158 The Ocean — its Currents, Tides, Depth, fyc> 



seize on 'he one great submarine phenomenon indicated by 

 Captain Denham, to assure you- that however it may be modi- 

 fied, I view it as of singular importance in enabling natur- 

 alists to account for the marked separation of the tribes of 

 marine beings which at present exist in regions widely 

 separated from each others. For vast depths are to many 

 inhabitants of the sea (including all the mollusca) what great 

 and snowy heights are to the animals of the land — perfectly 

 impassable barriers. Now, whilst we have in the profundity 

 of parts of the present ocean a distinct reason for the sepa- 

 ration of aquatic races in our times, the near approach, on the 

 contrary, to a general and uniform distribution of marine 

 mollusca in primeval periods, as registered in the ancient sea 

 bottoms which have been raised to form our present conti- 

 nents, compels me to believe that the earlier geographical 

 outlines of our planet were infinitely more simple than the 

 present. In other words, that the oceans were then broader 

 on the whole, the lands of less altitude, and the cavities in 

 the sea bottom by no means so deep as those of our actual 

 highly diversified outlines. For, had such very varied out- 

 lines prevailed in primeval periods, most unquestionably the 

 same land-plants which are found in the old coal formation 

 could not have lived from Spitzbergen and the Polar regions 

 to temperate and even warm latitudes, and in nearly all 

 longitudes ; nor could the same tribes, and often the small 

 species of shells and other animals, have inhabited the most 

 distant seas at the same period. 



It is this varied outline, as brought about after many re- 

 volutions and changes of the crust of the globe, which presents 

 to the meteorologist that mass of complicated problems, so 

 few of which have yet been sufficiently solved to enable us to 

 arrive at definite laws respecting weather, or the causes of 

 its seemingly capricious changes. But still, notwithstand- 

 ing all its variations, there is a mean distribution of heat 

 and cold which restricts certain groups of creatures to each 

 continent and sea ; and the more we can approach to a cor- 

 rect delineation of these zones beneath the waters, as well 

 as those above them, and comprehend the nature of all tides 

 and currents, the more perfectly shall we attain some of the 

 highest aims of the physical geographer. 



