204 THE OCEAN 



to which it owes its name, being due to the 

 character of the sediment brought down by 

 the large rivers in the vicinity. The ferric 

 oxide is so abundant that it is apparently 

 not all reduced to ferrous oxide, and iron 

 sulphide does not accumulate in this type of 

 deposit, hence the absence of the blue colour 

 so prevalent in the deposits along other conti- 

 nental shores. 



3. Green Mud. — This type may also be 

 regarded as a variety of blue mud, character- 

 ised by the abundance of glauconite grains 

 and glauconitic casts of calcareous organisms, 

 which are usually of a greenish colour and 

 impart a green tinge to the deposit, hence the 

 name. Along high and bold coasts free from 

 large rivers the deposition of fine detrital 

 matter from the land is less abundant than 

 in other positions, and the continental rock 

 fragments and mineral particles are there 

 longer exposed to the solvent action of sea- 

 water, the products of their decomposition 

 yielding the materials for the formation of 

 the glauconite. In the shallower waters 

 nearer the land the deposits contain less clayey 

 matter and are more granular ; they are 

 then called Green Sands. This type is charac- 

 teristically represented off the Atlantic and 

 Pacific coasts of North America, off Japan, 

 off Australia, and off the Cape of Good Hope, 



