the eastern coast of South America 

 practically the same on the shores north and south of the Amazon estuary 

 we conclude that the distribution of the fauna antedates the existence of 

 the estuary. When we find the boreal fauna extending down the eastern 

 coast of North America, with representatives as far south as Georgia, we 

 infer, what is proved by hydrographic investigation, that the Polar cur- 

 rent is represented by an inshore band of cold water. We find on the 

 Pacific coast of America the Oregonian fauna coinciding in distribution 

 with the divaricating branches of the North Pacific current ; the Peruvian 

 fauna with those of the Humboldt or Peruvian current; on the Asiatic 

 coast the Kuro Siwo and the Japanese fauna, the Okhotsk fauna and the 

 Kamchatka current, are practically coincident. All over the world the 

 close association of the range of temperature-bearing waters and marine 

 faunas is recognizable, though occasionally less clear on account of the 

 intervention of land barriers or minor causes. 



When sudden changes of faunal characteristics occur in successive 

 fossil faunas in the Tertiary, as at the end of the Oligocene and the be- 

 ginning of our Chesapeake Miocene in the southern part of our coastal 

 plain, though no orographic changes or unconformities appear on the 

 spot, we are justified in concluding that changes at a distance have taken 

 place which have altered the course of ocean currents and consequently 

 have brought about local changes of temperature. 



If it be possible to lay down with approximate accuracy the distribu- 

 tion of land at no matter what distance of geologic time, an application 

 of the principles governing the distribution of ocean currents and the 

 circulation of oceanic waters should enable the geologist to map the ap- 

 proximate distribution of the marine faunas at that epoch, always pro- 

 vided the difference of sea temperatures between the tropics and the 

 Polar sea was at that period sufficient to affect organic life then existing 

 in the ocean. 



