90 



DR. A. HOLMES OX THE PRE- CAMBRIAN [vol. lxxiv, 



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Mozambique, consist of banded and foliated gneisses accompanied 

 by crystalline schists and limestones, and penetrated by later 

 granites and pegmatites. 



The formation of the intermont plains has been accounted for 



in turn by each of the 

 three dominant processes 

 of degradation — wind- 

 scour and dry weathering 

 during desert or arid 

 conditions ; marine ero- 

 sion during an advance 

 of the sea ; peneplanation 

 during the course of the 

 ' normal geographical 

 cycle ' under conditions 

 of pluvial erosion. As 

 the chief exponent of the 

 desert theory, Passarge 

 has distinguished a 

 number of types. In the 

 B a n da type, represented 

 in Western Australia as 

 well as in Africa, the 

 level surface of the plain 

 is ascribed to a general 

 weakening of the winds, 

 whereby overdeepened 

 basins, which tend to 

 form in the absence of 

 rain, have been filled up 

 with sand. The Kor- 

 dof an type requires the 

 aid of a slight rainfall, 

 just sufficient to stem 

 the undue growth of 

 wind-scoured depressions. 

 In the Adamawa type, 

 the rainfall is now rather 

 more abundant ; while 

 in the P ovum a type 

 (German and Portuguese 

 East Africa) the plain 

 of erosion is clearly pre- 

 Cretaceous, and is held to be, at least in form, a relic of desert 

 conditions during the Mesozoic Era. According to Passarge, 

 desert erosion then controlled the topographic evolution of wide- 

 spread areas, even more extensive than those of the present day. 

 The inselberge themselves are stated to consist of resistant igneous 

 rocks such as granite, or metamorphic rocks such as quartzite. 

 The plains, on the contrary, are formed of less resistant rocks, 

 such as gneiss, schists, or sedimentary deposits. 



