340 R. A. DALY THE OKANAGAN COMPOSITE BATHOLITH 



the Cordillera elsewhere are wanting in this part of the Cascade system. 

 With thicknesses running into tens of thousands of feet, they once un- 

 questionably composed the Okanagan range, and of them the ancestors of 

 these very boundary mountains were built. Erosion has removed some of 

 the formations, attacking the earth's sedimentary crust from above. There 

 is every reason to believe that perhaps even more of the old mountain sub- 

 stance was removed during the successive batholithic intrusions. Thus 

 the sedimentary crust has also been attacked from beneath; its integrity 

 has been destro} T ed through the displacing or replacing of sediments by 

 igneous magma. In bringing about this gigantic result all the batholiths 

 have acted together. Though they are of very different ages, their ener- 

 gies have been devoted to a common work. Their effects are so integrated 

 that in causing the nearly complete disappearance of the ancient strata 

 they have imitated on a larger scale what occurs with any homogeneous 

 batholith. From this point of view the Boundary belt, stretching from 

 the eastern contact of the Osoyoos batholith to the western contact of the 

 Eemmel batholith, forms a small segment of one composite batholith 

 somewhat broader than the Okanagan range. To emphasize this primary 

 fact, the title of the present paper has been chosen. 



Petrography of the Composite Batholith 

 in general 



Before proceeding to a detailed statement of the structure and history 

 of the composite batholith a brief petrographical description of its com- 

 ponents will be necessary. The chemical study of these rocks has only 

 begun, but, on account of their freshness and coarseness of grain, micro- 

 scopic analysis has been found so trustworthy that the different types can 

 be already sufficiently well classified for the purposes of this discussion of 

 the general geology. Much of the usual petrographical detail has been 

 omitted as not bearing directly on the main problems. 



The rocks will be described as nearly as possible in the order of their 

 respective dates of intrusion. 



CHOPAKA BASIC INTRUSIVES 



The basic and ultra basic intrusives of the Chopaka roof pendant have 

 been described by Smith and Calkins as uralitic gabbro, serpentines, and 

 pyroxenites. Within the area covered by the Commission map (figure 4), 

 the present writer has found no pyroxenite, but has referred all the mas- 

 sive intrusives of the Chopaka pendant (excluding dikes) to two rock 

 types and their metamorphic derivatives. 



