a - 
cliv 
and the more western one via Boghari and Djelfa to Laghouat. 
The traveller from the green north of Europe, when passing 
through the gate of the desert at El Kantara, enters into a 
country almost contrasting as much with his own home as 
land with water, a new and strange world. At El] Kantara 
the first oasis of Date-palms greets him, and his eyes roam 
over bare hills which appear to him as a symbol of death; 
he is now in the Sahara, a broad desert belt stretching from 
the Atlantic Ocean eastwards and continued across Asia to 
near the shores of the Pacific. The damp north and north- 
west winds deposit in the Atlas Mountains the water they 
carry from the Ocean and Mediterranean, and the south-west 
winds become dry in Senegambia and the southern hills of 
the Sahara and sweep north without bringing relief to the 
thirst of the desert lands. When desiccation has once set in 
and the population does not or cannot counteract the dis- 
astrous effect the drought has on the vegetation, the process 
rapidly increases in intensity and sand replaces vegetation 
and conquers the country, just as in damp climates forest 
vegetation will cover the ground if unchecked. In Central 
Asia, at Buchara, the gradual destruction of the country by 
the sand has been going on in our time, settlements now 
being buried which were flourishing a few generations ago. 
There is little rain in the Sahara and what there is cannot be 
depended on, and when a storm breaks over the desert the 
water rushes away down the gullies of the hills or sinks deep 
into the sand. There is a system of rivers in the Sahara, but 
only the rivers which descend from the Atlas and are torrents 
when the snow melts, have running surface water all the 
year round, at least in their higher reaches. -The oases are 
in the river beds or near them, and their irrigation together 
with the dry air and the permeable soil are the cause of the 
rapid disappearance of the water from the surface. The water 
continues to run below the surface on an impermeable bed, 
and in many cases is cut off from the surface by a layer of 
gypsum, which must be broken through in order to reach 
the water. Here and there a pool is met within a river bed, 
and an exceptionally rich vegetation in a depression is always 
a sign of water not far from the surface, None of the rivers 
