40 A TEXTBOOK OF OCEANOGRAPHY 



miles, covering nearly the whole of the western portion of the 

 basin. In the Pacific the area is over 14! million square miles. 

 3. Diatom Ooze is a siliceous sediment composed mainly of 

 the shells of plants (diatoms). It is found in high latitudes in 

 both hemispheres, and originates in the phytoplankton. The 

 name was introduced by Murray in his Challenger report, and 



FIG. 5. BOTTOM AND PELAGIC DIATOMS. 



applied to a deposit which, when wet, has a yellowish straw 

 or cream colour ; when dry, nearly pure white, resembling 

 flour. The surface layers are thin and watery, the deeper 

 layers laminated. Near land it takes on a bluish tint. The 

 calcium carbonate percentage is low, ranging from 3 to 30 

 per cent. 



