IV DEPTHS AND DEPOSITS OF THE OCEAN 189 



the potash and soda of sea-water, and these oxides enter to 

 the extent of about 4 per cent each. The iron becomes ferric, 

 and can no longer get away as bicarbonate. The resulting 

 palagonite is a more or less homogeneous and transparent 

 amorphous mineral. Exposed naked to the action of bottom- 

 waters it rapidly breaks down to clay. 



Deep-sea conditions are, on the whole, more favourable to Synthetic 

 the degradation of mineral matter than to the generation of new p'^^'^^'^^^- 

 minerals. Nevertheless a few syntheses are being continually 

 carried on in the muddy parts of the bottom and in the 

 immediately superjacent layers of water; they fall into two 

 groups, viz. true chemical syntheses of new classes of silicates, 

 and mineralogical syntheses of concretionary minerals. The 

 first group comprises glauconite and phillipsite, the second 

 group ferromanganic and phosphatic concretions. 



Glauconite is a hydrous double silicate of potassium and Glauconite. 

 trivalent iron, occurring in rounded grains said to be composed 

 of minute felted crystals. The ideal composition (KFe SioO^. Aq) 

 is claimed for it, but actually the purest marine glauconite 

 hitherto analysed contains 1.5 per cent of AI0O3, 3.1 per cent 

 of FeO, and 2.41 per cent of MgO, with only 'j.'] per cent of 

 K20.^ The chemistry of its genesis is still a complete mystery ; 

 all that can be said is that it appears to result from a meta- 

 morphosis of ferruginous clay, and that, in view of its frequent 

 formation inside the shells of foraminifera (and of its absence 

 in the Red clay and Red mud areas), decomposing organic 

 matter probably plays a part in its formation. On the score 

 of abundance glauconite is a mineral of considerable importance 

 in bottom-deposits, being the characteristic component of the 

 Green sands and Green muds. Glauconite is a mineral belong- 

 ing essentially to the reducing areas of the deep sea. 



The most notable geochemical change associated with 

 glauconite is the withdrawal of potassium out of solution in the 

 sea. This element has a remarkable tendency to be held in 

 loose combination in amorphous and colloidal minerals (like 

 palagonite), and all submarine muds and clays contain a small 

 amount (less than i per cent) of absorbed potash ; the quantities 

 thus progressively entangled at the bottom will be roughly 

 proportional to the aggregate accessions of clayey matter, and 

 can only be a tiny fraction of the total potassium imported into 

 the ocean. In glauconite-producing areas, on the other hand, 



1 Collet and Lee, Proc. Roy. Soc. Edin., vol. xxvi. p. 238, 1905. 



