﻿Unmapped Areas on Eartlia Surface. 449 



distribution is concerned. The department of oceano- 

 grapliy is a comparatively new creation : indeed, it may l)e 

 said to have come definitely into being witli the famous 

 voyage of the " Challenger." There had been expedition^ 

 for ocean investigation before that, but on a very limited 

 scale. It has been tln^ough the results obtained by 

 the " Challenger," supplemented by tliose of expeditions 

 that liave examined more limited areas, that we have 

 been able to obtain an a])proximate conception of the 

 conditions which prevail throughout the various ocean 

 deptlis — conditions of movement, of temperature, of 

 salinity, of life. We have only a general idea of the 

 contours of the ocean bed, and of the composition of 

 the sediment which covers that bed. The extent of the 

 knowledge tluis acquired niay be gauged from the fact 

 that it occupies a considerable space in tlie fifty quarto 

 volume — the " Challenger " publications — which it took 

 Dr. John Murray twenty years to bring out. 



What islands are to the ocean, lakes are to the land. It 

 is only recently that these interesting geographical 

 features have received the attention they deserve. 



Elvers are of not less geographical interest than lakes, 

 and these have also recently been the subject of special 

 investigation by physical geographers. I have already 

 referred to Professor Davis' study of a special English 

 river system. The work in the English lake district by 

 Mr. Marr, spoken of in connection with Dr. Mill's investi- 

 gations, w^as mainly on the hydrology of the region. Both 

 in Germany and in Kussia special attention is being given 

 to this subject, while in America there is an enormous 

 literature on the Mississippi alone, mainly, no doubt, from 

 the practical standpoint, while the result of much 

 valuable work on the St. Lawrence is buried in Canadian 

 official publications. 



