kN ESTIMATE OF THE GEOLOGICAL AGE OF THE EARTH. 285 

 IX. — THE SOLVENT DENUDATION OF THE OCEAN. 



This subject, of course, closely concerns the matter discussed in this 

 paper. To assume that no solvent action was exerted by sea water 

 upon the coasts and the detrital remains continually being poured into 

 it would, of course, be erroneous. We can only hope, in the present 

 state of our knowledge, to find some clue as to the magnitude of the 

 time allowance justified by marine solvent denudation. 



In the first place, it is to be noticed that this denudation nnistbo pro- 

 gressing chiefly along the immediate coast lines of the land areas. We 

 can readily arrive at a rough estimate of the area involved. Measure- 

 ment on a terrestrial globe shows that the coast lines of the continents 

 and principal islands amount to 132X10'' miles. ^ Much of this is rock 

 bound. Along the rock-bound shores the rate of denudation apart 

 from attrition is proba])ly extremely slow. Soils can not here accumu- 

 late. Particles removed by attrition are carried out and quickly laid 

 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 seacoasts 

 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 waves are in perpetual motion and where the rounding of 

 the larger stones more especiall}" testifies 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 

 1,000 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 

 Daubree. Inclosing 3 kilograms of feldspar in fragments along 

 with water containing 3 per cent of chloride of sodium in the rotating 

 cylinders used in his well-known experiments, and making all the con- 

 ditions 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 



^Croll, allowing for bays and inlets and the smaller islands, estimates the cost line 

 at 116X10'' miles. Wallace takes 100X10* miles. See Island Life, p. 221. 

 -In the neighborhood of Dublin — at Donabate — this is clearly shown. 



