The canal leaves the Nile Valley at Lahûn (Plate II), and follows a somewhat serpentine course through the desert for about 5 kilometres, irrigating a narrow strip of land on either side, which at Hawara rapidly broadens out into the wide cultivated area of the Fayûm. Once within the latter, the Bahr Yusef gives off numerous subsidiary canals which traverse the country in all directions, constantly splitting up into smaller branches until the water-supply is divided throughout the whole area. With the exception of the self-contained basin of Gharaq, on the south side of the Fayûm, the entire district drains into the Birket el Qurûn, which occupies the lowest part of the depression, to the north of the cultivation. The basin of Gharaq is irrigated by the Bahr el Gharaq, a canal which takes off from the Bahr Yusef soon after the latter enters the Fayûm[6]. The cultivated land of the Fayûm is traversed by two main ravines, cut down in many places to the Eocene limestone below the alluvium (Plates III and V.) At the present time these ravines carry canals for irrigating the lower parts of the district, and also act largely as drains to the higher lands. They were probably initiated by the escape of water through breaches in the Bahr Yusef during flood time, and have since been deepened to their present dimensions. In addition to the main central cultivated area, the soil of which, as mentioned above, is essentially identical with that of the Nile Valley, large tracts of the surrounding country, more especially on the north, north-west, and west sides, are also covered with alluvial deposits. These latter, which include sands, sandy clays, and clays of a quite distinct type, represent the slowly formed accumulations of the quieter and more remote parts of the ancient Lake Moeris (and the earlier prehistoric lake). The material was mostly derived from the Eocene strata which formed the shores of the lake, augmented no doubt by a certain amount of very fine sediment drifted from the Bahr Yusef, and by sand blown in by wind. It is noticeable that the thickest and most sandy deposits occur near the borders of the lake site; when close under the Eocene cliffs, as along the north side above the Birket el Qurûn, the deposits closely resemble those of the latter. The finer more calcareous beds occur further out and the true marls were accumulated only at some distance from the shores of the lake. When in Ptolemaic times the lake became reduced to a fraction of its former size, large areas covered by these lacustrine clays were exposed and some portions were brought under cultivation. Subsequently, however, all these outlying districts were abandoned and became absorbed by the surrounding desert, until in modern times the cultivation was restricted to the central portion of the old lake bed, a portion almost identical with the area over which true “Nile Mud” had been deposited.