Note on the Rocks of Dar ‘Ur. 209 
recognizable lithological type, and it is their presence at Jebel 
Waled, where they are being quarried for building purposes, that 
makes it possible to trace there an extension to the east of this 
series of sediments. 
West of Abiad, the “cathedral peak’ country is succeeded 
by 30 or 40 miles of “goz”’ country, rolling sandy hills among 
stretches of level plain, in which the sands are sometimes pebbly 
and hard and clad more with scrub and grass than with bush. 
Crossing the sandy “ goz”’ belt, the track enters a new type of 
rocky hill country within 30 or 40 miles of El Fasher. The 
view looking south-west and north-west from a kopje 3 miles north 
- of Juga-Juga shows a few low conical hills projecting here and there 
from a vast sandy plain, with hill-ranges in the far distance. Here 
the country seems to be formed of metamorphic rocks. Fragments 
of pink and green epidotized aplite (28) were noticed in the * khors ” 
round Juga-Juga. Specimens from one of the low conical hills, 
“boulder kopjes,” are of brotite-qnerss (30) and. biotite- amphibolite 
(29). The latter is a fine-grained, equigranular, dark-green rock, 
and consists of brown biotite and green hornblende, with acid 
oligoclase, some orthoclase, and quartz. The accessory minerals 
are magnetite (or ilmenite) and apatite in small crystals. Nine miles 
south of El Fasher a vein of compact white quartz (27) forms the top 
_ of a small “ kopje”’, 120 feet above the level of the plain. 
Jebel Marra lies some 70 miles W.S.W. of El Fasher. It is a large 
mountain mass, extending perhaps 50 miles north and south and 20 
east and west, with much of its area at a mean elevation of 8,000 feet 
above sea-level. It forms the dominant mountain-group between the 
Abyssinian Plateau and the mountains of Nigeria and the Cameroons, 
while in a north and south direction the nearest high features are 
the great Equatorial mountains on the one hand, and on the other 
the Tibesti Range, with the high ground round Mount Durbulla 
as a sort of connecting-link. The part of these mountains visited 
was the extreme southern end of the upper zone, where is an extinct 
volcano with a soda-lake, Lake Dereiba, on the crater-floor at 
7,500 feet, and with peaks on the crater-wall rising to 10,000 feet 
above sea-level. 
The route taken from El Fasher to Jebel Marra skirted the 
mountain system, passing up a more or less gradual ascent, through 
a heavy sandy belt, to a rocky country and the outlying hills of the 
Jebel Marra system itself. Here foothills of fantastic shapes fringe 
all the eastern base of the massif. The vegetation grows more 
succulent as one gets south, until at Kallokitting, 4,000 ‘feet, at the 
beginning of the main ascent, there is perennial - water in the Wadi 
Ghindi and quite rich vegetation wherever the water or moisture 
rises to the surface. 
An outlying foothill between Darweis and Kallokitting consists 
of biotite-granite rich in oligoclase, of which two specimens were 
collected (25). A large slab of the same kind of granite was seen at 
VOL. LYIII.—No. V. 14 
