GROWTH OF GEOLOGY. 279 



The recognition of oceanography as a distinct 

 branch of science may be said to date from the 

 commencement of the Challenger investigations, 

 and although the study is still in a sense in its 

 youth, " so much has already been acquired that the 

 historian will, in all probability, point to the ocean- 

 ographical discoveries during the past forty years 

 as the most important addition to the natural knowl- 

 edge of our planet since the great geographical 

 voyages associated with the names of Columbus, Da 

 Gama, and Magellan, at the end of the fifteenth and 

 the beginning of the sixteenth centuries." * 



Our picture of the Deep Sea is necessarily darkly- 

 shaded and in many respects dim and vague, but 

 it is not wanting in precise detail. Some indication 

 of this may be given. At great depths there is 

 necessarily enormous pressure (at 2,500 fathoms 

 about 2 J tons upon the square inch) ; it is quite 

 calm, untouched by the severest storms ; the tempera- 

 ture is low and uniform, often just a little above the 

 freezing-point all the year round; the water is rel- 

 atively rich in oxygen ; there is practically no light, 

 apart from phosphorescence; there are therefore no 

 green plants and there is no secure evidence even 

 of Bacteria; there is no depth limit to the distri- 

 bution of animal life and the population includes 

 representatives of most of the great types of animals 

 from Protozoa up to fishes; the animals necessarily 

 feed to a large extent upon one another, but funda- 

 mentally upon the organic debris which sinks from 

 above, and not least upon the ceaseless rain of pelagic 

 Protozoa which sink down from the surface as they 

 die. A strange, silent, cold, dark, plantless world 1 



* Sir John Murray. Address Section E, Rep. Brit. Aaa.y 

 1899, p. 790. 



