260 J. Parkinson — The Making of Quartz Schist. 



the origin of the rock is " a matter of conjecture " rather than of 

 proof (p. 209, etc.)- In a quartzite the contrary holds. The clastic 

 origin of the quartzes is obvious, and the form and mode of occurrence 

 of the mica shows it to be detrital ; hence the characters separating 

 normal types of the two groups of rock are clear enough in a thin 

 section, if not in a hand-specimen. 



The rocks which form part of the subject of the present communi- 

 cation were collected from the neighbourhood of the Illecellewaet 

 Glacier in the Selkirk Mountains ; and microscopically present 

 a structure intermediate between that of a quartz schist and that 

 of a quartzite.^ 



Since the gap which separates these two rock types is one which 

 is seldom bridged, I venture to think it may be profitable — (1) 

 to consider the changes which have taken place in the North 

 American rocks which will be referred to as quartz felspar grits ; 

 (2) to compare the latter with some of the older quartzites of 

 India, which present indications of change of a rather different 

 kind ; and (3) to see what help the whole affords in elucidating 

 the difficult problem — the making of a quartz schist. 



1. The Quartz Felspak GtRits.^ 



These form a group of rocks exhibiting slight variations in degree 

 of coarseness and manner of fracture, commonly speckled with 

 obvious grains of felspar and quartz ; although the sheen surfaces, 

 formed through the development of secondary mica, record the 

 pressure which the rock has undergone. In a few localities, e.g. the 

 moraine of the Illecellewaet Glacier, elongated ellipsoidal spots are 

 conspicuous, exhibiting a parallel arrangement, and which average 

 in size 'Sin. x '15 in. X "05 in. As seen in a thin section they consist 

 of very irregular grains of calcite, outlined hj an iron staining, 

 which straggle through the other constituents instead of forming 

 a clearly defined patch. These may possibly be the remains of 

 ■worm burrows distorted by pressure. 



* See also a paper by Professor T. G. Bonney in Quart. Jouru. Geol. Soc, 1888, 

 vol. xliv, p. 32, on the Hiironian Series in the neighbonrhood of Sudbury (Canada) ; 

 a sedimentary series showing changes which approximate them in character to a true- 

 schist. I am greatly indebted to Professor Bonney for opportunity to study his slides 

 of these rocks, and for suggestions given from time to time on this and kindred 

 subjects. 



* The age of these rocks is a matter of interest. The identification is a rather 

 difficult one, and I am indebted to Dr. AVhiteaves and Dr. H. M. Ami, of the 

 Canadian Geological Survey, for kindly replpng to my question on the subject. To 

 the E.N.E. of, and about eighteen miles as the crow flies from, the Illecellewaet 

 Glacier, a Lower Cambrian fauna has been found, and to the westward lies the 

 Shuswap Series, probably of Archrean age. Above the latter and to the east are 

 "dark argillites passing into micaceous schists" (Summary Eep. 1890-1, n.s., v, 

 pt. 1, p. 20a). These are the Nisconlith Series (Lower Cambrian), probably 

 equivalent to the Bow Eiver Series. See also papers by the late Dr. G. M. Dawson, 



'Bull. Geol. Soc. Amer., vol. ii, pp. 165-176, "Note on the Geological Structure 

 of the Selkirk Eange," and Ann. Eep. Geol. Surv. Canada, 1896, vol. vii, pt. B, 

 pp. 28e-34e, in which the quartzites in the vicinity of the Glacier House, Mountain 

 Sir Donald, etc., are placed in the Cambrian system under the name of the Selkirk 

 Series and overlying the Nisconlith Series. 



