xc 
MANGANESE DEPOSITS OF ENDlA. 
previously put forward, the following ideas as to the origin of the 
deep-sea manganese nodules are formed : — 
1. The manganese, although probably partly derived from cosmic 
dust and volcanic debris, has been mostly precipitated 
from solution in sea-water, the manganese salts having 
been originally brought into the sea by rivers. 
2. The manganese oxide, although possibly partly precipitated as 
a result of the \ntal processes of organism?, both vegetable 
and animal, ha«! been mainly precipitated by calcium 
carbonate aided by the process of segregation from solution 
round a nucleus. 
3. Where the sea bottom consists largely of calcareous sediments, 
the precipitation may have been brought about mainly by 
the solution of some of this calcium carbonate, with the 
ft 
deposition of an equivalent amount of manganese oxide, 
owing to the presence of free oxygen 
4. Where the sea-bottom consists of red clay, it does so because 
the depths are there so great that the tests of thin-shelled 
organisms are completely dissolved by the sea-water before 
they reach the bottom. The calcareous matter in being 
dissolved deposits an equivalent amount of manganese 
oxide, which descends to the bottom, and there acts as a 
nucleus for the segregative extraction of manganese from 
the waters at the sea-bottom. The deposition of mangan- 
ese oxide by means of calcium carbonate associated with 
the red clays probably also occurs to a subordinate extent, 
for the shells of thick-shelled organisms may reach the 
bottom before being entirely dissolved. 
