FRESH WATER IN SAND BANKS. 467 



Among the most curious of the natural phenomena 

 presented by the sand banks which stretch from Ply 

 mouth round by Cape Cod, is that of the occurrence 

 of fresh water within a foot or two of the surface, 

 &quot; wherever there is a body of sand above the tide-level, 

 even with salt water on opposite sides, or altogether 

 surrounding it.&quot; Such facts have been long known to 

 navigators, and observed in various parts of the world ; 

 and this occurrence of fresh water is acknowledged to be 

 a most beneficent provision for the wants of the sea-faring 

 man. 



There are three ways of explaining this phenomenon. 

 Either the fresh water comes from springs which force, 

 their way up into the sand, or it is the salt water which, 

 by filtering through the sand, has become fresh ; or it is 

 the rain-water which has collected in the sand, and is 

 there held by the capillary attraction of the sandy par 

 ticles, floating by its lightness above the heavier salt 

 water beneath. The first cause is set aside by the facts, 

 that springs occasionally appear bubbling up below tide 

 level, without affecting such artificial wells, though dug in 

 their neighbourhood and that fresh water is in this way 

 to be found upon sand banks in a bay where it is very 

 scarce on the adjoining mainland. As to the second, it 

 is certainly a curious and interesting fact, that salt water, 

 by filtering through silieious sand, does actually become 

 less salt. Mr Cabot found that a solution of salt, by 

 passing through sand, lost two per cent of its specific 

 gravity ; and Berzelius and others long ago observed 

 that the first portions of water, holding common and 

 other salts in solution, which pass through a deep layer 

 of sand, are nearly free from salt, but that those which 

 follow come through with their original saltness. This 

 cause, therefore, does not fully meet the case. 



The third cause must, therefore, at present be most 

 relied upon. The porous sand absorbs nearly all the 



