February 19, 1920] 



NATURE 



66 



/ 



THE "TIMES" AFRICAN FLIGHT. 

 Discovery of a New Volcanic Field. 



NEWS has been received with great disappoint- 

 ment that, owing to the failure of the 

 engine, Dr. Chalmers Mitchell's trans-African 

 flight was checked on February 1 1 , when a 

 descent had to be made in the bush, and then 

 the machine was taken to Jebelein for repairs. 

 The South African machine, the Silver Queen, 

 has been irreparably smashed by a forced descent 

 at night at Korosko. The troubles of both 

 machines may be due to their having been unduly 

 forced, owing to the supplies of petrol in some 

 southern stations being apparently adequate for 

 one machine only. The flight was resumed on 

 February 14, and a point twenty miles from 

 Mongalla was reached at 4 p.m. on that date. 

 On the following day the short flight was taken 

 to Mongalla, where Dr. Chalmers Mitchell 

 expected to be detained for three days. In his 

 latest message, dated February 16, he says : — 



I consider the Cairo-Khartum part of the route 

 satisfactory if relays of aeroplanes are available. The 

 arranged landing-grounds are good and forced descents 

 fairly practicable. The stage from Khartum to Mon- 

 galla is extremely dangerous, as the arranged aero- 

 dromes are difficult to locate and forced descents re- 

 quire luck and unusual skill. Bush fires destroy 

 visibility, and render the smoke fires on the aero- 

 dromes useless as guides. The positions of the wire- 

 less station and the telegraph wires at Mongalla are 

 extremely dangerous. The pilots, the mechanics, and 

 the Vickers' "Vimy" machine are excellent. We 

 hope that the worst of the trip is over, but must 

 proceed slowly. 



Dr. Chalmers Mitchell has thus successfully 

 achieved more than one-third of the journey 

 along Africa, and has shown how valuable aero- 

 plane surveys may be by a discovery of first-class 

 importance. After leaving Assuan, on approach- 

 ing the section of the Nile flowing from south- 

 west to north-east from Dosha to Korosko, he 

 remarked many high hills with steep walls running 

 north-east and south-west. These steep hill- 

 fronts may indicate that both the section of the 

 Nile above Korosko and the parallel section from 

 Korti to Abu Hamed were determined by earth- 

 movements, which have a wide influence in this 

 part of Africa ; for the section of the Nile flow- 

 ing from Abu Hamed south-west to Korti is in 

 line with a remarkable breach through the moun- 

 tain rim of the Red Sea basin. The mountains 

 which extend west of the Red Sea from behind 

 Kosseir, southward past Berenice and Mersa 

 Shab, end to the south-east in the group of Adal 

 Qaqa (about 5925 ft.). The geology of this group 

 is known by the monograph by Dr. J. Ball (1912), 

 whose maps indicate the existence of faults of late 

 Cretaceous or post-Cretaceous age, some of which 

 trend north-west to south-east, and others from 

 north-east to south-west. South-east of Adal 

 Qaqa the highlands are resumed by the moun- 

 tains which extend south from Gebel Elba, west 



NO. 2625, VOL. 104] 



of Cape Elba, through Gebel Shendil (6275 ft.) 



and Gebel .Vsotriba (7270 ft.). The .'\dal Qa^a 



I and the south-eastern groups are separated by a 



; deep depression formed by the plains of Nafab 



I and by the broad valley of the Wadi Di-ib which 



I discharges to the Red Sea. The divide between 



} the Nafab and Wadi Di-ib is probably less than 



2000 ft. above sea-level. The straight course of 



the looo-metre contour line on the south-eastern 



side of the .\dal Qaqa group, as shown on the 



I : 7,500,000 map of the Nile Basin by the 



Egyptian Survey (1906), occurs on the extension 



of the line of the Nile from Abu Hamed to Korti. 



On the continuation of this line across the Red 



Sea the irregularities in the front of the Arabian 



plateau between the coastlands of El-Gof and 



Medina may be due to the same tectonic cause. 



The representation of the looo-metre contour 

 near Adal Qaqa may be untrustworthy, or its 

 continuation on the line of the Nile from .A^bu 

 Hamed to Korti may be only a coincidence. But 

 the probability of a long north-east to south-west 

 fracture is strengthened by the discovery by the 

 Times Expedition of a group of extinct volcanoes 

 in the Bayuda Desert, half-way between Merowe 

 and Berber. 



The discovery is quite new, since this volcanic 

 field was unknown to so alert an observer as Mr. 

 G. W. Grabham, the Government Geologist of 

 the Sudan. Mr. Grabham has, however, been 

 able to support Dr. Chalmers Mitchell's identifica- 

 tion, as he had received some volcanic tuffs 

 obtained by Sir Herbert Jackson about fifty miles 

 distant from the craters seen by Dr. Chalmers 

 Mitchell. There was apparently no evidence as 

 j to the age of these tuffs, or whether they came 

 i from modern volcanoes, but Dr. Chalmers Mitchell 

 concludes from his observations that the erup- 

 ] tions were not later than the Kainozoic, and as 

 j he refers to the hills as craters they were probably 

 ' formed late in that era. The great earth-move- 

 ments along the Rift Valley are frequently asso- 

 ciated with volcanic outbreaks, due to material 

 compressed by the subsidence, being forced up 

 j the adjacent fractures. Dr. Chalmers Mitchell's 

 I discovery, therefore, suggests that one line of 

 j crustal fractures explains the bend of the Nile 

 I south-westward from Abu Hamed to Korti, the 

 ; Nafab — Di-ib depression, and the Bayuda 

 volcanic field. 



Col. Lyons has shown that the course of the 

 Nile from Berber to Korosko is comparatively 

 young, and that above Berber, as at the Shabluka 

 Gorge, it has re-excavated a new channel through 

 the comparatively soft rocks which have filled up 

 an older valley. It therefore seemed possible, 

 from the information previously available, that 

 the disturbances which have given the Nile its 

 S-shaped course from Korosko to Khartum were 

 due to earth-movements contemporary with the 

 breach through the Red Sea rim near Berenice. 

 This conclusion is strengthened by the discovery 

 of the Bavuda volcanoes. The movements doubt- 



