299 



[Shaler. 



course. This action would prevent any considerable portion of the 

 deflected waters passing around the obstructions ; indeed it seems 

 ])robable that only those portions which had lost their velocity by fric- 

 tion against the opposing shores could pass around such obstructions 

 and continue their equatorial path. 



The effect of this last condition of oceanic circulation on marine 

 life would be widely different from that exercised by the continuous 

 equatorial current. While the latter favored similarity in the organic 

 contents of the region traversed by it, and admitted the existence of 

 identical climatic conditions over all regions of equal latitude, the 

 condition we are now considering would tend to favor the dissimilar- 

 ity of marine intertropical life in different areas, and would pro- 

 duce the great diversities of climate we now find in regions at the 

 same distance from the Equator. 



There are some direct effects exercised upon organic life in the 

 divided condition of the ocean movements which are in striking con- 

 trast to the action of the continuous tropical current on vital forms. 

 If we take any of the existing ocean streams, it is seen at a glance 

 that in its circuit its waters and their contents, as far as unprovided 

 with means of voluntary motion, are being constantly brouo-ht into 

 regions of different temperatnres. If we suppose any species of ani- 

 mal adapted to exist in the temperature found in any one portion of 

 the current, and casting its progeny into the ocean in their imma- 

 ture state, during which they would be entirely at the mercy of the 

 moving waters, we perceive at once that it must often happen that 

 before development advances far enough to enable the youno- to 

 become fixed, they will be swept into such different conditions of 

 temperature that they would be destroyed. By converging the tem- 

 perature normal to a given point to higher latitudes, or the reverse, 

 the north and south range of species, as far as affected by tempera- 

 ture, could be much greater than during the continuance of the 

 unbroken current. Thus while the existence of the equatorial cur- 

 rent would favor the east and west extension of forms, meridional 

 streams would favor a greater extension towards the Poles. 



While the tropical current remained unbroken, all the transporting 

 power of the ocean would operate in a Avesterly direction. With the 

 disruption of this current, we would have in temperate, boreal and 

 austral regions, a transporting agent, c(»mpetent to sweep objects 

 in an easterly direction, the portions of the streams neighboring to 

 the poles having an essentially eastern movement. 



If we adopt the usually accepted view of the action of those forces 

 concerned in the formation of land masses, which assigns to the conti- 

 nental areas and the sea the most inconstant relations, we would find 

 it impossible to effect even the most general determination of the 



