-470 ' DEPARTMENT OF THE INTERIOR 



2 GEORGE V., A. 1912 



granite which answers very well in its description to the Cathedral granite. 



They write: — 



' There is included in this formation [Snoqualmie batholith] . . a 

 mass of more siliceous biotite-granite, which forms Guye Peak, the spur 

 to the west of it. and part of Snoqualmie mountain. Its relation to the 

 granodiorite was not definitely determined, but it is supposed to be derived 

 from the same magma and nearly contemporaneous with it, since grano- 

 diorite and granite show the same relation to the adjacent sediments. . . 

 The biotite-granite, when examined in thin section, is found to contain a 

 large percentage of quartz, about an equal amount of alkali feldspar, some- 

 what less oligoclase, and a little biotite, largely replaced by chlorite. The 

 alkali feldspar is microperthite, in contrast with the orthoclase of the 

 granodiorite, which is usually not notably perthitic. The accessories are 

 magnetite, titanite, zircon, and apatite.'* 



This account of the Snoqualmie batholith suffices to show that there has 

 been a close parallel in the magmatic history of that body and of the compound 

 mass represented by the Sim.ilkameen and Cathedral batholiths. The parallel 

 greatly strengthens the belief that these batholiths at the International Boun- 

 dary are of late Neocene age. 



RESUME OF THE GEOLOGICAL HISTORY. 



The stages in the development of the formations in the belt between Osoyoos 

 lake and the Pasayten river may now be summarized. We begin with the oldest 

 stage which is of importance in this particular history. 



1. Heavy sedimentation during the upper Paleozoic, possibly continued into 

 the Triassic. Contemporaneous vulcanism and injection of dikes, sheets, and 

 larger chonolithic (?) masses of gabbro and peridotitic magmas, the intrusives 

 perhaps dating from the close of this period. The sedimentation and vulcanism 

 produced the rocks of the Anarchist series, tentatively regarded as mostly of 

 Carboniferous age. The intrusive bodies are represented in the Chopaka, Ash- 

 nola, Basic Complex, and Eichter mountain gabbros and ultra-basic rocks. 

 Pome differentiation within the intrusive masses. 



2. In Mesozoic time, probably during the Jurassic, intense deformation and 

 metamorphism of most of the rocks so far mentioned. Strong mountain- 

 building. 



3. During the somewhat later Jurassic, batholithic irruption of the Osoyoos 

 iind Remmel granodiorites. Contact diffei*entiation of quartz diorite in the 

 former, at least. 



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

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

 with a thick blanket of Cretaceous sediments which are in part composed of 

 debris from the granodiorite itself. 



* Snoqualmie Folio, page 9. 



