GEOLOGICAL RELATIONS 361 



trusive tongues cutting the schist pendant north of Horseshoe mountain, 

 as illustrated in figure 4. The contacts between the two batholiths are of 

 knife-edge sharpness. The younger granite, persisting in all essential 

 characters even to the main contacts, sends powerful apophyses into the 

 older granite, exactly as if the two batholiths were in age several geological 

 periods apart. Both are of Tertiary age and bear witness to the tremen- 

 dous plutonic energies set free in a late epoch of Cordilleran history. 

 Quietly, but with steady, incalculable force, this youngest magma worked 

 its way upward and replaced the invaded rocks. During the same time 

 the satellitic Park granite was irrupted with the stock form and relations. 

 Smith and Mendenhall have described a large batholith of "quartz 

 monzonite or quartz diorite" (granodiorite?) intrusive into Miocene ar- 

 gillites at Snoqualmie pass in the northern Cascades and 100 miles south- 

 west of Osoyoos lake.* This is one of the youngest batholiths yet de- 

 scribed in the world. The more basic phases of. the Similkameen batho- 

 lith present similarities to the rock at Snoqualmie pass. It is thus pos- 

 sible that the Similkameen granite was irrupted in late Miocene or even 

 in Pliocene time ; the Cathedral batholith is yet more recent. 



Besume of the Geological History 



The stages in the penological development of the Okanagan Composite 

 batholith as it now exists may now be summarized. We begin with the 

 oldest stage that is of importance in this particular history : 



1. Intense metamorphism of Paleozoic and earlier formations (prob- 

 ably) in the late Carboniferous period, accompanied or soon followed by 

 the intrusion of the Chopaka, Ashnola, and Basic Complex gabbros and 

 peridotites in chonolithic (?) or other relations. Differentiation within 

 these bodies. 



2. In Jurassic time, batholithic irruption of the Osoyoos and Eemmel 

 granodiorites. Contact differentiation of quartz diorite in the former, at 

 least. 



3. Rapid denudation of the granodiorite batholiths in the late Jurassic ; 

 local subsidence of their eroded surface beneath the sea, there to be cov- 

 ered with a thick blanket of Cretaceous sediments which are in part com- 

 posed of debris from the granodiorite itself. 



4. At the close of the Laramie period, revolutionary orogenic disturb- 

 ance, shearing and crushing the granodiorites and basic intrusives. In 

 the former, development of strong crush-foliation and banding with the 



*Bull. Geol. Soc. Am., vol. 11, 1900, p. 223. 



XXXIII — Bull. Geol. Soc. Am.. Vol. 17, 1905 



