Frof. Bonney — Rock-specimens from the Canadian Rockies. 515 



a nearly white, fairly crystalline limestone, which under the micro- 

 scope proves to be composed of calcite grains (slightly dolomitic 

 and banded), varying in diameter from about -0014 to -025 inch, 

 with a slight brown, feebly pleochroic stain in one or two places, 

 and a few very dark brown specks (? iron-oxide). The fragment 

 from the summit of Pope's Col [2016] is a darkish-grey sub- 

 crystalline limestone, weathering to a paler tint, crossed by a thin 

 vein of calcite which slightly projects on a weather-worn surface. 

 Microscopic examination shows it to be a dolomitic limestone com- 

 posed (except for a slight staining near a vein) of grains fairly 

 uniform in size and often about -005 or -006 inch in diameter. The 

 summit of Mount St. Piran [2019] is a rather slabby and banded 

 quartzite of a brownish or purplish grey colour, obviously containing, 

 especially in one band, an iron-oxide which weathers away in brown 

 specks. The microscope shows it to be mainly composed of quartz 

 grains in finer and coarser bands, the former being mostly subangular 

 and often rather less than -001 inch in diameter. A few grains, 

 however, are a brownish grey colour, and exhibit, with crossed 

 nicols, a minute aggregate structure, possibly resulting from the 

 alteration of felspar ; these are from "025 to -035 inch in diameter, 

 and usually well rounded. One or two streaky aggregates of 

 chlorite are present, and this mineral can be detected, though 

 seldom, in the last-named grains. There may be a little minute 

 rutile. The quartz cementing the larger grains of the same mineral 

 is in optical continuity with that to which it adheres, though the 

 outline of this is often defined by a line of iron-oxide. Obviously 

 most of the latter was deposited almost simultaneously with the 

 cementing silica. The rock from the summit of Mitre Col [2018] 

 is a rudely prismatic (jointed) fragment of a darkish subcrystalline 

 limestone, with small white spots rather irregular in shape and size. 

 A slice cut parallel with the probable direction of bedding shows 

 a general similarity to that from Pope's Col, except that here and 

 there patches occur composed of grains nearly treble the ordinary 

 diameter, but with no recognizable sign of organic structure. A few 

 dark-brown specks are probably iron-oxide. The summit rock of 

 Mitre Peak [2020] is a rather crystalline, nearly white limestone, 

 somewhat mottled by dull and darkish lead-coloured spots, which 

 is rudely defined by joint and bedding planes. A slice cut per- 

 pendicular to the latter shows it to be a crystalline limestone, almost 

 without sign of dolomitization. Grains about -015 inch in diameter 

 occur in patches, the rest being about half that width. Some small 

 grains and specks of iron-oxide are present. 



The next group of specimens come from the neighbourhood of 

 Mount Ball, which rises on the divide a little to the south of 

 Vermillion Pass and about 26 miles S.S.E. of Hector Pass. Of these 

 [2010], [2012], and [2014] come from a valley on the east side of 

 the divide which leads from the north to Mount Ball. The first, 

 labelled " from the great boulder," is a pale-grey subcrystalline 

 limestone, with minute crystals sparkling iu a compact matrix, like 

 that of some of the purest British Carboniferous limestones. The 



DECADE IV. VOL. IX. NO. XII. 3o 



