610 PROF. J. W. GREGORY ON [Nov. I9II, 



The occurrence of boulders 3 feet in diameter embedded in an old 

 sheet of silt at the mouth of the Wadi Nagr, and of others lying on 

 the bed of the wadi west of the Wadi Susa, shows that the floods 

 have been of great power. Nevertheless, there does not seem to 

 me any adequate evidence of a greater rainfall in Cyrenaica in 

 historic times. 1 Northern Africa no doubt had a better rainfall than 

 at present, at the time of the glaciation of parts of North -Western 

 Europe : for the cyclonic systems, which now traverse Europe from 

 west to east, would then have followed a more southern path. But 

 that meteorological factor appears to have benefited Algeria and 

 the Atlas Mountains rather than Cyrenaica, for even the older 

 parts of the deep Cyrenaican wadis present the characteristics of 

 canons cut in an arid country. Nevertheless, it is probable that the 

 wadis were cut at a time of heavier rainfall than at present, for very 

 little excavation is now taking place in them. In some of the valleys, 

 such as the Wadi Khumas north of Slonta, various facts show that 

 there cannot have been any flow of water down the ravine for some 

 years past. Thus plants of several years' growth stand on the lowest 

 part of the channel ; traces of cultivation, which must have been 

 several seasons old, remain undisturbed on sheets of clay in depres- 

 sions of the river-bed ; footpaths have been worn clear of pebbles ; 

 and slight ridges of earth have gradually accumulated across the 

 dry river-bed. Just above the lowest part of W f adi Khumas the 

 valley contracts to a narrow gorge, which is filled with trees 

 and shrubs, and I could see no flood -marks upon them. There can 

 have been no heavy flood through this outlet for at least several 

 decades. Below this point, however, a large tributary comes in 

 from the north, from the neighbourhood of Messa ; and the traces 

 of recent movement of coarse gravel and the absence of shrubs from 

 the river-bed, show that water had flowed across that river-bed 

 within the last year or two. In the Wadi Jeraib some patches of 

 rolled shingle with only young vegetation give evidence of some flow 

 in a recent season ; but the amount cannot have been considerable, 

 for lower down the wadi the evidence of the flow had disappeared. 



There is no evidence of any considerable deepening of these wadis 

 in recent years. The largest cedars that we saw in Cyrenaica were 

 in the Wadi Jeraib, where they are growing almost level with the 

 river-bed, and chariot-tracks in the lowest part of the same wadi 

 show that the bed has not been appreciably lowered since Roman 

 times. Chariot-tracks worn in the limestone in other localities also 

 show that the wadis have not been materially deepened since the 

 Roman occupation. The gravel-platform at Bonmansur in the 

 Wadi Derna may have been partly worn away since its occupation 

 by Palaeolithic man ; but even there it is quite possible that no 

 appreciable change has taken place since his time. 



1 The conditions of existing rainfall and water-supply are stated in the 

 Expedition Report, pp. 5-6, 9-10, and in the Eeport by Mr. M. B. Duff, 

 pp. 38-44. The most reliable rainfall records available, those at Benghazi 

 from 1891 to 1894, are included in the table opposite p. 46. 



