372 THE EMPTY QUARTER

BaniHubai - - White granite poor in biotite,

aplite.

Mahmal, between Bard White biotite-granite.
Eubai and 'Arq.

Country east of Tathlith ? Epidiorite.

West of Tathlith - - Microdiorite, red granite.

KhushaimDhib - - Red pegmatite, pink aplite, white

biotite-granite.

Al Muta'arridhat - - Altered basalt (? spilite), white horn-
blende-granite, epidote in vein-
quartz.

Dahthami - - - Red biotite-granite, altered dolerite.

Near Wadi Ranya - Banded rhyolite.

Raudhat ibn Ghannam - Red j asperized rhyolite.

Bir ibn Ghannam - Pink aplite.

Plateau of Sha'ib al Hornblende-biotite-granite, epidote in
Dha'a. vein-quartz.

Wadi Kara - - - Quartz-schist, and fine-grained gneiss.

Turaba - - - Hornblende-schist, quartz-porphyry.

There is no evidence of the age of the older volcanic rocks in this
part of the country or of the period of intrusion of the granites,
but they are in a general way similar to the old volcanic igneous
and metamorphic rocks from the Eastern Desert of Egypt on the
other side of the Red Sea.

At present no rocks intermediate in age between these old
igneous rocks and the fossiliferous Jurassic limestones of the
Tuwaiq plateau have been discovered. The Cretaceous rocks
are, like the Jurassic, pale cream-coloured limestones, but friable
sandy beds occur in the same region and form the lowest beds
exposed in the Buwaib pass. At Sulaiyil and Khashm Amur in
Wadi Dawasir compact yellow limestones overlie yellow sand-
stones. They contain fragments of shells but none identifiable,
A crystalline buff-coloured limestone was also found at Al Qaha.

Other compact cream-coloured limestones—but without
fossils—were collected at Dakaka Barbak and Raudha Barbak
(Summan), and between Al Jida and Shaukiya ridge (Hasa), also
south of Eufuf, on the ridge between TCVnn and Jabrin, and at
Qaliba and Maqainama, and at Wadi Dawasir. There is at
present no evidence as to the age of these rocks.

At Umm al Nussi and Hafair, south of Jabrin, broken nodules
of grey chalcedony were found, and drab-colouied flints were
scattered about at Haf air and Dharbun. Both flints and chalce-
dony were probably derived from limestone beds.