Joty—An Estimate of the Geological Age of the Earth. 63 
from a depth of 4956 metres, west of the Society Islands, gave 1°83 per cent. 
Na,O, and 1°74 per cent. of K,O.* In Murray and Renard’s Report of the 
‘“‘ Challenger” results, it is suggested that some of this voleanic débris 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 Na,O, 2°34, K,O, 1:61 per cent.; basaltic pumice, Na,O, 2°81, and K,O, 
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 71;th 
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.t 
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 remainder, 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 with 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. 
We can only, from what we know, gather some idea of the order of magnitude 
of the correction for oceanic solvent-denudation. It appears 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 thisis probably a major limit.§ Taking into 
* Rosenbusch, oc. cvt., p. 420. + 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,” 1., p. 147. 
§ See the Summary of positive and negative errors contained in Appendix IT. and, more especially, set 
off 1 and 2 of the errors going to make the estimate a maximum against 1, among those tending to render 
it a minimum. 
TRANS. ROY. DUB. SOC., N.S. VOL. VII., PART III. L 
