62 JoLY — An Estimate of the Geological Age of the Earth. 



down in deep water. Tliat the denudation here j^rogressing 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 tlie water. 



A large part of the coastal lines of the Earth is, however, beach, where the 

 waves 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 Daubr^e. 

 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 I'eau distillee." 

 The presence of the chloride of sodium appeared to arrest the decomposition. f 

 To this inactive nature of sea-water the prolonged preservation of felspathic 

 fragments on sea-beaches has been ascribed. 



Thei'e is interesting evidence bearing in this direction, to be derived from 

 the deep-sea deposits. The volcanic debris, whether wind or water borne, must be 

 in a fine state of comminution in order to reach the central oceanic deposits. J 

 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 NaoO, and 2*82 per cent. K2O. Another, 



* In the neighbourhood of Dublin — at Donabate — this is clearly shown. 



f "Geologic Experimentale," 1., p. 275. 



I See Wallace's "Darwinism," p. 363, for facts as to these dimensions. 



