CONTENTS. VII 



Chapter V — Continued. Page. 



Outlet Canyon 194 



Channel Mountain 196 



Flat Mountain 196 



West Base of Two Oceau Plateau '. 19" 



Two Ocean Plateau 200 



Chapter VI.— Geology of the southern end of the Snowy Range, by W. H. Weed 203 



General description 203 



Topography 204 



Sedimentary rocka 205 



Buffalo Plateau 206 



Lamar Valley 207 



Slough Creek 208 



Soda Butte Creek 210 



Pebble Creek 211 



Soda Butte Valley 212 



Chapter A r II. — The dissected volcano of Crandall Basin, Wyoming, by J. P. Iddings.. 215 



Introduction 215 



Geological description 216 



General features 216 



Early acid breccia 219 



Basic breccia and flows 220 



Distinctly bedded breccia 221 



Chaotic breccia 222 



Dikes 224 



Extent of erosion 232 



Petrography of the rocks of the district 237 



Early acid breccia 237 



Basic breccia and lava flows 238 



Basalt flows 239 



Intrusive rocks 240 



Outlying dikes 240 



Granular core and intersecting dikes 246 



Mineral and chemical variations of rocks 259 



Crystallization 265 



Development of phenocrysts 266 



Chapter VIII. — The igneous rocks of the Absaroka Eange and Two Ocean Plateau 



and of outlying portions of the Yellowstone National Park, by J. P. Iddings 269 



Introduction 269 



Early acid breccia 270 



Early basic breccia and associated basaltic flows 275 



Late acid breccia 281 



Late basic breccia 296 



Dikes and surficial flows 304 



Vicinity of Sylvan Pass 304 



Dikes south and southeast of Sylvan Pass 311 



Massive flows and intrusions of light-colored audesite 314 



Trachy tic rhyolite 321 



Chapter IX. — Absarokite-shoshonite-banakite series, by J. P. Iddings 326 



Introduction 326 



Absarokite 328 



