onsisting chiefly of oxides of iron and manganese with salts of
magnesia and lime. It is supposed to be due to a chemical change
within the rock and not to deposition on the surface.]

_Minerals._--Egypt possesses considerable mineral wealth. In ancient
times gold and precious stones were mined in the Red Sea hills. During
the Moslem period mining was abandoned, and it was not until the
beginning of the 20th century that renewed efforts were made to
develop the mining industry. The salt obtained from Lake Mareotis at
Meks, a western suburb of Alexandria, supplies the salt needed for the
country, except a small quantity used for curing fish at Lake Menzala;
while the lakes in the Wadi Natron, 45 m. N.W. of the pyramids of
Giza, furnish carbonate of soda in large quantities. Alum is found in
the western oases. Nitrates and phosphates are also found in various
parts of the desert and are used as manures. The turquoise mines of
Sinai, in the Wadi Maghara, are worked regularly by the Arabs of the
peninsula, who sell the stones in Suez; while there are emerald mines
at Jebel Zubara, south of Kosseir. Petroleum occurs at Jebel Zeit, on
the west shore of the Gulf of Suez. Considerable veins of haematite of
good quality occur both in the Red Sea hills and in Sinai. At Jebel
ed-Dukhan are porphyry quarries, extensively worked under the Romans,
and at Jebel el-Fatira are granite quarries. At El-Hammamat, on the
old way from Coptos to Philoteras Portus, are the breccia verde
quarries, worked from very early times, and having interesting
hieroglyphic inscriptions. At the various mines, and on the routes to
them and to the Red Sea, are some small temples and stations, ranging
from the Pharaonic to the Roman period. The quarries of Syene (Assuan)
are famous for extremely hard and durable red granite (syenite), and
have been worked since the days of the earliest Pharaohs. Large
quantities of this syenite were used in building the Assuan dam
(1898-1902). The cliffs bordering the Nile are largely quarried for
limestone and sandstone.

Gold-mining recommenced in 1905 at Um Rus, a short distance inland
from the Red Sea and some 50 m. S. of Kosseir, where milling
operations were started in March of that year. Another mine opened in
1905 was that of Um Garaiat, E.N.E. of Korosko, and 65 m. distant from
the Nile.

_Climate._--Part of Upper Egypt is within the tropics, b