

BY H. I. JENSEN. 545 



C. Africa. 



The coastal zone of Morocco and Algeria is composed chiefly of 

 volcanic rocks amongst which alkaline lavas play a prominent 

 pai't. They are mostly of early Tertiary age. The lavas overlie 

 upturned schists, granites, and phyllites which belong to the 

 Pelitoranian massive. This massive was continuous from North 

 Africa, across Malta and Sicily, to Sardinia in Mesozoic times, 

 and was fractured and broken up after the Cretaceous. It con- 

 stituted the Vorland against which the Cretaceous sediments of 

 the Atlas Mountains were folded. 



Behind the volcanic zone we have the Atlas region of Mesozoic 

 sedimentation, and on the southern border of the Sahara com- 

 mences the real African massive. In the folded Atlas Range 

 alkaline rocks do not seem to have been met with, but on the 

 border between the Saharean area of Mesozoic sedimentation and 

 the old fractured African continent they have been noticed, as at 

 Lake Tschad, Kordofan, etc. Again, they occur in the Cape 

 Verde Islands superimposed on subsided fragments of the African 

 continent; and further foyaites occur in the Los Archipelago, and 

 olivine gabbro at Freetown (Sierra Leone), apparently interstra- 

 tified with horizontal sedimentary beds. The latter consist of 

 red sandstone and interbedded shales overlying Archaean rocks, 

 and were probably deposited at the time of the Jurassic trans- 

 gression which affected a great part of Africa. To my mind it 

 is highly improbable that these rocks are altered interstratified 

 lavas, inasmuch as they are called gabbro and foyaite, names 

 applied to coarse-grained hypabyssal rocks. They are probably 

 true sills or laccolites of Post-Jurassic age. 



Alkaline trachytes and allied foyaitic rocks have been recorded 

 from Transvaal, and the Drakenberg Mountains, between Natal 

 and Transvaal, are principally volcanic. This part of the world 

 has undergone no movements involving folding or horizontal dis- 

 placement since early Palaeozoic time. Faulting has, however, 

 been very extensive, and has been accompanied by considerable 

 vertical movements. Throughout the late Palaeozoic and Mesozoic 

 periods South Africa was a portion of Lemuria. Absence of 



