REPORT OF TEE CEIEF ASTRONOMER 433 



SESSIONAL PAPER No. 25a 



Tertiary (?) Eocks at Osoyoos Lake. 



In passing, it may be noted that a coarse conglomerate unconformably over- 

 lying the Anarchist series of Kruger mountain was found on the western side 

 of Osoyoos lake at a point about two miles south of the Boundary line. The 

 rounded, angular or subangular pebbles are often large and bouldery. They 

 consist chiefly of granite, gneissic granite, and quartz or quartzite. The cement 

 is feldspathic and arkose-like. This formation has been briefly described by 

 Messrs. Smith and Calkins, who regard it as probably of Tertiary age.* The 

 relations are much like those of the Kettle Biver beds (Oligocene). This deposit 

 does not continue as far as the Boundary line and accordingly is not mapped in 

 the sheet. The bedding of the conglomerate is obscure but the probable 

 dip is about 70° in a northerly direction; the mass has been notably deformed. 



PETROOBAPHY OF THE COMPOSITE BATHOUTH. 



Before proceeding to a detailed statement of the structure and history of 

 the composite batholith a brief petrographical description of its components will 

 be necessary. Much of the usual petrographical detail has been omitted as not 

 bearing directly on the main problems. 



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

 their respective dates of intrusion. 



. Bichter Mountain Hornblendite. 



The Anarchist series of greenstones is cut by at least one large body of an 

 ultra-basic, greenish-black (when fresh), coarse-grained rock which outcrops 

 freely on the slopes of Bichter mountain northwest of the Bichter ranch. The 

 microscope shows that this rock is composed of dark green hornblende (appar- 

 ently primary) and a diopsidic pyroxene which is nearly colourless in thin 

 section; the former mineral is generally in excess. Apatite, much titaniferous 

 magnetite, and some titanite are the accessories. No feldspar could be detected. 

 Uralite or uralitic, pale-coloured amphibole, quartz, zoisite, epidote, and chlorite 

 are secondary products. The pyroxene does not show the diallagic parting. The 

 rock may be classified as a pyroxene-rich hornblendite. The specific gravity of 

 the freshest of three specimens is 3-302. This rock body has been crushed and 

 its minerals are generally considerably altered. Its boundaries have not been 

 so clearly determined that it could be advisedly mapped. The best exposures 

 have, in fact, been found just north of the five-mile belt limit, on the top of the 

 mountain. The body seems to cover more than the half of a square mile at 

 least. 



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. 



* G. 0. Smith and F. C. Calkins, Bull. 235, U.S. Geol. Surv., 1904, p. 33. 



25a— vol. ii— 28 



