country and continues as a broad sandy valley, curving gently in a northerly direction, to latitude 23° 5′. Beyond this point, where it receives the Rod Mukrayib and the Wadi Kolaiqo from the west and east respectively, Wadi Madi becomes narrower, and winds about, though still keeping a general northerly direction, among low hill country to its junction with Wadi Hodein. Wadi Madi has many tributaries, the chief being the Wadis Shellal el Gharbi, Tugudbaia, Sinatib, Atluk and Kolaiqo, and the Rod Mukrayib, which will be treated separately further on. The upper parts of Wadi Madi and many of its tributaries are well stocked with trees, but its central parts, where it is wide and sandy, are more barren. Its principal head, the Wadi Eirahimib, falls at an average rate of sixteen metres per kilometre; from near Gebel Tueiwi to Bir Madi the average slope is nine metres per kilometre; while in the final fifty-four kilometres of its course from Bir Madi to Wadi Hodein, the average gradient is rather less than six metres per kilometre. =Wadi Shellal el Gharbi=, a tributary of Wadi Madi, originates in the mountains about six kilometres north of the highest peak of Gebel Gerf, where a pass connects it with Wadi Shellal el Sharqi, a tributary of the eastward draining Wadi Radad. Flowing at first nearly due west, Wadi Shellal el Gharbi receives the =Wadi Um Reddam=, which collects the drainage from the north faces of the highest peaks of Gebel Gerf. Two of the heads of Um Reddam lead to passes; one eastward to Wadi Shellal el Sharqi, and one westward into the head of Wadi Eirahimib. Entering a lower hill country from which it receives numerous feeders, Wadi Shellal el Gharbi turns north-west to join Wadi Madi about eight kilometres below Bir Madi. It has a rather rapid fall, and contains a fair quantity of trees and bushes. Its total length along its main channel is twenty-one kilometres. =Wadi Sinatib=, which enters Wadi Madi about six kilometres below Shellal el Gharbi, is a small wadi coursing north-west through the low hill country north of Wadi Shellal. =Wadi Tugudbaia= conveys to Wadi Madi the drainage from the dyke country south-east of Gebel Niqrub el Foqani. It is only a short wadi, and enters Wadi Madi nearly opposite Sinatib. =Wadi Berendiyeb=, which joins Wadi Madi from the west about latitude 22° 54′, drains the western flanks of Gebel Niqrub el Foqani. It is a many headed wadi, coursing at first among the low foot-hills of the mountain, and then crossing almost a sandy plain to join Wadi Madi. Its length along its main channel is about twelve kilometres. North of Berendiyeb, there are two other feeders of Wadi Madi coming from the low hills north-east of Gebel Niqrub el Foqani; they have no special names, being broad and sandy and without much vegetation in consequence of their draining only low country.