Appendix IL: Phytogeography and Geology. 1085 
considerable size, known as Birket-el-Quriim. The lake, which has 
a length of 40 kilometres, and a maximum breadth under ten, 
covers at the present time an area of about 225 square kilometres. 
It is entirely bordered by desert, along a large part of the southern 
side the cultivated land approaches its shore, although even here a 
large area actually bordering the lake is waste salty land as yet 
unfit for cultivation. Lake Moeris, being used as a regulator of 
excessively high and low Nile floods’), was of the greatest importance 
in connection with the irrigation of the Nile Valley. 
The phenomenon of the extraordinary freshness of the water of 
the Birket-el-Qurin has been commented on by Professor Schwein- 
furth, who shows that the degree of concentration of salt in a lake 
whose volume has been continually reduced, and to which salt has 
constantly been added, should be many times greater than the actual 
existing amount. An analysis”) of the water at the west end of 
the lake showed that the total salts amounted to only 1,34°/,, 
of which 0,92°/, was sodium chloride. Professor Schweinfurth 
coucludes that the lake has a subterranean outlet, which alone would 
enable it to maintain its comparative freschness”*). 
With the exception of the lake and the cultivated area the 
depression is practically entire desert. The part of the. Libyan 
Desert dealt with here has, excluding the cultivated land and the 
lake, an area of some ten thousand square kilometres. Some portions 
have been exactly examined and mapped, others are still very imper- 
fectly known, especially on the south and south-west sides. 
The rocks forming the area within the above limits are almost 
entirely of sedimentary origin, the exception being a band of hard 
basalt intercalated at the very top of the series and exposed only 
on the extreme northermost limit of the depression. 
The unique character of the Faytm is alone sufficient to show 
that special causes have acted in its production*). Two main causes- 
stand out: 1. the presence of thick bands of comparatively soft 
arenaceous and argillaceous strata breaking up the usually continuous 
hard limestone of the Middle Hocene; 2. the effect of the Nile 
valley fault in lowering the whole of the western desert (north of 
1) Herodotus, Book II. — Strabo, Book XVII. — Diodorus Siculus, 
Book I, Chap. LI. 
*) A preliminary Investigation of the soil and water of the Fayim 
Province by Sucas. Cairo 1902. — Survey Departement. 
8) Schweinfurth: On the salt in the Wady Rayan, in Willeocks: Egyptian 
Irrigation Appendix II, p. 460—465. 
4) Blanckenhorn: Geologie Aegyptens, parts I—IV. JZischrft. Geol. 
Gesell. Berlin, 1901. — Flinders Petrie: Hawara, Biahmu and Arsinoe. — 
Keypt Explor. Fund Reports 1889. -— Schweinfurth: Reise in das Depressions- 
gebiet im Umkreise des Faytim. — Zeitschr. Ges. f. Erdkde, Berlin 1886. 
