AND GEOLOGY OF THE COLUMBIA. 105 



Microscopic. — Clastic looking fragments of quartz form a large part of the rock, and 

 mixed with or folded about them is a pale green mica-like mineral, probably the variety of 

 muscovite called sericite, or possibly chlorite. Irregular masses of brown biotite, garnet, 

 magnetite, and small quantities of titanite, may be looked on as accessory minerals. 



In addition to the minerals des'-ribed, one bluish grey specimen contains a consider- 

 able amount of plagioclase, long crystals of hornblende (greenish blue and yellow 

 dichroism) bordered with biotite, and slender colorless prisms, with a rovigh basal 

 cleavage and parallel extinction, perhaps sillimanite. 



Schistose Conglomerates. — Macroscopic. — A few greenish schistose rocks are filled 

 with small round or angular fragments or pebbles of quartz and felspar. They remind 

 one of a rock described from Beaver. 



Microscojiic. — The quartz is of the kind usual in granites ; the felspar sometimes shows 

 the plagioclase structure, but often appears to be orthoclase, though too badly weathered 

 to be unmistakably so. The enclosing layers consist of green and brown biotite, mus- 

 covite (sericite) and blue green chlorite, with many grains of magnetite. The autogenous 

 minerals are much more highly individualized than in similar rock from Beaver. 



(4.) Surprise Mountain. 



Mica Schist. — Macroscopic. — The medium-grained, brownish-grey mica schist from 

 the summit of Surprise Mountain, differs much in habitus from the fine grained sericitic 

 schist from the rapids at its base. Unlike the latter, it shows little or no evidence of a 

 clastic origin of any of its constituents. 



Slicroscopic. — The rock contains large quantities of quartz, primary in appearance, 

 with cavities showing libellules in motion, probably a little felspar, and much brown 

 biotite with optic axes rather wide apart. There is also a considerable amount of musco- 

 vite in well defined individuals very unlike the confused, wavy masses found in the 

 Surprise Rapids schists. There are some yellowish and greyish decomposition products, 

 much magnetite and a few garnets. 



HoRNBLENDic ScHiST. — Macroscopic. — Interstratified with the mica schist is found a 

 fine grained, dark grey, almost black, hornblendic schist. 



Microscopic. — It proves lander the microscope to be thoroughly crystalline and 

 autogenous in look ; and consists chiefly of quartz in small, clear individuals, and green 

 hornblende showing no crystalline forms, but clean edged and of a primary appearance. 

 A little biotite and many sharply-outlined black grains, probably of magnetite, are 

 also found. 



(5.) Lalie Timbaskis Region {Rocky Mountain side of the Columbia) 



Quartzites. — Macroscopic. — These rocks occur near the Timbaskis schists, but are 

 very distinct in habitus. They are white, yellowish white or light grey, always show a 

 few scales of mica on cleavage surfaces, and sometimes enough mica to form a transition 

 toward mica schist. 



Sec. IV, 1889. U. 



