CHAPTER VI. 
CHEMICAL PRODUCTS FORMED IN SITU ON THE FLOOR OF THE OCEAN. 
The organic remains met with in marine deposits, as well as the' mineral particles 
derived directly from the crust of the earth and from extra-terrestrial sources, have been 
fully described in the preceding chapters. We have now to direct attention to some 
other substances in marine deposits, in the formation of which neither physiological nor 
physical phenomena can be said to be dmectly concerned. In the production of the 
substances to which w^e shall have to refer in this chapter chemical action plays the 
principal role ; these substances indeed owe their origin to the reactions between sea- 
water and the heterogeneous solid materials making up the bulk of marine deposits. On 
account of the great variety in the composition of the deposits, and the varied conditions 
under which the chemical changes take place, it is evident that the reactions resulting 
iu the formation of these secondary substances are of a very complex nature. What 
we here call chemical deposits are produced in situations rendering direct observation 
impossible, and under conditions differiug widely from those obtaining where somewhat 
similar products have been formed on terrestrial surfaces. 
It has been recently stated that the chemical action of sea-water is less powerful than 
that of pure water in bringing about the solution and destruction of silicates and other 
minerals.^ However this may be, it is known as a matter of fact that mineral substances 
are attacked by sea- water, and in the discussion of this subject it is important to remem- 
ber the influence time may exercise in all changes at the bottom of the sea, as well as 
the immense quantity of the solvent. The chemical products under consideration nearly 
all originate in a sort of broth or ooze, in which the sea-water is but slowly renewed. 
Many of them appear to be formed at the surface of the deposit, — at the line separating 
the ooze from the superincumbent water, where oxidation takes place. In the deeper 
layers of the deposit a reduction of the higher oxides frequently occurs, and at the 
surface of the mud or ooze there are many living animals as well as the dead remains of 
surface plants and animals. It must be admitted that the reactions referred to are 
effected very slowly, although there is evidence that in special localities, and at certain 
periods, some of them may be much accelerated. 
It is not proposed to enter into any general considerations wdth reference to 
such chemical reactions in sea- water, but in each particular case we will give 
1 Thoulet, “Solubilite de divers mineraux dans les eaux de la mer,” Comptes Bendus, tom. cviii. p. 753, 1889. 
(deep-sea deposits CHiLL. EXP. — 1891.) 43 
