CX PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 1909, 



can be no doubt that the sea exerts a powerful chemical action on 

 many of the rocks with which it is brought into contact. Joly 

 has himself made experiments, 1 with a view to obtaining light on 

 this question. On the coast of Howth, near Dublin, I have been 

 especially impressed by the complete decomposition suffered by the 

 numerous dykes of diabase which are exposed along the cliffs to the 

 disintegrating effects of sea-water. Many of them have entirely 

 lost their original character, and now consist of soft porous clay. 



Prof. Joly has attributed about 3 to 6 per cent, of the total supply 

 of sodium to marine action, an allowance which seems generous 

 when it is considered that the total area of the tide-swept region is 

 to that watered by the rain as 1 : 700 only. But, on the other hand, 

 the action of the sea is not confined to the selvage between tides, 

 it extends far deeper into the land : how far, it is at present 

 impossible to say. "We have already referred to the results of 

 boring on Molokai, where sea-water was encountered at depths of 

 from 120 to 160 feet at several points along the coast. How far 

 inland these wells were situated is not stated, but their sites are in 

 several cases as much as 50 feet above sea- level. 



Observations made on Funafuti showed that the upper portion 

 of this island is freely accessible to the sea. The rise and fall of the 

 tide is accompanied by a subterranean inflow and outflow of sea- 

 water, and a corresponding submersion and emersion of the ground, 

 which occurs in the very middle of several of the islets. This 

 moving water acts as a powerful solvent on the limestone-rocks. 

 In a bore-hole put down on the seaward margin of the storm-beach 

 the ebb and flow of the tide produced its full effect down to a depth 

 of 46 feet. 



A certain amount of sodium-bearing material is contributed 

 directly to the sea by volcanos. Vast masses of floating pumice 

 are sometimes met with far from land, and volcanic ash is widely 

 distributed by the winds, The red clay of the Ocean so widely 

 disseminated through abyssal deposits bears testimony to the dis- 

 integration which this experiences in the sea. 



The amount of sodium derived from this source is probably too 

 small to seriously affect our estimates, but volcanic activity as a 

 whole must play a very important part : we can observe its super- 

 ficial manifestations in the escape of acid gases and the emission of 

 juvenile waters, and at times denudation exposes some of its deeper- 



1 J. Joly, ' Experiences sur la Denudation par Dissolution dans l'Eau Douce 

 & dans l'Eau de Mer ' Compt. rendu Vllleme Oongres Geol. Internat. Paris 

 1900 (Paris 1901). 



