550 THE FRESH- WATER LOCHS OF SCOTLAND 
Shott el Tigri is wholly in Morocco. Shott el Gharbi, or Western 
Shott, is on the Morocco frontier, and is followed by Shott el Shergai, 
or Eastern Shott, 140 miles long, at the foot of Mount Saida. Then 
come the Zahrez-Gharbi, the Zahrez Shergai, the Shott el Hodna, 
and, beyond Batna, towards the Tunis frontier, the Tarf and other 
lagoons of the Haracta depression. 
The waters of many of the rivers that flow towards the Sahara 
either disappear in the permeable strata, or are buried by the drifting 
sand, and flow along the underlying clayey stratum. Owing to local 
causes, such as the cropping up of a bed of rock across its course, 
the buried water may come to the surface and form an oasis with an 
ordinary well, or it may be caused to rise by boring, thus forming an 
oasis with an artesian well. The many artesian wells sunk by the 
French in this region have brought fertility where there was formerly 
unproductive waste. In one part of the Sahara, the Souf, the water 
circulates close to the surface of the soil, concealed by a bed of sul- 
phate of lime, and in planting date-groves the entire crust is removed, 
the palms being planted in the water-bearing sand below ; this is 
termed an excavated oasis. 
The Oued Igharghar is a long depression, having its origin in the 
land of the Tuaregs on the Ahaggar plateau, about the latitude of the 
Tropic of Cancer, and extending northwards over 750 miles to Shott 
el Merwan, the southern extension of Shott el Melrir. About 60 miles 
above Shott el Melrir it is joined by a similar depression, the Oued 
Miya, and after the junction is known as the Oued Rhir. Although 
in many parts almost effaced by drifting sands, its bed is still followed 
by the native caravans. Salt lakes are found at intervals throughout 
the whole extent of the Oued Rhir ; and as the so-called Bahr Tahtani 
or ''Lower River,"" which flows along an impermeable bed beneath the 
channel of the Oued, has been reached by boring, a never-failing 
supply of fresh water can be obtained through artesian wells. The 
towns of El Marier, Tamena, Tuggurt, etc., are situated on a con- 
tinuous line of oases, many of which are artificially formed. The 
sinking of wells in this Oued led to the discovery of fishes, crabs, and 
fresh-water molluscs at considerable depths in the artesian well called 
Mezer, near Shott el Melrir.^ The presence of these fishes and crabs 
seems to prove the existence of running water beneath. 
In the zone of the Areg, or country of the sandhills, the moving 
sand arrests the course of the running water, and causes pools or 
marshes (Dhaya) to form, neither very large nor very deep. They are 
1 Ghromis Besfontainei, Chromii< Zilii, Hemichromis Saharce, HemichromiH 
Eollcmdi, Gyjjrifwdofi calarita7ms, Telphusa fluviatilis (see Paul Regnard, La Vie 
dans les Eaux, pp. ] 03-105, Paris, 1891) ; see also Tclnliatchef, "The Deserts of 
Africa and Asia," Eej?. Brit. Assoc., 1882, p. 356. 
