=Wadi Yoider=, the next wadi to the east, is of considerable importance, as it drains the west portion of Gebel Elba and its heads are extremely rich in trees and other vegetation, while one of its tributaries contains a large well of good water (Bir Akwamtra). The main head of Wadi Yoider may be considered to be the wadi which bears the special name of =Wadi O Sir Hadal=, draining the south-west flanks of Gebel Elba and the north-west flanks of Gebel Hanquf, and heading in an easy pass close to the well of =Bir Salalat O Sir=, about 450 metres above sea-level. Wadi O Sir Hadal courses north-west between the mountain ranges for about eight kilometres, receiving a rather large feeder from the south about six kilometres below its head. It then emerges from the mountains and turns north among lower hills, here receiving the =Wadi Qeirat=, draining westwards from near the summit of Elba. A few kilometres further on it enters an open plain sloping rapidly downwards to the north, receiving the small and narrow =Wadi Siamtit= from between two high hill masses to the west. From here onwards Wadi Yoider courses in gentle curves a little north of east to reach the coast in about latitude 22° 27′. A well called =Bir Nabit=, situated in Wadi Yoider, a few hundred metres up from its mouth, is believed to yield only brackish water. In its journey to the coast Wadi Yoider receives several feeders from among the rugged granite hills of El Sela to the west of it, as well as the important =Wadi Akwamtra= from the north-east flank of Gebel Elba. The head of this Wadi Akwamtra is quite close to the summit of Elba, and its course is at first almost due west, afterwards changing to nearly north among the lower flanking hills, and dividing into two channels which re-unite lower down. =Bir Akwamtra=, one of the best water sources in the Bisharin country, is situated at an altitude of 330 metres above sea-level in the eastern channel of Wadi Akwamtra, about three kilometres up above the place where it leaves the hills. It is an excavation in the stony floor of the wadi. The water in April 1908 was about four metres below the wadi floor, and formed a pool about two metres in diameter in a wide open hollow which filled as fast as it could be emptied. The water was of excellent quality. There are two other wells a few hundred metres further down the same wadi; one of these contained a little water, while the other was dry, and only the principal well was being used. The floor of the wadi near and above the well is very stony, so that it is not a very good camping ground, and the Hamedorab Arabs pitch their tents of matting further down the wadi. When I visited the place there were numerous Bisharin Arabs at the well with their women and children, all busily employed in watering their flocks and herds and washing their clothes. The wadi, in spite of its stony floor, is literally full of large trees, principally acacias, so close together that laden camels cannot