1904-1905-] Recent Views regarding Coral Reefs. 171 



and the basic eruptive rocks the lime is being liberated now, 

 as it was also in the past, through the action upon these rocks 

 of surface-water charged with weak solutions of the humus 

 acids. These acids originate through the action of bacteria 

 upon decomposing vegetable matters. 



The average percentage of salts held in solution by the 

 nineteen representative rivers of the globe just referred to 

 includes also 34,361 tons of sulphate of lime per cubic mile 

 of the river -water. Comparing the sulphate with the 

 carbonate, — i.e., 34,361 to 326,710, — these stand about as 

 one to nine. That is to say, river-water holds about nine 

 times as much of the carbonate as it does of the sulphate. 

 It may be well to add further that the percentage of 

 magnesium to calcium in river - water stands about as one 

 to three. 



In striking contrast to the figures just given are those 

 which relate to the relative percentages of the same sub- 

 stances as those mentioned when we have sea-water of average 

 composition under consideration. There is practically no 

 carbonate of lime in a cubic mile of sea- water. On the other 

 hand, the percentage of the sulphate is enormously increased 

 in proportion. Each cubic mile of sea- water holds in solution 

 no less than 5,437,000 tons of the siilphate of lime, instead 

 of the 34,361 tons in the same quantity of river-water. In 

 the present case, therefore, the proportion stands thus : 34,361 

 to 5,437,000, which is as 1 to 158-22, or nearly as 160 

 to 1. The proportions of magnesium to calcium are also 

 reversed, being in sea- water as 3 '8 5 to 1, instead of the 1 to 

 3 as it is in river-water. I may perhaps be permitted to 

 remark regarding this that, in a paper read before the Eoyal 

 Physical Society in 1889 (see "The Paste of Limestones," 

 ' Geol. Mag.,' III., vol. vii. pp. 73-78), Sterry Hunt's state- 

 ment that " if a solution of carbonate of lime in carbonated 

 water be mixed with a solution of sulphate of magnesia in 

 water, double decomposition ensues, and carbonate of magnesia 

 and sulphate of lime are formed," affords us the clue to what 

 happens. The carbonate of lime, transported ceaselessly by 

 rivers from the rocks of the land, does not reach the waters 

 of the sea in that form, but is changed into the sulphate 

 at the confluence of the two waters. It is therefore from 



