[Annals N. Y. Acad. Sci., Vol. XIT, No. 8, pp. 187 to 340, Dec. 18, 1899.] 



A CONTRIBUTION TO THE GEOLOGY OF THE 

 NORTHERN BLACK HILLS. 



John Duer Irving. 



(Read March 20, 1898.) 



[Plates V-XVI ; Text Figures 5 to 20.] 

 CONTENTS. 



PAGE 



I. INTRODUCTION— Location and generalities 188 



II. TOPOGRAPHY — Details and relations to geologic structure 190 



III. STRATIGRAPHY 195 



A. Descriptive 196 



1. Algonkiau 196 



2. Cambro- Silurian 198 



3. Carboniferous 20 1 



B. Hypotheses regarding history of region 202 



IV. ERUPTIVE ROCKS 204 



/. Structural and dynamic relatio7is of erttpiive rocks. 



A. Descriptive 204 



(a) Algonkian intrusions 204 



((^) Cambrian intrusions 209 



1. Laccolites 209 



2. Sheets 229 



3. Dikes 232 



(c) Carboniferous intrusions 232 



B. Comparison between intrusions 234 



C. Views of previous writers 238 



D. Conclusions 241 



2. Petrog^raphy of eruptive rocks. 



A. Summary 244 



Of post- Cretaceous age. 

 Grorudite family. 



1. Quartz-segirite-porphyry 248 



Phonolite family. 



2. Tinguaite 257 



3. Phonolite 259 



4. Trachytoid phonolite 260 



(187) 



