216 Annals of the Carnegie Museum. 



Resume of Major Features. 



In structure, the Brazilian Complex is in nearly all places closely 

 folded, and in restricted areas contorted; and probably it has also 

 been extensively faulted. On the whole the dip and strike of the 

 foliation planes of its gneisses and schists are fairly constant over 

 considerable areas, and it seems probable that the major folds can be 

 worked out with a fair degree of accuracy, without excessively tedious 

 study on the field. 



The distribution of the Ceara Series and the areas occupied by it 

 are at present very imperfectly known; chiefly because of the simi- 

 larity of the schists of this series with the crystalline schists. Detailed 

 study will, however, probably develop criteria by which distinction 

 can be made in the field. 



The granites, have not been studied sufficiently to warrant state- 

 ments as to whether or not they represent more than one period of 

 intrusion, nor as to whether they are intrusive in both the Brazilian 

 Complex and the Ceara Series, or only in the former. The difficulties 

 involved in the elucidation of this problem are probably very similar 

 to those encountered in studies of similar complex formations in the 

 Sierra Nevada of California and in New England. 



Minor Features. 



In addition to the problems presented by the structure in the 

 Brazilian Complex, by the distribution of the Ceara Series, and by 

 the nature of the granitic intrusions, which seem to the writer to be 

 major features of the geology of Northeastern Brazil, there are three 

 minor subjects which especially attracted his attention. These are 

 the presence of quartz-gravels, widely distributed over the bedrock 

 surface, the comparatively rare occurrence of basic igneous rocks, 

 and the scarcity of springs, especially springs of thermal or of notably 

 mineralized water. 



Quartz-Gravels. Throughout the region discussed in this paper 

 there are narrow belts and wider, more scattered, deposits of gravel, 

 composed almost entirely of subangular to well-rounded fragments of 

 quartz. In many places the source of the material is apparent in 

 neighboring beds of quartzite, veins of quartz, or dikes of pegmatite, 

 the material evidently being residual from the disintegration of ledges 

 of these rocks. In other places, however, no such connection is clear. 



