62 Joty—An Estimate of the Geological Age of the Earth. 
down in deep water. That the denudation here progressing is mainly mechanical 
is shown by the smooth surface of rock below water-line. Limestones bordering 
the sea are often deeply pitted by the solvent action of the weather above high- 
water mark; beneath this line all is polished smooth.* Of course this does not 
show that no solution occurs. It merely connects the retreat and undercutting of 
sea-coasts with the scouring action of hard silt in the water. 
A large part of the coastal lines of the Earth is, however, beach, where the 
wayes are in perpetual motion and where the rounding of the larger stones more 
especially testify to the activity of erosive action. But making no allowance for 
rock-bound coasts as a set-off against the neglect of the minor indentation of the 
shore line, and supposing the active motion of the waves to extend for a distance 
of 1000 feet into the shallow water, we have an area of 25,000 square miles over 
which the sea is in active motion. 
It is evident that even a very considerable rate of solution over this area would. 
bear but a small proportion to that progressing over the forty-four millions of 
square miles exposed to chemical actions for a large part, far more active than is 
exerted by sea-water, and generally in material finer in grain. 
This last point may be considered set at rest by the experiments of Daubrée. 
Enclosing three kilogrammes of felspar in fragments, along with water containing 
three per cent. of chloride of sodium, in the rotating cylinders used in his 
well-known experiments, and making all the conditions the same as those obtaining 
in his experiments in which fresh water was used, he could not obtain, either in 
a vessel of iron or of stone-ware, any alkaline reactions except the most feeble: 
‘‘ et incomparablement moindre que celle qui se manifeste dans l’eau distillée.” 
The presence of the chloride of sodium appeared to arrest the decomposition. 
To this inactive nature of sea-water the prolonged preservation of felspathic 
fragments on sea-beaches has been ascribed. 
There is interesting evidence bearing in this direction, to be derived from 
the deep-sea deposits. The volcanic débris, whether wind or water borne, must be 
in a fine state of comminution in order to reach the central oceanic deposits. 
Such particles must sink with extreme slowness through depths measured by miles. 
Their subsequent sojourn upon the bottom is of unknown duration. Yet it is 
remarkable that when these deposits are analysed the alkali ratio is that of the 
igneous, not that of the sedimentary rocks. This is a plain proof that the waters 
of the ocean do not affect them as would terrestrial rains and rivers. 
Thus we find a deep-sea ooze from 5422 metres deep between New Zealand and 
Tahiti to contain 4:92 per cent. of Na,O, and 2°82 per cent. K,O. Another, 
* In the neighbourhood of Dublin—at Donabate—this is clearly shown. 
+ ‘*Géologie Experimentale,” 1., p. 275. 
+ See Wallace’s “‘ Darwinism,” p. 363, for facts as to these dimensions. 
