276 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1911. 
life throughout the world in every age since the Cambrian, and very 
certainly in pre-Cambrian times also, is sufficient indication that 
climatal conditions can not have been so extreme as to seriously 
inhibit denudation. It would be easy to cite evidence from sun- 
cracked sediments dating back to Torridonian times from teeming 
oceanic life now confined to tepid seas, but at various periods of 
geological history inhabiting every part of the ocean, and finally 
from forest growth and insect life on the land, that there is no evi- 
dence for continued lessened solar heat in past ages. 
But existing soil conditions might be exceptional. There are 
to-day great sheets of glacial clays spread over the northern lands of 
the earth. May they not affect the river discharge of sodium? 
The answer is to be found in the river analyses. It is sufficient to 
refer to the figures cited by Clarke in his Data of Geochemistry. 
There is no indication of excessive supplies from northern rivers. 
I am not aware of any sources of error other than those now con- 
sidered. It would appear that solvent denudation estimated in the 
only manner open to us assigns an age to the ocean which at its 
probable maximum does not exceed 100 million years. Assuming 
that certain sources of error combined to lower this age, for instance, 
that more complete knowledge will reveal a lesser sodium supply 
than has been determined on existing data; that the cyclic sodium 
should be taken as somewhat more than we have assumed; that 
former fluctuations of land area on the whole produced an effect on 
solvent denudation; assuming all this, we might be somewhat out in 
our reckoning. We have, however, neglected all those sources of 
error tending to increase the age unduly. Chief among these are 
the following: Primitive sodium existing in the ocean; marine solvent 
denudation effected directly on the coasts and sediments; sodium 
supplied with volcanic ejectamenta; sodium supplied by submarine 
rivers and springs. For a discussion of these sources of error I must 
refer to the several papers cited above. It is generally conceded 
that any precise evaluation of their effects is not possible; so that a 
considerable margin must be left when considering the minor limit 
of the age of the ocean by this method. ‘They certainly produce 
some effect as a set off to the corrections already dealt with. When 
all is considered, I believe it will be found that the most probable 
result based on solvent denudation is 100 million years, or close to 
this, and rather under this than over. It is against probability to 
add 50 per cent to this value. We can only double it by appealing 
purely and simply to the imagination for effects of which we possess 
no indication, and the existence of which is at variance with what we 
know. 
The age as determined is based upon the summation of the sodium 
supplied by the rivers during geological time. This mtegral can, 
