370 REPORT— 1900. 



bined, on the basis that sensibly the whole o£ the chlorine now in the 

 ocean was then existent in the form of HCl. This amounts to a sub- 

 tractive correction of under 6 per cent, on geological time. After con- 

 sideration of all the facts, I do not think any further concession to the 

 popular assertion, that 'the sea was salt from the first,' can be made. 



A deduction is also suggested for direct solvent denudation by the sea. 

 The correction is taken as between 3 and 6 per cent., the basis of correc- 

 tion being the ratio of the tide- swept area to the total rainy land area, 

 and some experiments which appear to show that over the same area of 

 rock surface the rate of marine solution cannot be more than twenty times 

 the rate of atmospheric denudation These experiments are communicated 

 to this Section. They are somewhat incomplete, but their rough indica- 

 tion may be accepted as sufficient for the present purpose. 



Allowance is also made for the transport of sodium from the sea to the 

 rivers through the atmosphere. Data are required in order to define this 

 allowance more precisely. 



The brief review of the method before you also refers to the rock-salt 

 deposits. These appear to be quite negligible compared with the enormous 

 mass of chloride of sodium row in the ocean— suflicient to cover the entire 

 land area to a depth of 122 metres—unless deposits of this substance, far 

 greater than anything at present dreamt of, are discovered. 



Some other possible sources of error are considered, but these ■will more 

 fitly be referred to further on. 



It is a confirmation of the general validity of the method that accept- 

 ing — with slight modifications — -Mr. Mel lard Reade's estimate of the total 

 mass of detrital sediments, and a mean soda content of these sediments, 

 based on a very considerable number of analyses, we find that the resulting 

 total mass of contained sodium added to the soda equivalent of the sodium 

 now in the ocean suffices to restore to the adequate mass of parent 

 igneous rock a soda percentage approximately equal to that of the mean 

 igneous ci'ust-rock of the earth. In other words what sodium is con- 

 tained in the ocean is approximately equal to the amount which would 

 have been wasted from such a mean igneous rock upon its degradation 

 into the probable mass of detrital sediments. 



Finally we find the method affords on the basis of the best data 

 available a duration since subaerial denudation began of between ninety 

 and one hundred millions of years. 



Professor Sollas has really referred to the weakest point in this estimate 

 when lie questions the sufficiency of the data affording the annual river 

 supply of sodium. However, there is much reason to believe that the 

 nineteen rivers— a fair admixture of great and small ones — aflbrd an 

 approximation to the nature of what the world's rivers yield in the form 

 of dissolved matter to the ocean. The want emphasises Professor Sollas's 

 demand for more experiment, and Sir Archibald Geikie's for geological 

 co-operation. The data required are really of the easiest to obtain. 



The method is, of course, based on the principle of uniformity, but the 

 generalised nature of the measure of uniformity a,ct\i3l\y reqxaived is worthy 

 of attention. The claim is restricted to the association of atmospheric 

 loater and of rock over a surface of land approximately equal to the 

 present rainy area of the globe, the climatic conditions doubtless differing 

 in each geographical region from age to age, but on the whole preserving 

 an approximate uniformity in denudative effect, as measured, say, by the 

 solvent denudative work accomplished per million of years. 



