130 THE FUTURE OF ARID LANDS 
structure causes the holding up of water above and quite separate 
from the main table. The controlling factor is often a bed of 
shale or clay occurring as a lens or fold between the aquifers. 
Several examples of this type were developed in the Western 
Desert during World War II. 
Wartime experience in the eastern Egyptian Desert (Red Sea 
Hills), where rainfall is extremely small and sporadic, showed 
that by careful attention to geology, aided by geophysical meas- 
urements, underground reservoirs of drinkable waters could be 
found (23); of ten wells with drinkable water, five were of irriga- 
tion quality, but the yields were only a few hundred gallons an 
hour with a limited life, and therefore useless for irrigation 
schemes. 
As in a number of well-known cases in northern Africa, the 
geological structure of some deserts is such that deep boreholes 
in them tap artesian supplies of fresh water derived from humid 
regions far beyond the desert margins. 
In general, the overpumping of ground water supplies in arid 
lands, where it does not lead to exhaustion, gives rise to increasing 
salinity; rare exceptions to this are known, as where the abstracted 
saline water is replaced by a new acquisition of infiltrated rain 
water. Shaw (24) has shown that at Ma’an in Trans-Jordan, over 
a period of eight years, while the effect of pumping in certain 
wells was to increase salinity either at once or after a time lag, a 
complete recovery could take place even after considerable periods 
of heavy pumping have raised the salinity to very high figures. 
Apart from the development of rare surface and shallow ground 
water supplies, the indispensable tool in the investigation and 
development of the water supplies of arid lands is the water- 
boring machine, used with proper regard to the prevailing geologi- 
cal and hydrogeological factors. In the British Overseas and 
Commonwealth Territories, for example, large sums have been 
spent on these operations in recent years for the benefit of the 
local inhabitants and for ranching and other projects, and in 
every territory active teams are now busily engaged on extended 
programs of amelioration and development (5-8). As far as the 
local inhabitants are concerned, the beneficial use of the new 
