ft . 12.— 1860-1.] PROCEEDINGS, 1861. 



xvii 



experiments carried on by him on behalf of one of the London water- 

 supply Companies, and has shewn that " water containing' considerable 

 quantities of saline matter in solution, may, by percolating through great 

 masses of porous strata during long periods, be gradually deprived of its 

 salts, to such an extent as probably to render even salt water fresh. " 

 The difficulty which I felt in applying Darwin's ingenious theory to 

 the small coral islands in which fresh water abounds, as well as to wells 

 sunk in the coral formation at the north of Ceylon, arose from the fact, 

 that in the latter, rain falls with such proverbial infrequency as to be 

 inadequate to furnish the supply of fresh water invariably present ; whilst 

 in the numerous little coral islands to the west, the area of each is so 

 minute, that their surface, even in the most rainy seasons, could not 

 intercept enough to replenish the wells. Mr. Witt's discovery came 

 opportunely to aid, and facts arc recorded in other portions of my book 

 (vol. 1, p. 20; vol. 2, p. 536) besides those which alone Dr. Buist appears 

 to have seen, that in my mind establish the fact that these wells are 

 supplied, not by the banking in of rain by the surrounding salt water, 

 but by the slow percolation of water from the sea through the masses 

 of porous coral. 



J. Emerson Tennent. 



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