Geology and Palcontology. 835 
of but one, viz.: a simply quadritubercular, and a specialization of 
it where the tubercles are connected together by crests. For the 
£ aleontologie, II, Band, Zweites Heft., 1888. 
Petermann’s Geographische Mitteilungen, XXXIII., 1887, 
Sea, and Guinea coast districts; the Palæozoic, which as colored 
includes the Dyas in the Atlas Mountains, but excludes that 
formation elsewhere, is prominent only in patches of the Sahara, 
and in South Africa; the Karroo-formation, which in the sou 
includes Dyas and Trias, covers all South Africa save the portions 
occupied by the crystalline and palæozoic rocks, and reappears in 
large patches on the eastern and western coasts, as well as in the 
iger region; the Cretaceous is most conspicuous in the north, 
Where it occupies the greater part of the Barbary States west of 
Barea ; and the Tertiary strata cover the entire lower Nile valley, 
and stretch along the Mediterranean west to the Gulf of Sydra. 
From the head of the eocene to Khartum cretaceous rocks are 
Shown bordering the Nile. The principal mass of the younger 
