OUR KNOWLEDGE OF THE BEEP SEA. 45 



shallower waters near coasts, but even in the greater depths of all 

 oceans, animal life is exceedingly abundant. A trawling in a 

 depth of over a mile yielded two hundred specimens of animals be- 

 longing to seventy-nine species and fifty-five genera. A trawling 

 in a depth of about three miles yielded over fifty specimens be- 

 longing to twenty-seven species and twenty-five genera. Even in 

 depths of four miles fishes and animals belonging to all the chief 

 invertebrate groups have been procured, and in a sample of ooze 

 from nearly five miles and a quarter there was evidence to the 

 naturalists of the Challenger that living creatures could exist at 

 that depth. 



Recent oceanographic researches have also established beyond 

 doubt that while in great depths the water is not subjected to the 

 influence of superficial movements like waves, tides, and swift 

 currents, there is an extremely slow movement, in striking con- 

 trast with the agitation of the surface water. Although the 

 movement at the bottom is so slow that the ordinary means of 

 measuring currents can not be applied accurately to them, the 

 thermometer furnishes an indirect means of ascertaining their ex- 

 istence. Water is a very bad conductor of heat, and consequently 

 a body of water at a given temperature passing into a region 

 where the temperature conditions are different retains for a long 

 time, and without much change, its original temperature. To 

 illustrate: The bottom temperature near Fernando do Noronha, 

 almost under the equator, is 0"2° C, or close upon the freezing 

 point ; it is obvious that this temperature was not acquired at the 

 equator, where the mean annual temperature of the surface layer 

 of the water is 21° C, and the mean normal temperature of the 

 crust of the earth not lower than 8° C. The water must therefore 

 have come from a place where the conditions were such as to give 

 it a freezing temperature ; and not only must it have come from 

 such a place, but the supply must be continually renewed, how- 

 ever slowly, for otherwise its temperature would gradually rise by 

 conduction and mixture. Across the whole of the North Atlantic 

 the bottom temperature is considerably higher, so that the cold 

 water can not be coming from that direction ; on the other hand, 

 we can trace a band of water at a like temperature at nearly the 

 same depth continuously to the Antarctic Sea, where the condi- 

 tions are normally such as to impart to it this low temperature. 

 There seems, therefore, to be no doubt that there is a current 

 from the antarctic to the equator along the bottom of the South 

 Atlantic. 



From the millions of reliable deep-sea soundings that have 

 been made during the last forty years the more general features 

 of the bathymetric chart of the world have been firmly estab- 

 lished ; and the ancient idea, derived chiefly from a supposed 



