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Now biologically abyssal conditions are quite different from 

 physically abyssal conditions. Of two localities on the sea floor, 

 each at a depth of iooo fathoms and with a temperature of 

 36° Fahrenheit, and each situated beneath a similar rich belt of 

 plankton, one may be biologically truly sublittoral, the other 

 just as truly abyssal. 



In one of these localities, situated let us say toward the 

 eastern shore of an ocean, there might be a constant west wind 

 blowing over the surface of the sea which would drive the 

 surface water inshore, gradually submerging the littoral water 

 which would carry down with it all of its included plankton, 

 rendering possible the existence of sublittoral crinoids even at 

 the great depth given. 



In the other locality, let us say toward the western shore 

 of an ocean, there might exist along the coast an abyssal 

 current moving southward which would continually draw up 

 and carry along with itself water from greater depths. Such a 

 current would prevent to a large degree the deposition of the 

 plankton falling from the layers above it, for these plankton 

 organisms would remain suspended in its upper layers and 

 would be deposited chiefly in the belt of slack water between 

 it and the more superficial currents. Thus in this locality there 

 could exist only typically abyssal organisms which, aided by 

 the drawing up of the water from the abysses, would here 

 thrive and, secure from the competition of economically more 

 perfect sublittoral types, would extend their range to far higher 

 levels than those usually inhabited by them. 



Off the Atlantic coast of southern South America, off the 

 southeastern coast of Africa, and south of Australia and New 

 Zealand the distribution of the abyssal crinoids is such that it 

 can only be explained by supposing a southerly, and slight 

 upward, movement of the abyssal water. For on these coasts the 

 local deep water crinoids extend their ranges very far to the 

 southward, just as on the opposite coasts (the northeast Pacific 

 and the northeast Atlantic) they extend their ranges far to the 

 northward and westward. 



It is probably from the abysses of these regions, therefore, 



(285) 



