DEPARTMENT OF THE INTERIOR 



2 GEORGE V, A. 1912 



Page. 



Eastern Geosynclinal Belt of the Cordillera 195 



Axis of the Rocky Mountain geosynclinal 196 



Upper Paleozoic portion of the Rocky Mountain geosynclinal 203 



CHAPTER IX. 



Purcell Lava and associated intrusives 207 



Introduction 207 



Purcell Lava of the McGillivray range 207 



Dikes and sills in the McGillivray range 212 



Purcell Lava in the Galton range 212 



Purcell Lava in the Clarke range 213 



Dikes and sills in the Clarke range 214 



Purcell Lava and associated intrusives in the Lewis range 216 



Relation of sills and dikes to the Purcell extrusive 218 



Summary 219 



CHAPTER X. 



Intrusive sills of the Purcell mountain system 221 



Introduction 221 



Usual composition of the intrusives 222 



Variations from the usual composition 225 



Moyie sills 226 



Abnormal biotite granite 228 



Abnormal hornblende-biotite granite 232 



Intermediate rock-type 232 



Abnormal hornblende gabbro 233 



Resume of the petrography 235 



Essential features of the different sills 236 



Origin of the acid phases 238 



Preferred explanation 238 



Plat position of quartzite at time of intrusion 239 



Superfusion of sill magma 240 



Chemical comparison of granite and intruded sediments. . . . 240 



Comparison with other sills in the Purcell range 243 



Evidence of xenoliths 243 



Hybrid rock 244 



Assimilation at deeper levels 246 



Assimilation through magmatic vapours 247 



Summary of the arguments for assimilation 247 



Gravitative differentiation 247 



Similar and analogous cases 249 



General conclusion and application 252 



