Chap. XX.J 
DEEP-SEA DEPOSITS. 
399 
miles. If we can assume that tliis represents roughly the average volume 
of the oceans during the whole of this period of ten milUon years, and that 
the average annual amount of river-water flowing into the sea during 
the same time is 6,-500 cubic miles, we see that the whole of the water 
. , ,-11 1. V 1 I, xi- • • 324,000.000 
of the ocean could have been supphed by the rivers in — — = 
.30,000 years approximately. 
The supply of river-water is of course kept up by the evaporation of 
sea-water and its precipitation on the land in the form of rain. In 
this process the dissolved salts are of course left behind in the sea ; hence, 
as in 10,000,000 years the rivers must have contributed the amount of 
water in the oceans ^'50 *^ ^0^ =200 times over, sea- water should contain 
200 times as much manganese per unit volume of water as average river- 
water. This means that a cubic mile of sea-water should contain man- 
ganese equivalent to 5,70.3 X 200 = 1,14:0,600 tons of manganese 
sesquioxide, supposing that all the manganese that has entered the sea 
during this 10,000,000 years has remained in solution in the sea-water. 
Now the figures given by Murray ^ for the dissolved matter in sea- water 
in terms of tons per cubic mile are as follows : — ■ 
Tons per cubic mile. 
Magnesium carbonate (MgCOs) 438,000 
Calcium carbonate (CiCO;?) 6,147,000 
Potassium sulphate (K2SO4) 
Sod'fjm chloride (NaCl) 
Magnesium chloride (MgCk) 
Magnesium sulphate (MgS04) 
Magnesium bromide (MgBro) 
3,723,000 
117,441,000 
10,419,000 
fi,.529,000 
328,000 
Total . 151,025,000 
From these figures of Murray it will be seen that haa all the man- 
ganese remained in solution in sea-water it would have formed 0*7% of the 
total salts and hence have been quite an important constituent^. 
It is of course known to be present in sea-water in small amounts ; thus, 
according to Forchhammer, as summarized by Dittmar^, manganese is 
readily detected in the residue left on re-dissolving sea-water solids in 
water. But the quantity is apparently so small that, as far as I know, 
1 Op. cit., Ill, p. 77. 
2 Had we considered a period of only 1,000,000 years, the value of the Mn203, 
114,060 tons per cubic mile, would still be too small to neglect, namely 0"07°/o of the 
total sea salts. 
3 Challenger Reports, Physics and Chemistry, Vol I, p. 2, (1884). 
