SUMMARY 375 



d. Crystallization of the mass during a viscous condition approaching 

 that of a solid solution.* 



General Summary 



1. At the 49th parallel of latitude the Okanagan mountains and a part 

 of the belt of the Interior plateaus (the Interior plateau of Dawson) have 

 been carved by erosion out of an assemblage of plutonic igneous rocks 

 which, in spite of the diverse lithological character of the rocks, should be 

 regarded as an enormous single member of the Cordilleran structure. 

 This plutonic group is named the Okanagan Composite batholith. The 

 details of its constitution are given in a foregoing resume of its geological 

 history. 



2. This composite batholith was of slow development, beginning with 

 small intrusions in late Paleozoic (or possibly Triassic) time, increased 

 by great batholithic irruptions of granodiorite during the Jurassic, and 

 completed by likewise immense irruptions of alkaline hornblende-biotite 

 granite and biotite granite — batholiths of Tertiary age, possibly as late as 

 the Upper Miocene or the Pliocene. The satellitic Tertiary stock of 

 Castle peak in the Hozomeen range, is composed of normal granodiorite. 



3. The local intrusion of a small, composite body of malignites and 

 nepheline syenites; the regular basification along the batholith and stock 

 contacts, giving collars of monzonites and diorites ; and the sporadic ap- 

 pearance of certain peridotites (hornblendites and dunites) are probably 

 all incidents of magmatic differentiation and do not directly represent 

 the compositions of general subcrustal magmas. 



4. The composite batholith and the Castle Peak stock offer striking 

 testimony to the probable truth of the assimilation-differentiation theory 

 of granitic rocks. A very brief summary of this theor}' is given above in 

 the form of a skeleton kej to the history of a batholithic magma. 



5. The composite batholith includes two consanguineous series of in- 

 trusions. The older one is non-alkaline; the younger, alkaline. They 

 are separated in time by the whole Cretaceous period, at least. 



6. The two consanguineous series nevertheless appear to belong to one 

 petrogenic cycle. Throughout the cycle batholithic intrusion has fol- 

 lowed the usual law of decrease in magmatic density and increase of mag- 

 matic acidity with the progress of time. 



7. Exposures of contact surfaces in the Castle Peak stock and in the 

 Similkameen batholith illustrate with remarkable clearness the downward 

 enlargement of such bodies with depth. 



*Cf. Brauns, Chemische Mineralogie. Leipzig, 1890, p. 97. 



