NA TURE 



THURSDAY, DECEMBER 6, iS 



THE GEOLOGY OF THE LIBYAN DESERT 



Beitrd^e siir Geologie und Palceontologie der Libyschen 

 Wiiste und der angrcn^ciidcn Gcbietc voti /Egyploi, 

 un/er MHwirkiiig 7nchrercr Fachgenossen, lierausgegebeii 

 von Karl A. Zittel. I Theil und II Abtheilung, i Heft. 

 (Contributions to the Geology and Palaeontology of the 

 Libyan Desert and of the Neighbouring Districts of 

 Egypt. By Karl A. Zittel, with the assistance of 

 several scientific men. Part I. and Part II., Section i.) 

 (Cassel : Fischer, 1883.) 



IN Nature, vol. xxii. p. 587, there appeared a notice 

 of the anniversary address for that year to the 

 Academy of Natural Sciences in Munich delivered by 

 Prof Karl A. Zittel, the well- known Professor of Geology 

 and Palaeontology at the Munich University. The 

 address contained a preliminary sketch of the work, the 

 complete account of which occupies the quarto volume 

 and portion of a second vohune now before us. 



In the winter of 1873-74 a scientific expedition under 

 the leadership of Gerhard Rohlfs was despatched with aid 

 from the late Khedive of Egypt, Ismail Pacha, to explore 

 the Libjan desert or north-eastern portion of the Sahara. 

 The scientific results of this expedition are now being 

 published in a series of separate volumes, of which the 

 Geology and Palaeontology will form two. The first of 

 these lies before us, the second is as yet incomplete, and 

 only one section containing a description of the Eocene 

 Echinoidea, by P. de Loriol, has hitherto appeared. The 

 first volume comprises the geological description of the 

 country by Prof. Zittel himself, an account of the fossil 

 wood from the Nubian sandstone and from the well- 

 known "fossil forest" near Cairo (Cretaceous), by Dr. A. 

 Schenk ; of the Miocene fauna of Egypt and the Libyan 

 desert, by Dr. Th. Fuchs ; of the Tertiary (Upper Eocene 

 or tiligocene) fossils from the western island in the lake 

 of Birket-el-OurCin (about fifty miles south-west of Cairo), 

 by Prof. Karl Meyer-Eymar ; of the Foraminifera (the 

 Nummulites excluded) from the Eocene beds of the 

 Libyan desert and Egypt, by Conrad Schwager; a mono- 

 graph of the Nummulites from the same areas, by the 

 late Dr. Phil, de la Harpe ; and a description of the 

 Eocene corals, by Magister E. Pratz. These palasozoic 

 descriptions are illustrated by thirty-six plates. 



The remaining portions of the second volume will in- 

 clude an account of the Eocene Mollusca, by Prof Meyer- 

 Eymar ; of the Cretaceous fauna, chiefly by Prof Zittel 

 himself ; and of a few other subjects. Amongst the con- 

 tributors, besides those already enumerated, the names of 

 Prof. Beyrich, the Marquis de Saporta, Prof Haushofer, 

 and Prof Zirkel are mentioned in the preface to the first 

 volume. 



An array of scientific names like the above, chosen 

 from amongst the most eminent specialists of Germany, 

 Switzerland, and France, proves that this is a work of 

 more than ordinarj' geological importance. The prin- 

 cipal author and editor. Prof Zittel, is both a good geolo- 

 gist and a good palaeontologist, a much rarer conrbination 

 than is usually supposed. 



Vol. XXIX. — No. 736 



On the geological map in the first volume an area 

 occupying rather more than 5' of latitude (25' to 30° N.) 

 and above V of longitude (about 25° 30' to 33" 40' E.) is 

 coloured. This country includes the Nile valley from 

 Cairo to Edfu (the geology of the valley itself is shown as 

 far south as .Assuan), and extends eastwards to the shores 

 of the Red Sea, and westward far into the great desert 

 tract of Northern Africa. The whole area coloured geo- 

 logically may be roughly estimated at between 150,000 

 and 160,000 English square miles. 



It will easily be understood that the mapping is of a 

 very rough description, a geological sketch in fact, but in 

 desert countries, owing to the want of vegetation to 

 conceal the rocks, and to the clearness of the atmosphere, 

 it is remarkable with what accuracy geological formations 

 can be traced by the eye to great distances. A considerable 

 proportion of the area is coloured from the observations 

 of other travellers, and especially of Schweinfurth. The 

 routes of the expedition under Rohlfs and of other tra- 

 vellers are marked on the map, and show how much of 

 the area has actually been examined. 



Among the numerous points of interest presented by 

 the volume it is difficult to select any one as superior to 

 the others. In the former notice in N.\ture the general 

 characters of the geological systems observed (Cre- 

 taceous, Eocene, Miocene, and the so-called Quaternary 

 and recent) were briefly described. To enter at any 

 length into a notice of the palaeontology would take too 

 long. At the present time when the writings of F. von 

 Richthofen and others have called especial attention to 

 the subierial or Eolian formations of the latest geological 

 times and the present day, the description of the surface 

 phenomena presented by the desert tracts of the Sahar.\, 

 coming from so keen an observer as Prof Zittel, are well 

 worthy of attention, and a few remarks upon them may 

 prove interesting. 



The geological portion of the work is divided into two 

 chapters : thefirst,containingforty-two pages, being devoted 

 to the Sahara as a whole ; the second to the geology of the 

 Libyan desert and Egypt. In both of these chapters con- 

 siderable space is devoted to the superficial characters of 

 the desert. The surface of the Sahara is divided by Prof 

 Zittel, according to its characters, into four kinds : — (i) 

 Plateau-desert or Hammada, occupying the largest por- 

 tion of the area, a level, hard, stony surface in general, 

 without noteworthy elevations or depressions, but passing 

 locally into (2) mountainous desert. The so-called (3) 

 erosion-desert consists of depressions more or less occu- 

 pied by salt-marsh. The last form of surface, the most 

 remarkable and interesting of all, is the (4) sandy desert 

 or Areg, composed of drift sand forming hills or downs 

 (dunes). 



Prof Zittel shows, on what appears to be an over- 

 whelming amount of evidence, that the popular idea of 

 the Sahara having been the basin of a sea in Pleistocene 

 times is without foundation. The greater part of the area 

 has apparently been above water ever since the Cretaceous 

 epoch ; a comparatively small tract in the north-eastern 

 portion was submerged beneath a Tertiary sea, whilst the 

 only part that can have been under water in post-Tertiary 

 times consists of a tract extending from the Nile delta to 

 the oasis of Amnion, and to the so-called "Chotts" of 

 Tunis, and even in this tract marine conditions in late 



