BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 VOL. 1, PP. 203-244,, PLS. 4, 5 MARCH 26, 1890 



THE PRE-CAMBRIAN ROCKS OF THE BLACK HILLS. 



BY C. R. VAN HISE. 

 [Read by title before the Society December 28, 1889.) 



CONTENTS. 



Page. 



Previous Work 203 



Scope of Paper 204 



Distribution and Structure of the Bocks . 20G 



Origin of the Granite 210 



Age of the Granite 212 



Permanency of Clastic Characters in Rocks 218 



Lilhological Divisions _i 214 



The Conglomerates and Quartzites 215 



The Mica-slates and Mica-schists 222 



The Mica-gneisses 226 



Garnet, Staurolite, and Tourmaline 227 



Other Crystalline Rocks 220 



Nature of Original Sediment 230 



Bearing of Microscopical Study upon the Origin of the Granite 231 



Bedding, Cleavage and Foliation -_. 232 



Correlation . 234 



Sum mar v of Conclusions 240 



Previous Work. 



Apparently Dr. Hayden ' ;: and Professor N. H. Winchell f were the earliest 

 geologists to visit, the Black Hills of Dakota; the former while engaged in 

 his extended surveys in the Northwest, the latter as the geologist of General 

 Custer's expedition of 1874. The works of both in this region were no more 

 than reconnaissances, and the pre-Cambriau rocks received comparatively 

 little attention. 



One of the consequences of these preliminary trips and exaggerated re- 

 ports as to the richness of the hills in gold was a systematic survey of the 



*On the Geology and Natural History of the Upper Missouri, F. V. Hayden : Trans. Am. Phil. 

 Soc, 1861, pp. 218. This was Dr. Haydeu's most complete account of the Black Hills region, and 

 sums up the results of his previous reports. 



f Geological Report on the Black Hills of Dakota, with map, by N. H. Winchell. Contained in 

 "A Report of a Reconnaissance of the Black Hills ot Dakota," made in the summer of 1S74, by 

 William Ludlow; 1875, pp. 21-60. 



XXVII— Bull. Geol. Soc. Am., Vol. 1, 1889. (203) 



