548 THE FRESH-WATER LOCHS OF SCOTLAND 
usually attributed to the light-emitting powers of minute organisms. 
On the other hand, it is stated ^ that the investigations of Ehrenberg 
and Lortet show the existence of " certain inferior organisms and 
microbes in the Dead Sea. 
NoRTHEEN The inland drainage area of Northern Africa (Sahara and Sudan) 
Africa. cQyej^-g ^n area of about 3,450,000 square miles (see fig. 65). 
The Sahara, the largest continuous desert on the earth's surface, 
stretches across the continent of Africa eastwards from the Atlantic 
for a considerable distance on both sides of the Tropic of Cancer, and 
forms part of the great arid belt extending across the Old World 
from north-eastern Asia to the borders of the Atlantic Ocean. To the 
north, in Morocco and Algeria, the limits of the region are defined 
by the Atlas range, but in other directions the boundaries are vague, 
and in the south the desert merges gradually and irregularly into 
the well-watered plains of the Sudan. The Sahara is a region of 
varied surface and irregular relief, ranging in altitude from 100 feet 
below sea-level to some 5000 or 6000 feet above it, and containing, 
besides sand-dunes and oases, rocky plateaus and ranges of hills. 
Sahara. The lakes of the Sahara are termed Shotts or Sebkas ; they are 
shallow, have no outlet, and are very salt, and in summer the heat of 
the sun often causes the water to evaporate, leaving behind a white 
sea of salt crystals. The streams flowing southward from the Atlas 
Mountains are diverted for irrigation purposes, so that the Shotts 
only receive their waters after the copious rains of winter and the 
melting of the snow in the mountains. Shott el Melrir, Shott el 
Gharsa, Shott el Jerid, and Shott el Fejej form a series of marshes 
or shallow lagoons extending from the south of Biskra (lat. 35° N., 
long. 5° E.) eastwards to the Gulf of Cabes, and occupy a depression 
below the level of the sea. At one time it was proposed by the French 
engineer. Colonel Roudaire, to Hood this region. Shott el Melrir 
occupies the bottom of the depression, and in summer its surface is 
partly covered with a coating of salt crystals, while its floor is covered 
by black, viscous mud emitting an odour of garlic, due possibly to the 
presence of volatile sulphur compounds ; veins of more solid ground 
form natural causeways. Shott el Jerid is the largest, and with its 
eastern extension, the Shott el Fejej, covei's an area of several hundred 
square miles. It lies about 60 feet below the sea, with which it seems 
formerly to have communicated through a now nearly dry coast stream. 
When on my way to Tuggurt in May 1900, I arrived on the 
cliff overlooking the Shott el Melrir late in the afternoon. The Shott 
was then a vast white expanse, which reminded me of the view of the 
Arctic Ocean from Flemish Cap at the north of Spitzbergen. Early 
1 Gautier, art.. "Dead Sea" m lincijd. Bihlica, vol. i. col. 1044, 1899. 
