REPORT OF THE CHIEF ASTRONOMER 265 



SESSIONAL PAPER No. 25a 



At Summit creek and north of it, the rocks of the helt have been pro- 

 foundly metamorphosed by the Bayonne granodiorite intrusion. The effects 

 are most notable in the schistose bands. In them the small shreds and foils 

 of sericite, chlorite and biotite are replaced by felted aggregates of large biotite 

 and muscovite foils. The resulting coarse-grained mica schist bears a most 

 striking contrast to the more phyllitic schists far from the batholithic contact. 

 Though the recrystallization by contact-action is so pronounced, the original 

 banding or bedding is as fully marked as in the staple phases of these old 

 sedimentaries. The thin bands of coarse schist are sharply marked off from 

 the enclosing quartzite, which, though it bears disseminated plates of biotite 

 and muscovite of relatively large size, is still a true hard quartzite. Occasion- 

 ally minute, deeply coloured tourmalines are seen under the microscope to be 

 distributed through the quartzose matrix. Feldspars are characteristically 

 absent, or at least, are indeterminable in the normal schist and quartzite, but 

 both plagioclase and orthoclase are recognizable in considerable amounts in 

 the schists and quartzites of the thermally metamorphosed part of the belt. It 

 is not possible to attribute their presence with certainty to feldspathization 

 by the granitic magma, however probable it may seem from the field relations 

 cf the feldspar-bearing phase. 



Strong co nt act-met amorphism is visible for at least two miles from the 

 granite contact. The great width of the metamorphic collar as illustrated in 

 belts D, E and G indicate the probability that the contact-surface of the granite 

 body plunges under the rocks at and south of Summit creek. The vertical dis- 

 tance between the granite and the rocks exposed in the depths of the canyon 

 at the creek is probably less than two miles. (See Figure 19.) 



The best exposures of the belt were found on the ridge running southeast 

 from North Star mountain. There the strike of the bedding, the planes of 

 which usually coincide with the schistosity planes, varied from 1ST. 25° W. to 

 2s. — and — S., the dip varies from 75° E. to 70° W., with the average about 85° 

 E. The nearly vertical dip and meridional strike persist for a distance of some 

 six miles north of the Boundary line; but along Summit creek the strike has 

 swung around, so as to run, on the average, about N. 40° E. near belt and 

 gradually approaching N. 65° E. as the eastern limit of quartzites on the 

 Dewdney trail is approached. Throughout the whole width of the belt on the 

 Dewdney trail, the strike thus follows very closely the general contact-line of 

 the Bayonne granite; the relation affords an excellent illustration of the 

 development of peripheral cleavage about a batholith. The dip of the banding 

 (bedding) in the schist-quartzite along this contact collar seems to coincide 

 generally with the "dip of the schistosity. It averages about 60° to the north- 

 west, but is highly variable, as expected in a belt of rocks energetically dis- 

 placed and mashed during batholithic intrusion. 



Petrography of Belt E. — Belt E . is composed of a group of acid sediments 

 even more intensely metamorphosed than those of belt D. The dominant type 

 is a highly sericitic schist in which large biotite foils have been extensively 



