REPORT OF TEE CEIEF ASTRONOMER 501 



SESSIONAL PAPER No. 25a 



Either to north or to south of the Boundary belt the field-conditions may favour 

 the discovery of the essential geological features of the series; within the belt 

 they are distinctly unfavourable and the writer's results are largely negative. 



The Hozomeen ridge is composed of a group of massive greenstones, cherty 

 quartzites, and rare intercalations of white to pale gray limestone. Of these the 

 greenstone is dominant wherever outcrops occur, and appears to make up the 

 nearly or quite inaccessible horn of Mt. Hozomeen as well as the higher though 

 accessible summit just to the north. The greenstone has everywhere been 

 crushed and altered, in both respects so profoundly that the writer was unable to 

 secure a single specimen which in character even approached the original 

 material. Minute jointing is extraordinarily developed, making it almost 

 impossible to trim a specimen to standard size or shape; usually the very 

 freshest rock crumbled to small polygonal pieces under the hammer. 



The rock has the normal dark gray-green colour and almost aphanitic, 

 massive character of greenstone. Occasionally it shows a brecciated structure 

 which simulates that of a pyroclastic, yet no distinct beds of agglomerate oi 

 tuff could be discerned. Everywhere irregular, discontinuous and innumerable 

 planes of fracture, generally heavily sliekened, cut the rock in all directions. At 

 one or two points suggestions of an original vesicular structure were 

 encountered but they were too obscure to make the effusive origin of the green- 

 stone perfectly clear. Nevertheless, the writer believes that this rock does 

 represent the altered equivalent of basaltic or basic-andesite flows of great 

 aggregate thickness. 



Four typical specimens were examined under the microscope. They were 

 all found to be essentially made up of secondary material, — the usual mat of 

 uralite or actinolitic hornblende, epidote, chlorite, saussurite, omphacite, caleite, 

 zoisite, and quartz, with here and there a granulated, altered plagioclase feldspar. 

 Original crystal forms have been obliterated in all four thin sections. 



If all of the greenstone exposed in the Hozomeen ridge is of extrusive 

 origin, its total thickness must be great; 2,000 feet is a safe minimum. 



The cherty quartzite is the next most important member of the series. If 

 its whole strength were known it might prove to have a greater thickness than 

 the greenstone. Some colour is lent to this idea by the discovery of other thick 

 sections of the quartzite as it is followed along the Skagit valley trail towards 

 Hope. In that stretch a large quantity of phyllite was found to be interbedded 

 with the quartzite. In the Boundary sections phyllitic phases were comparatively 

 rare; the silicious sediments there are pretty generally gray to greenish gray, 

 compact, cherty rocks. They are thin to thick -bedded, breaking often with 

 subconchoidal fracture. Like the greenstones they are heavily jointed, crushed 

 and veinleted with white quartz. Under the microscope the rock is seen to 

 have the common cryptocrystalline to microcrystalline structure of chert in 

 which minute grains of apparently clastic quartz are embedded. 



The limestone beds intercalated in the greenstone were observed only on 

 the long spur running north-northeast from Mt. Hozomeen. Wherever seen, the 

 beds are never continuous for more than a few hundred feet but occur as pods or 



