274 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1911. 
may derive from the ancient salt deposits which have been impounded 
from the Sea is cyclic. 
The influence of wind-borne sodium has been fully diccuceed by 
Sollas, Clarke, and Becker. There can be no doubt that it is rela- 
tively unimportant. My own original correction was 10 per cent of 
the river supply. Becker, by examining typical cross sections of the 
isochlors, determined for the rainfall of western North America by 
the United States Geological Survey, finds that an allowance of 6 
per cent is sufficient. Sollas shows that these isochlors indicate that 
but a small fraction of the sodium chloride of the American rivers 
can be referred to this source. Clarke, by a somewhat different line 
of attack, concludes that a correction of 7 per cent on the sodium 
conveyed by the rivers of the United States is a maximum allowance. 
Clarke further considers that a correction for sodium chloride carried 
as dry dust is unnecessary. 
In a paper contributed by me to the Geological Magazine (May, 
1900) I considered the possibility of oceanic sodium existing dissemi- 
nated in the sedimentary rocks. Such sodium would be of course 
cyclic. It was easy to show that, even on excessive estimates of the 
occluded sodium chloride in such rocks, taken in conjunction with 
their rate of removal by denudation, this source of supply to therivers 
is less than 1 per cent. Clarke reconsiders the question and finds 
the allowance would not be more than 1 per cent. Three per cent is 
regarded by Clarke as a maximum deduction for sodium artificially 
supplied in modern times to the rivers. 
Oceanic salt deposits are not very abundant over the surface of 
the earth, being. generally confined to particular formations. That 
they seriously affect the river analyses of all the great rivers of the 
world is in the highest degree improbable. In any case if we deduct 
all the chlorinated sodium from the river supply we must include 
also all sea-derived sodium. If we effect this calculation, we obtain 
an age of about 150 million years. I do not think it will be disputed 
that this figure is in its nature excessive. 
There remains the possibility (d) that the assumed uniformity of 
past and present conditions is illusory; in other words, that special 
conditions now exist tending to bring about an abnormally great 
river supply of sodium. 
The present is admittedly a period of large land exposure. This, 
however, involves a fact which must be held in mind. At the pres- 
ent time the land area actually draining into the ocean is about 39.7 
millions of square miles. The total land area is, however, rather 
over 55 millions of square miles. It follows that about 30 per cent 
of the land area contributes nothing to the ocean. Or, again, the 
areas which are classed as “‘rainless’—that is, which have less than 
an annual rainfall of 10 inches and have no run-off—are estimated as 
