OP THE HALOLIMNIC FAUNA OP LAKE TANGANYIKA. 351 



Part II. 



Outlines of African Geology with Especial Eeference 

 TO THE Central Eegions i.nt which Lake Tanganyika 

 IS Situated. 



It need hardly be observed that Africa is an extensive 

 though well-defined continent, and from its size it might be 

 expected to exhibit considerable variety of rock formation. 

 Yet this is by no means the case, since the proportion of 

 crystalline rocks and barren sandstones is so great that it& 

 life history has been, for the most part, but obscurely written. 

 If the medals of creation were ever struck here in any con- 

 siderable quantity they have since been in a great measure 

 destroyed. The absence of fossil evidence is especially 

 noteworthy in the equatorial regions, which form the special 

 ground of our inquiry. 



Eoughly speaking for geological purposes the whole of 

 Africa might be divided into three divisions of very unequal 

 size. 



(1) The Northern Division. — This may be considered as part 

 of the Mediterranean basin, and indeed, almost as European 

 for geological and orogenic purposes, always regarding the 

 Atlas range and its dependencies as being under the same 

 tectonic system as the Alps. Although the precise boundaries 

 of this division can scarcely be defined, it is a limited area and 

 by no means deficient in marine fossiliferous rocks. In Part I, 

 under the heading of Algeria and Tunisia, some of the 

 palasontological features of this division have already been 

 indicated. Marine beds of Mesozoic and Tertiary age constitute 

 the bulk of these rocks. Morocco may be included in this 

 category. 



(2) The Region of the Great Deserts constitutes the principal 

 part of the second division. Prof. Cornet* tells us that this- 

 is characterized by the horizontality of the palaeozoic beds, as 

 though the area had not been one of disturbance for a long 

 period. He also says that there is a great hiatus in the 

 formations of this region, extending in time from the Car- 

 boniferous to the Cretaceous. 



* " Formations postprimaires du bassin du Congo," Ann. Soc. Ge'oL 

 Beige, vol. 21 (1893-4). 



