858 THE JOURNAL OF GEOLOGY. 



effecting chemical changes do not penetrate the water deeper than 400 

 meters and as the other conditions of assimilation are met above this 

 line, it is proposed to distinguish a diaphanic region including the land 

 and the water to a depth of 400 m. and inhabited by assimilating 

 organisms and an aphotic region including the ocean and lakes below 

 the assimilation-line and the dark caves of the crust, where plant 

 life is impossible. Temperature limits — 85 ° C. to 3 C. for water 

 organisms — restrict greatly the distribution of life in the diaphanic 

 region. 



Upon a somewhat different basis of classification are next consid- 

 ered the life-zones of the ocean (divided first into oceanic basins and 

 second into shore, shallow, and deep sea zones), and the kind of life 

 inhabiting each (the author following Haeckel in dividing the ocean 

 forms (Halobios) into Benthos, or bottom forms, Nekton or active, swim- 

 ming forms and Plankton or passive, floating forms with numerous 

 subdivisions). 



Intimately connected with the question of environment in its rela- 

 tion to life is the facial development of the ocean bottom. Thus 

 we find that certain forms as Mytilus and Mactra are found upon a 

 mud bottom, other forms as Anomia and Spondylus love a gravel 

 bottom. A change in bottom from any cause will cause a change in 

 the fauna — a migration. The influence of the bottom extends, how- 

 ever, not only to the plants and animals living directly upon it but 

 also to the Nektonic forms which feed upon certain plants and 

 further to the animals of prey wno live upon the animals (of both 

 Benthos and Nekton) who frequent the same region. Further than 

 this the fact that fish pick out a certain kind of bottom on which to lay 

 their eggs causes them to frequent certain places during the spawning 

 season. 



A great many interesting questions relative to the effect of environ- 

 ment are discussed and by numerous facts illustrated in the following 

 sections on the influence of light, of temperature, of salt percentage, 

 and the effects of tides, waves, and circulation of the water upon the 

 living organisms. The formation of oceanic islands and all those 

 movements of the earth's crust which alter its position and cause a 

 relative or absolute change in the sea-level have an immediate and 

 vital influence upon all life within the region of change, because it 

 affects at once the various conditions under which the organisms 

 have been living. This constant change of environment by com- 



