160 Messrs. Ban-on 8f Hiuiie — Eadern Desert of Egypt. 



central range, dolerites and other basic rocks are seen capping some 

 of the highest granite hills, still remaining as a thin coating, which 

 otherwise has been almost entirely removed by denudation. Again, 

 the base of the same range is fringed by a belt of the same character, 

 the presence of which is probably directly referable to faulting on 

 a large scale. 



South-west of the central range, too, extends the Fatiri El Iswid 

 district, consisting of range after range, in which dolerites, serpentines, 

 compacted ashes, now practically slates, and agglomerates play an 

 important part. While on the south of lat. 27° N. these rocks 

 only give rise to low hills of complex character, to the north 

 of that line they take part in the formation of scenic features of 

 the first magnitude, rising to 1,800 metres in Jebel Dokhan, and 

 composing some of the principal longitudinal ranges forming the 

 eastern boundary of the Red Sea Hills. 



The members of this volcanic series are of somewhat different 

 character from those previously mentioned, dark andesites being as 

 conspicuous as the dolerite sheets associated with them, while the 

 sheared diabases have been replaced by tuffs and asbes far less 

 compact than those near Qosseir. The agglomerates, too, are very 

 striking in the El Urf chain, where blocks of ' imperial porphyrj'^ ' 

 ai-e included among the rock fragments. Indeed, the most interesting 

 member of this series is the imperial porphyry of Jebel Dokhan, 

 typical specimens of which are withamite, containing andesites, 

 though the same mineral is present in some of the tuffs. 



Relative Age of the Volcanic Series. — It has already been 

 stated that the dolerites, diabases, etc., rest upon the Metamorphic 

 Schists and Gneisses, and are younger than the latter, but it 

 is equally possible to show that the giieissose granites and 

 diorites, which underlie them over wide areas, are of still later 

 date. Thus, to take a few typical cases, a mass of mica-diorite has 

 been intruded into the agglomerate, while in Wadi Esh, near 

 Qosseir, the sides of the valley are formed of grey granite which, is 

 overlaid by the compact dolerite, but the former has sent numerous 

 veins into the latter. Other examples will be mentioned in the 

 report, but one of the best is close to the pass leading from AVadi 

 Um Sidri to Um Messaid, where a dyke of red microgranite in the 

 andesite has for a time prevented another vein of grey granite from 

 penetrating into the lava, but finally, after running parallel for 

 a short distance, the latter lias succeeded in bursting through, and 

 has sent long veins and branches into the porphyry. 



Granites. — The rocks of granitic character in the Red Sea Hills 

 are sharply divided into two groups, giving rise to very different 

 types of scenery. The most prominent variety is a coarse red 

 granite, poor in mica, which forms some of the finest summits north 

 of and on the latitude of 27 degrees N., these being usually 

 characterized by steepness, the mountains being seamed by bouldery 

 ravines which cause the crests to have a highly serrated outline, 

 while nearly all the lower country consists of bouldery ridges of 

 a gneissose biotite, or hornblende granite, which, has its south-eastern 



