REPORT OF TEE CHIEF ASTRONOMER 467 



SESSIONAL PAPER No. 25a 



still preserved even in the medium grained facies of the gabbro. In a bathc- 

 lithic rock of that texture, fluidal arrangement of the minerals is very rare. 

 The infinitely diverse composition and structure of the Basic Complex much 

 more clearly points to a non-bath olithic origin. One imagines rather that the 

 lithological and structural complications are in this case such as might appear 

 at the deep-seated focus of an ancient volcanic area. The geological record has, 

 however, been too largely obscured or destroyed that any of these hypotheses 

 concerning the basic intrusives can be verified. 



One fact is certain, that all of the bodies are older than the granites by 

 which they are surrounded. Their contacts with the granites are the sharpest 

 possible; gabbro or peridotite is pierced by many typical apophyses of granite 

 or granodiorite which has often shattered the basic rocks and isolated blocks 

 which now lie within the basic body. Here there is no question of the gabbros 

 being differentiation products from their respective granitic magmas, as so often 

 described in the granodiorite batholiths of California.* There remains, secondly., 

 the conclusion that these basic intrusives were probably not of batholithic size. 

 They show that some time before the real development of the Okanagan com- 

 posite batholith began, a basic, subcrustal magma was erupted on a limited 

 scale— possibly in the form of stocks, possibly in the form of chonoliths. 



Undoubted batholithic intrusion began with the irruption of the grano- 

 diorites. The familiar phenomena of such intrusion are exhibited along the 

 contacts of the Osoyoos batholith. For several hundred yards from the igneous 

 body the phyllites have been converted into typical, often garnetiferous, mica 

 schists. This collar of thermal or hydrothermal metamorphism would doubtless 

 be yet more conspicuous if at the time of intrusion the Paleozoic series had not 

 already been partly recry stall ized in the earlier dynamic metamorphism of the 

 region. 



The Bemmel batholith is, as we have seen, composed of granodiorite similar 

 in original composition to the rock of the Osoyoos batholith. Fossiliferous 

 Lower Cretaceous arkose sandstones, grits, and conglomerates overlie the 

 Rernmel unconformably. The materials for these rocks were in part derived 

 from the secular weathering of the Eemmel granodiorite, the weathering being 

 accompanied by rapid deposition of the debris in a local sea of transgression. 

 Arkose sandstones, which alone measure more than 10,000 feet in thickness, 

 were thus deposited in a down-warped marine area just west of the Pasayten 

 river. To furnish such a volume of sediment, there would appear to have been 

 in the region, preferably to the eastward of the Pasayten, a much larger area of 

 granitic rocks than is now represented in the Eemmel and Osoyoos batholiths 

 combined. It is possible, indeed, that at that time these two batholiths were 

 part of one huge mass of granodiorite which largely occupied the site of what is 

 now the Okanagan composite batholith. Both Bemmel and Osoyoos grano- 

 diorites have suffered profound metamorphism, so similar in its effects in the 

 two rock masses that it may most simply be attributed to the same period of 

 orogenic disturbance. The systematic parallelism of the shear zones in each 



* See many of the Californian folios issued by the U.S. Geological Survey. 

 25a— vol. ii— 30* 



