13 MALLET : ADEN AND VICINITY. 



In the former case, there can be no doubt that the new wells, 

 situated as they must be, in ground already thickly dotted over with old 

 ones, would derive their supply chiefly at the expense of the latter, and 

 that the total yield would not be largely increased. The whole drainage 

 area to supply them is very limited, less than two square miles, and 

 the average annual rain-fall very small also, and it seems that the limited 

 quantity of water which exists stored up in the rocks, is already econo- 

 mized nearly as far as it can be. 



The second expedient, to deepen the wells, would not result in any 

 useful augmentation of the supply, for it appears from information 

 kindly obtained for me by Captain Mander, that the wells if sunk deeper 

 than at present, become more brackish. The bottoms of them- are now 

 below sea level, and they have all of them a more or less brackish taste, 

 although it is very slight in the best. Even into them it would seem 

 that there is some infiltration from the sea, and apparently as they are 

 sunk deeper and the hydrostatic pressure from the sea becomes greater, 

 the amount of infiltration increases. Such being the case, a deepening 

 of the wells would no doubt increase the yield more or less, but the 

 quality of the water would be deteriorated. 



I think there can be no doubt that the wells derive their brackish 

 taste mainly from the sea, as is sufiiciently shown by the undrinkable 

 quality of the wells in the town, and the increasing purity of the water 

 as they recede from the shore, as well as by the increased brackishness 

 if they be sunk deeper. A certain contingent of saline matter may, 

 however, be furnished by the rocks themselves. Chloride of sodium 

 is a very common mineral in volcanic rocks, and its presence in 

 those of Aden is shown by an efflorescence of it which I observed 300 or 

 350 feet above sea level, on the hillside above Toowye. Careful analyses 

 of the waters of the sea and of the difi'erent wells, might furnish data 

 to determine the relative proportions in which the well water is affected 

 by the sea and by the rocks. 



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