Shaler.] 298 



tion of heat, and all the lines indicating equal intensity of meteorolog- 

 ical phenomena would want the irregularities now given to them by- 

 oceanic streams. As far as temperature affects the distribution of 

 organic life, this assemblage of circumstances would doubtless favor 

 the existence of faunte having their boundaries more nearly deter- 

 mined by latitude than at the present day. Within the limits of the 

 equatorial current, there would exist other influences than equality of 

 temperature tending to influence the distribution of life. As far as a 

 powerful current moving always in the same latitude, could tend to 

 equalize the animal and vegetable contents throughout the course swept 

 by its waters, we would expect to find uniformity in the life of the 

 intertropical region. We can not safely assert that perfect uniformity 

 in the zoological characteristics of this region would be the result of 

 such a current. It seems improbable that the ocean floor could long 

 exist before such differences in depth would arise from the corruga- 

 tion of the crust that bathymetrical distribution of the organisms 

 within contained would be necessary. This and other actions would 

 oppose the perfect equalization of the life of this area. Nevertheless, 

 when we consider the large number of structures which cast their prog- 

 eny into the water, free to be borne with its movement until either 

 destroyed or fixed in a suitable habitat, we can not resist the conclu- 

 sion that in this first condition of oceanic streams we have a powerful 

 agent tending to equalize the life throughout the region within the 

 tropics. 



From these considerations we may conclude that the period in the 

 history of the earth, during which the disruption of the equatorial 

 current was effected, must have been marked by a great alteration of 

 climatic conditions, and the loss of a poAverful agent tending to pro- 

 duce an uniformity in the marine life in the region of the Equator. 

 With the elevation of the first continental barrier across the whole 

 breadth of the tropics, we would have in place of the former encir- 

 cling current two closed whirlpool-like movements, the type of all 

 oceanic streams of the present day. With this change, the influence 

 of oceanic movements on climate would begin. It is not necessary to 

 suppose that the barriers should have any meridional extension beyond 

 the diameter of the trade wind belt. As soon as the northern and 

 southern halves of the equatorial current had been diverted from their 

 course and turned in the direction of their respective poles, they 

 would, in accordance with well known laws, bend to the eastward 

 and depart more and more from a meridional course as they gained 

 higher latitudes. Assuming that the barriers extended in a due north 

 and south direction, it can be demonstrated that very soon after the 

 streams ceased to be impelled to the westward by the trade winds, 

 thov would dpsfrt the shores which had deflected them from their 



