JoLY — All Estimate of the Geological Age of the Earth. 63 



from a depth of 4956 metres, west of tlie Society Islands, gave 1-83 per cent. 

 NaaO, and 1-74 per cent, of K2O.* In Murray and Renard's Report of the 

 "Challenger" results, it is suggested that some of this volcanic debris may come 

 from submarine sources. In any case the pumice and glass of the ocean floor, 

 even when decomposed, retains its igneous alkali ratio. Thus andesitic pumice 

 contained NajO, 2'34, KoO, 1"61 per cent. ; basaltic pumice, NaoO, 2-81, and KoO, 

 1"24 per cent. Other concordant examples are given. 



Are we to make a correction for oceanic denudation ? Are the solvent effects 

 of a magnitude which would result in a noticeable fraction of our estimate of 

 geological time being in excess ? If we supposed that the solvent effect of the 

 waves acting on the full coast line of the Earth were not less, not even equal, but 

 10 times as great as what is continuously progressing in an equal area of the 

 soils, the disproportionality of areas reduces its present solvent effects to ylrth 

 of the effectiveness of the land in supplying soluble materials to the sea. This 

 would then be a correction of half a million of years on the time estimate.f 



In the coastal effects of to-day, this correction would be almost certainly 

 excessive. To these effects must be added those progressing on the immense 

 quantities of fine silt which the rivers pour annually into the oceans, and which has 

 been estimated by Sir J. Murray as 2 '5 cubic miles of sediment. Much of this 

 rapidly finds a quiet resting-place, and probably nearly perfect preservation near 

 the coasts. The remamder, borne into deeper water, must yield something to the 

 ocean. We have, as we have seen, evidence that this may not be much ; possibly 

 the half million years would more than cover the entire solvent effects of the ocean. 



We have to consider, indeed, in this matter that the ocean was not always 

 charged witli its present dissolved salts. The primeval ocean, most probably after 

 the free acids were satisfied in the solution of the silicates, carried chiefly chlorides 

 indeed, but chlorides of lime, magnesia and other metals. The subsequent changes 

 were those of replacement for the greater part. We have no reason, however, to 

 suppose that these salts could act substantially differently from the chlorides of 

 sodium now constituting the larger part of the chlorides. J 



We can only, from what we know, gather some idea of the order of magnitude 

 of the correction for oceanic solvent-denudation. It ajDpears almost certain that 

 this cannot exceed a very few million years. 



The allowances we felt justified in making in the earlier part of this paper left 

 our estimate at eighty -nine millions of years. The least speculative part of our 

 knowledge inclines us to believe that this is probably a major limit. § Taking into 



* Kosenbusch, loc. cit., p. 420. f See also "Island Life," p. 225, foot note. 



\ A. Agassiz thinks the solvent power of the ocean during some of the earlier geological deposits was 

 far less than during later times. See " Three Cruises of the Blake," i., p. 147. 



8 See the Summary of positive and negative errors contained in Appendix II. and, more especially, set 

 ofi 1 and 2 of the errors going to make the estimate a maximum against 1, among those tending to render 

 it a minimum. 



TBANS. EOT. DUB. SOC, N.S. VOL. VII., PART III. L 



