OCEANOGRAPHY. 13 



where the temperature is higher than that which 

 is necessary for its existence. It might be sup- 

 posed from what has just been said that the 

 temperature of the water at the bottom is con- 

 stant for the same number of fathoms of depth. 

 This is not, however, the case. The temperature 

 of the sea-bottom of the great ocean beds is 

 approximately the same, varying from 28 F. 

 in the Atlantic to 35 F. in the Pacific ; but in 

 places where main basins occur, surrounded on 

 all sides by shallower ridges, the temperature 

 of the bottom of the basin is the same as that of 

 the lowest ridge. For instance, the temperature 

 of the bottom of the Sulu Sea, lying between 

 Borneo and the Philippines, is 40 F. at a depth 

 of over 2000 fathoms. Again, the temperature 

 of the Red Sea is as high as 70 F., although 

 depths of 1200 fathoms occur in its central 

 portions; and this is the same as the tempera- 

 ture at the Straits of Babel Mandeb, which are 

 200 fathoms deep, and form the only outlet to 

 the open ocean. These facts probably cause 

 considerable modification in the character of the 

 animals inhabiting such enclosed basins, but 

 further investigations are needed before we can 

 arrive at any very definite conclusions in the 

 matter. 



Another important element that must be taken 

 into consideration in studying the environment 

 of marine animals, is the quantity and character 

 of the salts held in solution by the sea- water. In 

 the first place we must remember that the sea- 

 water normally contains a far greater percentage 

 of salts in solution than the water of rivers and 



