xxxvi INTRODUCTION. 
reached in three marches from the confines of Siwah. This salt lake was first made 
known to Europeans by Cailliaud, who was also the first to traverse the route which 
has since been explored by Pacho, Rohlfs, Zittel, Jordan, and other travellers, llohlfs 
says that the Sittrah lake is defined on the north by a picturesque rocky chain and on 
the west and east by reeds ; and Cailliaud mentions that on the south side, in his day, 
there was a great bank of sand with a few date-palms. When llohlfs visited Sittrah 
the surface of the lake was covered with ducks and white ibis. About half a mile from 
its southern end, where the route passes, there is a fresh-water spring at the foot of a 
date-palm, and some marshy land covered with reeds ; but here, as in Aradj, mosquitoes 
are so numerous that neither man nor beast can endure their attacks, and consequently 
a camping-ground has to be sought for further to the east, where there is a little herbage 
for camels. Cailliaud continued on to the oasis of Baharieh ; and Jordan, when he 
separated from Rohlfs at the Sittrah lake, in 1874, followed a route slightly to the north 
of that taken by the French traveller. 
As Eohlfs accompanied by Zittel proceeded to the oasis of Farafreh, a knowledge 
of this part of the Libyan desert is gained by their experiences. Along this route 
there are great collections of sand, not, however, in the form of continuous dunes, but 
as confused masses very difficult to cross, and giving rise to great fatigue. In 
proceeding from the Sittrah lake the route traverses an eastern rounded arm of the 
sand-sea, 47 metres above sea-level, and then passes over a short western prolongation 
of the plateau 104 metres high, to descend again to another arm of the sand-sea only 
10 metres above the Mediterranean, after which the plateau is once more reached, 
rising in a gentle slope to the south-east, until at the summit of the escarpment of 
Farafreh (Introd. PI. V.j it is elevated 242 metres above the Mediterranean. The 
distance between the Sittrah lake and Farafreh is accomplished in six marches ; only 
traces of vegetation occur here and there along this route. 
Cailliaud mentions that, after leaving the Sittrah lake, on his way to Baharieh, scant 
herbage was found, but after this, at the foot of a long mountain, there was a great 
extent of sand impregnated with salt, associated with which there was a small collection 
of saline water which his guide assured him had formerly constituted a part of the 
Sittrah iake. Beyond this point the desert rises to 47 metres, again falling to 
43 metres, and rising once more to 80 metres, followed by a descent to 08 metres, 
with a high desert escarpment on each side of it. This slight depression is the well- 
known Bahr-bela-ma., which is bordered by rocks about 20 metres high and partly by 
slopes and sand-dunes. Zittel states that this valley has nothing in common with 
a river but the name, and llohlfs says it is of so little importance that it may hence- 
forth disappear from the maps. It passes into the nummulitic plain to the east and at 
last into sand-dunes. As sand is less frequent on this route to Siwah than on that from 
the Fayum, Cailliaud supposed this was the reason why the ancients preferred it to the 
the latter. Jordan, when in the neighbourhood of the Bahr-bela-ma. (4th March) 
