176 Mevieivs — Prof. Dr. Karl ZitteVs Geology and 



1. The Cretnceous System. — The Cretaceous system of the Libyan 

 desert can be divided into four series. 



I. The Nubian sandstone, which is the ohlest sedimentary rock 

 west of the Nile. It was largely employed in the gigantic temples 

 of Upper Egypt and Nubia, and the mighty Memnon Colossi of 

 Thebes ; and its regular bedding and the presence of thin bands 

 of soft clay and marl greatly facilitated the excavation of enormous 

 monoliths and cubical blocks. In the neighbourhood of Assuan, 

 this sandstone rests on granite and its lowest beds consist almost 

 everywhere of small quartz pebbles in a matrix of a kaolinic material. 

 The only fossils discovered in this sandstone are fragments of wood 

 belonging to two species, Nicolin ^gijptiaca, Ungei", and Araucari- 

 oxylon (Dadoxiilon) JEgyptiacum, linger, sp. There is no doubt of 

 the identity of this sandstone in Assuan, Nubia, and the Libyan 

 desert, and that it is of Middle or Upper Cretaceous age ; most pro- 

 bably the equivalent of the Cenomanian. Very various opinions have 

 been put forward by different oliservers as to its age, arising from the 

 fact that it has been confounded with strata of similar petrogi'aphical 

 characters in Palestine, the Peninsula of Sinai, and Abyssinia. The 

 Abyssinian sandstone has been described by Blanford as either 

 Permian or Triassic, and from some imperfect fossils found in the 

 Sinaitic strata it is probably of Carboniferous age. It follows, there- 

 fore, that the term " Nubian " sandstone should be restricted to the 

 beds exposed in Nubia, Assuan, and the Libyan desert. 



II. Strata with Exogyra Ooerwegi. These consist of beds of 

 marl, clay, and limestone, with rock-salt and gypsum, in all about 

 150 m. in thickness. Fossil wood, fish teeth {Otodiis and Lamna), and 

 shells of Exogyra and Inoceramiis, and also of Ammonites, occur in 

 this division. 



III. Greenish and Ashy-grey Laminated Clays. These vary 

 from 30 to 80 m. in thickness. The beds in places are even black 

 in tint, and are always bituminous and gypsiferous. The fossils 

 are distinctively of Upper Cretaceous age, and though the species 

 are not very numerous, yet the individuals are so abundant that in 

 places the surface is completely covered with their casts in iron 

 oxide.- 



IV. Snowy-white bedded Limestone or Earthy Chalk. This 

 summit division of the Upper Chalk varies from 20 to 50 m. in 

 thickness; it frequently forms vertical walls bordering the summits 

 of the hills and plateaux. In some localities it is nearly entirely 

 composed of Coccoliths and Foraminifera {Textulnria, Cristellaria 

 and Botalia), as well as larger fossils, some of which, particularly 

 Gasteropoda, bear a certain resemblance to Eocene forms. The 

 presence of Ananchytes ovaia and Ventriculites, as well as other 

 Upper Chalk fossils, clearly defines its geological horizon. 



The Upper Chalk of the Libyan desert is characterized not only 

 by its great development of over 400 metres in thickness, but also 

 by its varied petrographical characters, and its astonishing richness 

 in well-preserved fossils. It is probable that when the fossils are 

 fairly well known, the North African facies of the Upper Chalk 



