OCEAN DEPOSITS: DIATOM OOZE 35 



nowadays become so popularly unpopular. Many of 

 them are enclosed in an excessively fine shell of the 

 nearly-indestructible substance silica, like the Radio- 

 laria. 



When the oceanic Diatoms die, their shells, of 

 course, sink like an invisible dust to the bottom ; and 

 although in warm latitudes these are lost amid the 

 downpour of Foraminifera, yet in colder regions, 

 where surface Foraminifera are few, the Diatoms 

 hold their own, and at length may collect as a pale 

 siliceous deposit known as Diatom-ooze. 



But neither Diatom nor Radiolarian ooze, nor yet 

 — abundant as it is — Globigerina-ooze, cover all, or 

 nearly all, of the floor of the open ocean. Far more 

 extensive than all these oozes combined is a deposit 

 called by its discoverers in the Challeitger, red clay, 

 which, when examined under the microscope, is found 

 to consist in large part of altered volcanic materials. 

 This red clay is found pure only at the very greatest 

 depths. Mixed up with it, of course, are certain 

 indestructible remains of marine animals — spicules of 

 siliceous sponges, sharks' teeth, ear-bones of whales, 

 etc. — such as are also to be found in all marine 

 deposits ; but a great part of it is derived from the 

 minute particles of the volcanic and cosmic dust that 

 floats invisible in the atmosphere. Though this dust 

 is co-extensive with the atmosphere itself : though 

 probably it exists everywhere, and is falling unseen 



