c mill. It is the dissolved rocks of the Earth
which give it at once its brine, its strength, and its buoyancy.
The rivers which we say flow with "fresh" water to the sea
nevertheless contain those traces of salt which, collected over
the long ages, occasion the saltness of the ocean. Each gallon of
river water contributes to the final result; and this has been
going on since the beginning of our era. The mighty total of the
rivers is 6,500 cubic miles of water in the year!

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There is little doubt that the primeval ocean was in the
condition of a fresh-water lake. It can be shown that a primitive
and more rapid solution of the original crust of the Earth by the
slowly cooling ocean would have given rise to relatively small
salinity. The fact is, the quantity of salts in the ocean is
enormous. We are only now concerned with the sodium; but if we
could extract all the rock-salt (the chloride of sodium) from the
ocean we should have enough to cover the entire dry land of the
Earth to a depth of 400 feet. It is this gigantic quantity which
is going to enter into our estimate of the Earth's age. The
calculated mass of sodium contained in this rock-salt is 14,130
million million tonnes.

If now we can determine the rate at which the rivers supply
sodium to the ocean, we can determine the age.[1] As the result
of many thousands of river analyses, the total amount of sodium
annually discharged to the ocean

[1] _Trans. R.D.S._, 1899. A paper by Edmund Halley, the
astronomer, in the _Philosophical Transactions of the Royal
Society_ for 1715, contains a suggestion for finding the age of
the world by the following procedure. He proposes to make
observations on the saltness of the seas and ocean at intervals
of one or more centuries, and from the increment of saltness
arrive at their age. The measurements, as a matter of fact, are
impracticable. The salinity would only gain (if all remained in
solution) one millionth part in Too years; and, of course, the
continuous rejection of salts by the ocean would invalidate the
method. The last objection also invalidates the calculation by T.
Mellard Reade (_Proc. Liverpool Geol. Soc._, 1876) of a minor limit
to the age by the calcium sulphate in the ocean. Both papers were
quite unknown to me when working out my method. Halley's paper
was, I think, only brought to light in 1908.

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by all the rivers of the world is found to be probably not far
from 175 million tonnes.[1] Div