Professor J. Joly — The Age of the Earth. 223 



Before finally dropping the subject of the primitive ocean I must 

 refer to a remark of Mr. Fisher's to the effect — if I understand it 

 aright — that any assumption involving an original ocean free from 

 alkalies also involves chemical proportions between the alumina 

 and the alkalies in the original rocks. " If this proportion did not 

 hold there would have been either alumina uncombined in the 

 crystalline rocks or alkalies over to combine with the acids in the 

 ocean, presumably the latter, seeing that alkali salts abound in it 

 at present. That this due proportion should have existed does not 

 seem probable." I really see no reason why we should look for or 

 except any such equivalence between alumina and alkali. Why 

 not an excess of alumina over alkali ? Why not, when a glance 

 at Mr. Clarke's average crust-composition shows that there is 

 a very large excess of alumina over what is required to make felspar 

 molecules out of the alkalies or, for that matter, molecules of most 

 of the important alumina-alkali-silicates ; and fresh- water lakes of 

 to-day exist among such rocks ? Would any special difficulty arise 

 if these lakes were now to be formed by condensation of steam ? 



Mr. Fisher's criticism on the legitimacy of accepting the river 

 supply of sodium to the ocean is directed to the origin of the 

 chloride of sodium of the rivers ; contending that Clarke's crust- 

 percentage of chlorine (001) is inadequate to account for the 

 chlorine involved. Hence, he suggests, we must look to Sterry 

 Hunt's " fossil sea-water " contained in sedimentary rocks. 



With regard to this point it will conduce to clearness if I first 

 refer to the deductive allowance of sodium chloride required by the 

 presence of this body in rain-water. 



In my calculations I had allowed 10 per cent, of the chloride 

 of sodium of rivers as supplied by rain, and on this account not 

 entering the calculations. This, I of course admit, may have been 

 an insufficient allowance. But in the present state of our knowledge 

 on the matter I do not think more or much more is justified. Inland 

 rains show an ever diminishing percentage of salts, and again much 

 of the rainfall richest in salts — that falling immediately on seaboards 

 — finds its way back to the ocean in rills and streams, taking but 

 little from the land. The great rivers of the world, which 

 make up the bulk of the estimate of the river supply to the ocean, 

 gather their constituents from inland areas remote from the coasts. 

 On this point our knowledge will doubtless grow with the years. 



It will, however, clear away misapprehension as to the stress to 

 be laid on this matter if I state that, admitting very wide error on 

 my part in making this allowance, the final possible error involved 

 is quite limited in amount. Suppose, in fact, we extend the 

 allowance to a point certainly not justifiable, and assume half the 

 total NaCl of rivers to be derived from rain-water. Then 

 it will be found that the estimate of Geological Time increases from 

 90 to 100 millions of years. If, then, 10 per cent, is too small 

 and 50 per cent, is too large an allowance, we fix our limits as 

 between 90 and 100 millions of years. If we were sure of this 

 we might be well satisfied ! 



