ADEN PENINSULA. 6 



(a, c) of stiff clay or other impermeable material. These beds should 

 form a more or less complete basin or synclinal, and it is necessary that 

 some portion of the surface of the ground occupied by the bed c should 

 be at a lower level than the lowest point of the outcrop of h. Under 

 these circumstances, a certain proportion of the rain which falls on the 

 outcrop of h, and of the water which flows across it from and beyond a, 

 will soak into the porous material and permeate down to the lowest level d. 

 The impermeable bed a prevents the water sinking lower, or keeps it up, 

 while the bed c keeps it down. If then a boring be sunk at e down to 

 the permeable bed, the hydrostatic pressure of the column d h will force 

 the water to rise in the borehole and overflow the surface of the ground. 

 The statical rise of the water will be equal to e f, f being the level 

 of the lowest point of the outcrop of b. The actual height to which the 

 water will rise will however be less than ef, as it is reduced by and depends 

 on the amount of friction of the water and leakage through fissures, 

 as it descends through the permeable stratum and up the borehole. 



The above may be taken as the typical conditions required for an 

 artesian well. Let us then see how far, if at all, the geological structure 

 of the country under review approximates to them. 



Firstly, with regard to Aden itself. The peninsula, which has an 



extreme length from west north-west to east 



GeologtiTaspect. south-east of 54 miles and breadth from north 



north-east to south south-west of about 3^, attains 



its highest point in Shumshum, 1,776 feet above the sea. It consists 



entirely of volcanic rock, and is joined to the main land on the north 



by a narrow neck of low-lying ground about 1,000 yards wide, which 



is almost sub-merged at spring tide. To the north stretches a sandy 



plain for over thirty miles, and thus the peninsula is a completely 



isolated mass of hills which must be treated per se with respect to 



water-supply. On the opposite side of the harbour is the similar but 



smaller volcanic mass of Little Aden. 



( ;i59 ) 



