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 deterrnined 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 riv»rs during geological time. This integral can, 



