O MALLET : ADEN AND VICINITY. 



since their orig'inal formation. Sucli is particularly the case along the 

 ridg-e between Shumshum and the main pass) exactly the reverse of the 

 basin shaped form which beds should have, in which we seek water by 

 artesian wells. Thus the water stored up in any porous bed must, in 

 descending" along the dip, be scattered in diverging radial lines instead of 

 concentrated in converging ones, and any artesian boring sunk on the 

 outer flank of the crater could only tap the water flowing along one of 

 these lines. 



Next, with reference to the catchment area. Supposing the 

 porous lava bed between two compact ones to be found, -the whole 

 catchment area would be the outcrop a-o of such bed on the pie- 



Fig. 3. Ideal section shewing escarpments of beds. 



cipitous inner . wall of the crater, probably not exceeding at most 

 a few score yards in breadth, measured horizontally or in plan with 

 reference to rainfall. The plateau h-d (p. 4) which would furnish a greater 

 area, is, as far as I saw, composed chiefly of hard non-porous lavas, 

 and they probably form a great amorphous mass, the result of cooling 

 after the last eruptions of fluid lava in the crater itself, being therefore 

 unstratified and not underlying the beds which form the flanks of the 

 volcano. Further, as I have previously said, the flanks of the volcano 

 have suffered enormously from denudation, as may be well seen in 

 steaming along the southern shore. At the top, for several hundred 

 feet, are precipitous cliffs, and below them the mountain side is cut into 

 spurs and deep ravines. The denudation has apparently removed the 

 ( 264 ) 



