— 114 — 
of re-made limestone, interbedded with frequent layers of conglomerate and 
gravel, washed down by the larger streams and by torrential floods. In the 
quieter parts of these lakes clays and calcareous tufas were laid down and are 
visible to-day from Kom Ombo to Heluan. Subsequently, owing to the breaking- 
down of the dividing barriers, or as the result of a general slight elevation, 
drainage became more pronounced and the river cut its way down through these 
lacustrine deposits. It was probably at this time that, following the partial 
removal of the gravel ridge between the Fayum and the valley, part of the 
drainage obtained access to the Fayum depression and a lake, the precursor of 
the historical Moeris, was formed. Subsequently, under climatic conditions 
similar to those of to-day, the accumulation of Nile alluvium commenced within 
the wide trough cut out in the older lake beds. Flood plains were formed on 
either side of the river, and by successive deposits, at the rate of about twelve 
centimetres a century, were built up to their present level. 
52. Economic products. Limestones for building and other purposes are 
abundant in the Lower and Middle Eocene formations, though as a rule of only 
medium quality. The chief quarries are those of Jebel Mokattam, Tura, Heluan, 
Abu Foda, Haridi, and el-Tarif. At Isawia, near Tahta, a fine tough freshwater 
tufaceous limestone of Pleistocene age occurs, and was largely used in the 
construction of the Assiut barrage. Clays of good quality are not widely 
extended, though certain bands of the Esna shales are very largely used near 
Qena in the manufacture of pottery. For bricks the Nile alluvium is used 
throughout the country. 
Sandstone is quarried for local purposes at J. Ahmar near Cairo and in several 
localities in the south part of the country ; it was formerly extensively quarried 
at J. Ahmar for the temples of the Delta, at J. Silsila for those of Upper Egypt, 
and at Girtassa, south of Assuan, for the Nubian monuments. Although a fairly 
hard and good weather-resisting stone when carefully selected, the frequent 
presence of soft uncemented and clayey laminae gives it an unreliable character, 
and a good deal of the decay of many of the ancient Egyptian monuments is 
attributable to this cause. 
Numerous rocks in the Hed Sea Hills and the Nile Valley were worked in 
Egyptian and Homan times for ornamental purposes ; among them may be 
specially mentioned the purple imperial porphyry of J. Dokhan, the green breccia 
of Wadis Hammamat and Dib, the doleriteof Wadi Esh, and the hornblende 
granite of the first cataract. In modern times local granite was used throughout 
the Assuan dam and an Oligocene basalt is quarried at Abu Zabel and used for 
road-metal in the capital and other towns. 
Old workings and mining camps are of common occurrence in many parts of the 
Eastern Desert and there is no doubt that considerable quantities of gold were 
extracted by convict labour. The quartz lodes traverse not only the metamorphic 
rocks but also some of the granites. Iron (hematite, limonite), copper (chryso- 
colla, copper pyrites) and lead (galena) bearing veins also occur, and turquoise, 
jasper and chrysolite are found in certain localities. Petroleum and sulphur occur 
sparsely near J. Zeit, and gypsum in large quantities in many parts of the 
country. 
