22 TRANSACTIONS OF THE [OCT. 21, 



1888, and May 13th, 1889. In tliese papers the occurrence of 

 sonorous sand on beaches in America and Europe, its physical 

 properties, and the acoustic phenomena characteristic of it, were 

 detailed. In the present communication, Dr. Bolton reported 

 the result of a personal investigation of the sonorous sand in the 

 Desert of Arabia Petrtea, especially at Jebel Nagous on the Gulf 

 of Suez. 



After describing the proximate starting-point for Jebel l^agous, 

 "the little village of Tor, and the surface geology of the vicinity, 

 the speaker detailed his experiences at the " Mountain of the 

 JBell,'^ so-called. This mountain is situated about 44^ hours N. W. 

 of Tor, on the Gulf of Suez. On its steep sides rest several 

 large banks of sand ; one of these, which I distinguish by the 

 name Seetzen's Bell Slope, after its discoverer, emits distinct 

 musical souuds whenever the sand slides down the incline, either 

 spontaneously or through the agency of man. The mountain 

 consists of massive white sandstone carrying quartz pebbles and 

 veins ; it is about three miles long and 1/200 feet high. The 

 huge Bell Slope measures 260 feet across the base, 5 or G feet 

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

 vertical walls of sandstone. The sand rests on the rocks at the 

 high angle of 31°, and is very fine-grained, yellowish-white, 

 and composed chiefly of quartz and calcareous sandstone. The 

 grains are well rounded to subangular, and silt is notably ab- 

 sent. As the sand reposes at a high angle, it possesses a 

 cnrious mobility which causes it to flow down the incline like 

 8oft pitch or molasses ; the sand above the point of disturbance 

 falls into the depression, and thus the 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 vibra- 

 tion and by a musical tone resembling 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, 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 which may magnify 

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

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

 the Slope to the height of 955 feet above the sea-level. 



The sand of the Slope is derived partly from disintegration of 

 the rock itself, and partly from the more distant plain below, 

 from which violent winds blow it up on to the mountain side. 



The Bedouins of the region account for the acoustic phenome- 

 non by attributing it to the Nagoiis, or wooden gong of a subter- 



