NEWTON S MAP OF THE BLACK HILLS NUCLEUS. 



205 



Very numerous specimens were collected, from which thin sections have been 

 made. The objects of the study were, to ascertain the basis upon which these 

 rocks are divided into two series; to get, if possible, some idea of their 

 structure; to compare them with those of other pre-Cambrian areas; and, 

 finally, to attempt to get at the genesis of the crystalline schists there exposed. 



i-)!r v J Granite 



S*:SSSa Modern Volcanics 



Carboniferous 



Cambrian 



Slate. 



Schist 



Scale of Miles. 



OS 4 O S JO 32 14 IB 



> > ' I i I t 1 I 



A Portion of NEWTONS MAP"™* BLACK HILLS. 



Figure 1. 



