IV DEPTHS AND DEPOSITS OF THE OCEAN i6i 



and siliceous shells and skeletons of pelagic or plankton organ- 

 isms may greatly predominate. This fact affords a ready Classification, 

 means of dividing marine deposits into two main classes, viz. 

 Terrigenous Deposits, largely made up of detritus derived 

 directly from emerged land, with the remains of benthonic 

 organisms, and Pelagic Deposits, containing little if any land- 

 detritus, but largely made up of the remains of pelagic organisms. 

 The former class of deposits must therefore form a border, 

 varying in extent according to circumstances, around all the 

 land-masses and islands of the world, while the latter class of 

 deposits occurs in those regions so far removed from the land- 

 masses and islands that very little material derived directly 

 from the land can reach the position where they are found. 

 The dividing lines between these two classes of deposits, and 

 between the various types included in them, are not sharply 

 defined, but the different kinds of deposits merge gradually the 

 one into the other, so that frequently two names, and in some 

 cases even three names, might equally well be applied to the 

 same sample. It is the terrigenous deposits laid down in close 

 proximity to the land, and in enclosed seas like the Mediter- 

 ranean, that are represented in the geological series of rocks, 

 but it is extremely doubtful whether the pelagic deposits laid 

 down in deep water far from land have any analogues among 

 the geological strata. 



After a careful study of all the available samples, Murray and 

 Renard gave the following classification of marine deposits : — 



Marine Deposits 



' Red clay 

 Radiolarian ooze 

 Diatom ooze 

 Globigerina ooze 

 Pteropod ooze 



Blue mud 

 Red mud 

 Green mud 

 Volcanic mud 

 Coral mud 



Shallow - ^^'■ater Deposits, 1 o j i 



K^fw^^.. 1..,,. wof«. ^.ovi.. I Sands, gravels, 

 muds, etc. 



Deep- Sea Deposits, 

 beyond loo fathoms. 



I. Pelagic Deposits formed 

 in deep water removed 

 from land. 



Terrigenous 

 formed in 



Deposits, 

 deep and 



between low water mark 

 and loo fathoms. 



3. Littoral Deposits, between 1 ^ 1 



, • , J , .1 Sands, gravels, 



high and low water \ a \ 



° 1 muds, etc. • 



marks. j 



shallow water close to 

 land-masses. 



