98 J. C. BRANNER GEOLOGY OF NORTHEAST COAST OF BRAZIL 



12. The most striking topographic features of the region traversed by 

 the railway are : 



The enormous sand dunes on the plateau southwest of Natal. 



The flat bottoms of the valle} T s cut in the Tertiary (?) sediment, show- 

 ing a comparatively recent depression of the coast. 



In many instances these valleys are still in process of filling up. The 

 great Mipibu lake is in one of these depressed valleys. 



