MARINE DEPOSITS 213 



from the land and shallow water, but in some 

 of the muds there is an almost entire absence 

 of the remains of pelagic calcareous organisms 

 (blue mud, red mud, green mud, volcanic mud, 

 and coral mud). On the continental shelf the 

 deposits are principally made up of the larger 

 fragments derived from the land along with 

 the remains of bottom-living organisms (quartz 

 and coral sands, gravels, marls, etc.). 



Stratification. — In many deposit-samples 

 brought up in the sounding-tube after it has 

 penetrated deeply into the bottom distinct evi- 

 dences of stratification may be discerned, 

 especially in terrigenous deposits ; indeed, 

 the opinion has been expressed that stratifica- 

 tion is the rule, and where it is not observed 

 the sounding-tube has not penetrated through 

 the uppermost layer. Sometimes globigerina 

 ooze overlies blue mud, diatom ooze, or red 

 clay, sometimes diatom ooze overlies blue 

 mud, and sometimes red clay overlies globi- 

 gerina ooze ; the last-mentioned arrangement 

 seems to point to subsidence of the sea-floor. 

 More frequently differences in colour, but no 

 great differences in composition, are met with 

 in the same deposit-type. 



Organic Matter. — The role played by organic 

 matter in the ocean is a very complex and 

 important one, leading to continual and 

 extensive changes in the internal constitution 



