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The foregoing method of investigating the statistics of solvent denudation is capable of affording information not only as to the amount of sediments upon the land, but also as to the quantity which is spread over the floor of the ocean.

We see this when we follow the fate of the 33 per cent. of dissolved salts which has been leached from the parent igneous rock, and the mass of which we calculate from the ascertained mass of the latter, to be 27 x 1016 tonnes.  This quantity was at one time or another all in the ocean.  But, as we saw above, a certain part of it has been again abstracted from solution, chiefly by organic agencies.  Now the abstracted solids have not been altogether retained beneath the ocean.  Movements of the land during geological time have resulted in some portion being uplifted along with other sediments.  These substances constitute, mainly, the limestones.

We see, then, that the 27 x 1016 tonnes of substances leached from the parent igneous rocks have had a threefold destination.  One part is still in solution; a second part has been precipitated to the bottom of the ocean; a third part exists on the land in the form of calcareous rocks.

Observation on the land sediments shows that the calcareous rocks amount to about 5 per cent. of the whole.  From this we find that 3 x 1016 tonnes, approximately, of such rocks have been taken from the ocean.  This accounts for one of the three classes of material

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into which the original dissolved matter has been divided.  Another of the three quantities is easily estimated:  the amount of matter still in solution in the ocean.  The volume of the ocean is 1,414 million cubic kilometres and its mass is 145 x 1016 tonnes.  The dissolved salts in it constitute 3.4 per cent. of its mass; or, rather more than 5 x 1016 tonnes.  The limestones on the land and the salts in the sea water together make up about 8 x 1016 tonnes.  If we, now, deduct this from the total of 27 x 1016 tonnes, we find that about 19 x 1016 tonnes must exist as precipitated matter on the floor of the ocean.

The area of the ocean is 367 x 1012 square metres, so that if the precipitated sediment possesses an average specific gravity of 2.5, it would cover the entire floor to a uniform depth of 218 metres; that is 715 feet.  This assumes that there was uniform deposition of the abstracted matter over the floor of the ocean.  Of course, this assumption is not justifiable.  It is certain that the rate of deposition on the floor of the sea has varied enormously with various conditions—­principally with the depth.  Again, it must be remembered that this estimate takes no account of solid materials otherwise brought into the oceanic deposits; e.g., by wind-transported dust from the land or volcanic ejectamenta in the ocean depths.  It is not probable, however, that any considerable addition to the estimated mean depth of deposit from such sources would be allowable.