REPORT OF TEE CHIEF ASTRONOMER' 295 



SESSIONAL PAPER No. 25a 



The study of several thin sections has convinced the writer that the amphi- 

 bole has been generated at the expense of the dolomitic grains disseminated 

 through the cement, thus illustrating a familiar phase of the metamorphism of 

 carbonate-bearing rocks. When the carbonate was abundant in the cement, the 

 actinolite now forms as much as a third or a half of the rock. Considerable 

 epidote and basic plagioclase were also formed in some beds. Such metamorphic 

 effects are noteworthy in view of the distance of these outcrops from the main 

 batholithic contact, — about 3,000 yards. A partial explanation of the metamor- 

 phic intensity is again to be found in the probable fact that the granodiorite 

 lies beneath these outcrops and at a distance of considerably less than 3,000 

 yards downward. 



Two specimens of the Irene lavas were collected at the Dewdney trail. 

 These seem to be typical of the lavas of the exomorphic zone where, as a rule, 

 they have been completely changed to fine-grained or medium-grained, highly 

 fissile hornblende schists. Green hornblende and quartz are the principal com- 

 ponents; grains of carbonate, apparently dolomite, and a little basic plagio- 

 clase are present in both thin sections. 



The phyllitic schists of the Monk formation have been signally metamor- 

 phosed by the batholithic intrusion. For a distance of a half mile or more 

 outward from the granite, these rocks have been converted into a schistose 

 hornfels composed of quartz, muscovite, biotite, sillimanite, and red garnet, 

 along with much untwinned feldspar, apparently all orthoclase. The muscovite 

 foils either lie in the plane of sohistosity or occur with random orientations 

 through the rock. In the latter case they are spangles measuring from 0-5 

 mm. to 1-5 mm. in diameter and are in phenocrystic relation to other consti- 

 tuents. The sillimanite has the usual development in needles which are often 

 aggregated in tufts or sheaves very conspicuous under the microscope. The 

 orthoclase grains show a tendency to aggregate along with some grains of 

 quartz in lenses 1 mm. to 2 mm. long, these lenses lying in the plane of 

 sohistosity. The abundance of the orthoclase in some of the specimens suggests 

 that its substance has been introduced from the magma, but this is not certain. 

 The garnet is pale reddish to nearly colourless in thin section and has the usual 

 habit of the mineral in contact-zones. 



On the top of the 6,600-foot ridge which overlooks Summit creek on the 

 north and runs eastward directly from the peaks at the western head of the 

 creek, a thick series of ferruginous schists are exposed for a distance of a mile 

 measured along the ridge. These schists dip under the Wolf grit and overlie 

 the 200-foot bed of breccia-conglomerate at the top of the Irene volcanic forma- 

 tion. There is little doubt that these ferruginous schists are the much meta- 

 morphosed equivalents of the rocks of the Monk formation. Four type speci- 

 mens were collected at points abotit 1-5 miles from the contact of the Bayonne 

 granite. All of them have been microscopically examined and prove to belong 

 to the one species of staurolite-schist. The staurolites form subidiomorphic 

 crystals and anhedra of all sizes up to 15 mm. in length. In transmitted light 

 they are usually of a strong yellow colour. As usual, quartz inclusions are 



