152 Scientific Intelligence. 



six feet across the top and is 390 feet high ; it is bounded by 

 nearly vertical walls of sandstone. The yellowish white sand 

 rests on the rocks at the high angle of 31°, is very fine grained, 

 and composed chiefly of quartz and calcareous sandstone. The 

 grains are well rounded to subangular, and silt is notably absent. 

 As the sand reposes at a high angle it possesses a curious mobility 

 which causes it to flow down the incline like soft pitch or mo- 

 lasses; the sand above the point of disturbance falls into the 

 depression and this depression advances up the slope at the same 

 time. This downward flow takes place spontaneously whenever 

 the sand, forced up the incline by the violent winds, accumulates 

 in such quantity as to exceed the angle of rest. The movement 

 is accompanied by a strong vibration and by a musical tone re- 

 sembling the lowest bass note of an organ with a tremolo stop. 

 The larger the bulk of sand moved the louder the sound ; it is 

 by no means so sensitive as the sand of so-called singing beaches 

 (which the author has described elsewhere), and fails to emit 

 sounds when struck with the hand or clapped together in a bag. 

 The vertical cliffs on either side yield an echo that may magnify 

 and prolong the sounds, which were loud enough to be heard 

 several hundred feet. The peak of Jebel Nagous rises above the 

 slope to the height of 955 feet above the sea level. The Bedouins 

 of the region account for the acoustic phenomenon by attributing 

 it to the Nagous or wooden gong of a subterranean monastery in 

 the heart of the mountain, and claim that the sounds can only be 

 heard at the hours of prayers. 



Several other sandbanks presenting a similar appearance to the 

 eye were tested but gave out no musical sounds whatever. Micro- 

 scopical examination of these sands shows that they contain much 

 silt, which prevents the vibrations necessary to yield the sounds. 

 Further, the author after testing many sandbanks on the journey 

 northward to Suez, discovered banks of sonorous sand resting on 

 low cliffs a quarter of a mile long at Wadi Werdan about a day 

 and a half from Suez, by camels, on hillocks called Ojrat Ramadan. 

 The sand blown from the extensive plains to the north, falls over 

 the southern face and rests at two angles, 31° at the top and 21° 

 or less near the base. Wherever it possesses the mobility before 

 described it emits a distinct musical note on being disturbed. 

 The highest bank measures only sixty feet on the incline, and it 

 is not probable that the sounds can occur spontaneously. Dr. 

 Julien hnds that at the new locality named by him Bolton's Bell 

 Slope, the sand is chiefly quartz, with a larger proportion of cal- 

 careous sandstone than at Jebel Nagous. The size of the grains 

 of quartz varies from 0*11 to 0*42 mm and of sandstone O'll to 

 0*34 inm , the average being smaller than that of the sand grains on 

 Jebel Nagous. Like the latter it is very free from silt. 



After alluding to the various hypotheses advanced by different 

 authors to explain the phenomena described, the author goes 

 on to mention the explanation arrived at by himself and Dr. 

 Julien. The cause of sonorousness in the sands of singing beaches 



