NATURE 



569 



THURSDAY. OCTOBER ic. 



1903. 



EGYPTIAN GEOLOGY. 

 Topography and Geology of the Eastern Desert of 

 Egypt {Central Portion). By T. Barron, A.R.C.S., 

 F.G.S., and W. F. Hume, D.Sc, A.R.S.M., 

 F.G.S. Geological Survey Report. Pp. viii + 331. 

 (Cairo : National Printing Department, 1902.) 



THE work before us is the largest instalment yet 

 published of the results of the explorations 

 which have been carried on with such success by 

 the Egyptian Geological Survey, under the able and 

 energetic direction of Captain Lyons. The district 

 now described was actually surveyed in the years 

 1897 and 1898, but there appear to have been many 

 delays in arranging for the publication — the time of 

 the authors being taken up by fresh work undertaken 

 in widely distant regions. At the geological congress 

 held in Paris in 1900, however, the two authors of the 

 memoir were permitted to lay some of the chief results 

 obtained from the study of this region before the 

 geologists who had assembled there, and abstracts of 

 their papers have appeared in the Geological 

 Magazine for 190 1 ; but the publication of this large 

 and well-illustrated memoir has long been eagerly 

 anticipated, and its appearance will be everywhere 

 welcomed as a most valuable addition to the scientific 

 literature of the district. 



The authors must be congratulated upon the excel- 

 lent use they have made of the vast mass of literature 

 dealing with the geology of the area. In an 

 appendix they have given an admirable abstract of 

 the results obtained by De Rosi^re, Wilkinson, 

 Schweinfurth, Klunzinger, Walther, and many other 

 travellers, who have by their writings added to our 

 knowledge of this very interesting region. The work 

 of the geological surveyors — a very important one — 

 has been that of correlating and correcting these 

 various sources of information and of supplying, by 

 actual observations in' the field, the links necessary 

 to combine the whole into a connected monograph 

 dealing both with the topography and geology of the 

 district. 



Like the work carried on in the western territories 

 of North America by the United States Geological 

 Survey, the work in the Egyptian deserts has to be a 

 combination of a geological and a topographical 

 survey. Each working party had to consist of a 

 geologist and a topographer, with a small caravan 

 consisting of eleven Arabs and fifteen camels. The 

 topographical work was done by using a measuring 

 wheel Tor determining a base line, and working from 

 this with plane-table and theodolite, frequent observ- 

 ations for latitude being made to correct the results ; 

 the heights were determined by the aneroid in most 

 instances, but in important cases hypsometer and 

 theodolite determinations were made also. The chief 

 difficulties experienced in the topographical work — 

 apart from those arising from traversing waterless 

 districts — were caused by the mirage and by the 

 frequent presence of great masses of magnetic rock. 

 NO. 1772, VOL. 68] 



While the topographers were engaged in making 

 the map as complete as possible, tht^ geologists were 

 busy examining and recording the interesting features 

 exhibited by the various rock-masses. encountered in 

 the different traverses. The district described includes 

 tho famous porphyry, quarries of Djebel Dokhan, and 

 the ancient upraised coral reefs and their modern 

 representatives on the shores of the Red Sea — some 

 of these reefs being of especial interest, owing to the 

 partial dolomitisation which they have undergone. 



The first 115 pages of the volume (which extends 

 to 331 pages) are occupied by an account of the 

 topography of the Red-Sea Hills, and in this part 

 of the work there is much matter of archaeological 

 interest in the account of the numerous remains of 

 Roman buildings, and of ancient quarrying and 

 mining works. A very excellent account is also given 

 of the meteorology and of the botany and zoology of 

 the district. 



The description of the geology which occupies the 

 second and larger half of the volume deals with the 

 Pleistocene gravels, old beaches, and raised coral reefs, 

 the Pliocene gravels, conglomerates and limestones, 

 the Miocene and Eocene limestones, marls, &c., the 

 Cretaceous limestones, and the " Nubian Sandstone," 

 which in this particular district appears to be in no 

 part older than the Cretaceous. The sedimentary 

 rocks of the district are about 2000 feet in thickness, 

 and cover unconformably the metamorphic and asso- 

 ciated igneous rocks. The latter consist of quartz- 

 diorites or grey granites which are younger than 

 and invade the metamorphic rocks, and are themselves 

 intruded into by masses of red granite, with, probably 

 associated, dykes of quartz-felsite and dolerite. These 

 rocks with veins of diabase which intersect them 

 have all been planed down by denudation before the 

 deposition of the sedimentaries. The only later 

 igneous rocks are the andesites which have been 

 intruded into the Eocene limestones, and have pro- 

 duced contact metamorphism in them, and certain 

 igneous gravels and conglomerates which unconform- 

 ably overlie the sandy limestones of Pliocene age. 



The volume is admirably illustrated. Besides the 

 general topographical map of the district and the same 

 geologically coloured, there are five geological maps 

 of areas of special interest. There are also four plates 

 containing coloured panoramas, which give an excel- 

 lent idea of the relations of the various igneous and 

 other rock masses in this region ; and the geological 

 structure of the district is further illustrated by eleven 

 plates of longitudinal sections. The general aspects 

 of this, it must be confessed, rather uninviting region 

 are shown by nine beautiful photogravures by Dr. E. 

 Albert and Co., of Munich, from photographs taken 

 by the authors, while three plates and six photographs 

 are devoted to objects of archaeological and general 

 interest. 



The important palaeontological researches of Bead- 

 nell and Andrews have attracted the attention of all 

 geologists to the important work which is being ac- 

 complished by the Geological Survey of the Egyptian 

 Government, and the present work will serve to show 

 that every branch of geological science is receiving 



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