410 T. W. E. DAVID. 
sheets of water derived from this source drain towards the south, 
and give rise to numerous springs along the whole length of the 
northern edge of the low lying Sahara. 
The waters from the Cretaceous springs disappear in the alluvial 
deposits of the Pliocene Formation and form small underground 
rivers, which flow towards the south and become united at a depth 
to form a main stream draining towards the south-south-east, 
under the lacustrine basin of the Pliocene Formation. The Oretace- 
ous beds being continuous under the Pliocene basin and dipping 
towards the Sahara, some of the springs derived from their porous 
strata break out considerably below the surface, and these of 
course assist the superficial springs in supplying water to the 
permeable beds of the Pliocene. The underground streams of the 
Pliocene basin flow in a number of reticulated underground 
channels like meshes of a net. These have been distinctly traced 
by means of bores for a length of one hundred and twenty kilo- 
meters (about seventy-four and a half miles) and a width of from 
four to eight kilometers. 
That the water circulates in distinct channels has been proved 
not only by the distribution of the successful bores, but also by 
the fact that small fish possessing perfect eyes, river crabs, and 
freshwater mollusca are brought up in considerable quantities at 
some of the bores. These have been caught in netting placed for 
the purpose over the discharge pipes at the bores. 
The presence of artesian water in the Pliocene strata of the 
Sahara has manifested itself in the form of “ behour,” natural 
Springs corresponding to the mound springs or mud springs of 
Australia. There is a tradition that artesian wells were first 
sunk in the Oued Rir District of the Sahara by the Arabs as far 
back as 1341. These native wells seldom exceeded two hundred 
feet in depth, many being not more than one hundred feet deep. 
They were timbered with logs cut from the date palm, and owing 
to the decay of the timber the native wells usually fall in and 
become completely choked up in from twelve to twenty years. 
