504. TRANSACTIONS OF SECTION C, 
been correlated. Certain rocks between the Bardon rock and the Peldar porphy- 
roid seem to bear some relation to the Felsitic Agglomerate, 
Birchili Plantation.—Recent research in this exposure has shown the identity 
of the rock with that found at Bardon Hill. On the north side rocks belonging 
to the Felsitic Agglomerate Series have also been found. 
Peldar Tor.—Yhe porphyroid exposed in the Jarge quarries contains inclusions 
of other rocks, which have been generally considered as segregation masses. An 
undoubted dyke in the middle of Peldar Tor has been exposed. 
Ratchet Hill.—An exposure in this hill shows the presence of rocks on the 
Felsitic Agglomerate horizon. At the north-west end a porphyroid occurs which 
seems to be identical with the porphyroid at Cadman Wood. 
Swannymote and Trilobate.— Rock helonging to the Felsitic Agglomerate Series 
runs between these two places, it has been much altered, and has not hitherto 
been recognised as belonging to the Felsitic Agelomerate. 
FRIDAY, AUGUST 2. 
The following Papers and Report were read :— 
1. Some Desert Features! By H. T. Furrar, M.A., F.G.S. 
Contrast between the deserts on either side of the Nile. 
The Western Desert, sometimes known as the Libyan Desert, presents all the 
features which one would expect to find in a region of deficient rainfall. There 
are broad featureless plains with no very definite drainage systems; there are long 
lines of sand-dunes stretching for tens of miles across the country; there are 
centripetal basins, and there are monadknocks or inselbergen, and an almost entire 
absence of vegetation. 
The Lastern Desert, or the Etbai, on the other hand, displays an integrated 
drainage system ; sand-dunes are conspicuous by their absence; vegetation is not 
searce; and comparatively high mountains form a backbone to the country. These 
mountains are a true chain and form the water-parting between the Nile and the 
ted Sea. ‘I'his water-parting is very much nearer the east coast, and, as in South 
Africa, so here we-have the shorter and steeper eastward draining wadis beheading 
the longer westward drainages. The highest peaks usually consist of granite, 
which is sometimes foliated, and these high peaks, which rise majestically above 
the denuded schistose rocks, are not always on the actual watershed. Forms of 
rock and mountain sculptured by sandblast are not obvious, for the rain whick 
occasionally falls destroys these and produces typical water-graded slopes, 
The western desert surfaces consist of a thin veneer of waste, except where 
monadknocks or the escarpments of the oases display solid rock. This veneer of 
waste is protected, as in the Antarctic regions, by a layer of pebbles, which prevents 
the wind transporting the lighter material and prevents the rain-water from flow- 
ing in definite channels. 
The eastern, or Etbai, desert shows bare hillsides, and the steep cliffs which 
form the wadi-walls are quite free from débris. The wadis or dry watercourses 
are at present being aggraded, and it is only in the wadi-beds that one finds the 
alluvium. This alluvium of boulders and rock-débris is usually from 5 to 50 ft. 
in depth, and may be described as a torrential deposit. The only sorting of 
materials that is obvious in this region is that sorting due to water-action, where 
the volume of water and the slope of the ground are the determining factors. 
Sorting of fine material from the coarse is not as common as one would expect. 
A high wind (Beaufort scale, force 8) will only move pebbles and grit less than 
5 mm. in diameter, so that a succession of winds of unprecedented force would be 
necessary to produce ‘pebble beds.’ The pebbles of the gravels on the western 
plateau, near Wadi Natrum, are all rounded and water-worn, and form a heavy 
' By permission of the Director-General, Survey Department, Egypt. 
