tless grains of which it is composed is
enormous. In a cubic foot of average soil the surface area of the
grains may be 50,000 square feet or more. Hence a soil only two
feet deep may expose 100,000 square feet for each square foot of
surface area.

It is true that soils formed in this manner by atmospheric and
organic actions take a very long time to grow. It must be
remembered, however, that the process is throughout attended by
the removal in solution: of chemically altered materials.

Considerations such as the foregoing must convince us that while
the accumulation of the detrital sediments around the continents
is largely the result of activities progressing on the steeper
slopes of the land, that is,

39

among the mountainous regions, the feeding of the salts to the
ocean arises from the slower work of meteorological and organic
agencies attacking the molecular constitution of the rocks;
processes which best proceed where the drainage is sluggish and
the quiescent conditions permit of the development of abundant
organic growth and decay.

Statistics of the solvent denudation of the continents support
this view. Within recent years a very large amount of work has
been expended on the chemical investigation of river waters of
America and of Europe. F. W. Clarke has, at the expense of much
labour, collected and compared these results. They are expressed
as so many tonnes removed in solution per square mile per annum.
For North America the result shows 79 tonnes so removed; for
Europe 100 tonnes. Now there is a notable difference between the
mean elevations of these two continents. North America has a mean
elevation of 700 metres over sea level, whereas the mean
elevation of Europe is but 300 metres. We see in these figures
that the more mountainous land supplies less dissolved matter to
the ocean than the land of lower elevation, as our study has led
us to expect.

We have now considered the source of the detrital sediments, as
well as of the dissolved matter which has given to the ocean, in
the course of geological time, its present gigantic load of
salts. It is true there are further solvent and chemical effects
exerted by the sea water

40

upon the sediments discharged into it; but we are justified in
concluding that, relatively to the similar actions taking place
in the soils, the solvent and chemical work of the ocean is
small. The fact is, the deposited detrital sediments around the
continents