REPORT OF THE CHIEF ASTROXOMER 



293 



SESSIONAL PAPER No. 25a 



CONTACT METAMORPHISM. 



The recrystallization of the rocks of the Priest Kiver terrane through the 

 influence of the intruded magma, is most conspicuously shown along the 

 Dewdney trail. This trail threads the floor of the deep Summit creek canyon 

 as it rises from the 2,000-foot level near the Kootenay river to the 3,000-foot 

 level, about nine miles farther up Summit creek. The main contact of the 



2 Miles 



_l 



Vertical and Horizontal 5cale 



Figure 19. Xorth-south section illustrating probable explanation of the great intensity 

 and extent of the contact metamorphisni at Summit Creek. Aureole of 

 contact metamorphism shown by cross-lining. Folds shown in Priest 

 River Terrane purely diagrammatic. 



batholith runs nearly parallel to trail and creek and at an average distance of 

 about 2,200 yards from both. The aureole of contact metamorphism is here 

 two to three miles wide. The metamorphic effects seen along the trail are, 

 however, greater than they would be at the same distance from the exposed 

 igneous contact and on the same level as the nearest contact. The line of 

 contact runs generally from 2,000 to 3,200 feet higher than the trail at the 

 bottom of the canyon. The extraordinary intensity of the metamorphism 

 along the trail is, thus, in part explained by the depth to which Summit creek 

 has excavated its canyon in the sloping roof of the batholith. In other words, 

 the strength of the metamorphism suggests that the contact-surface of the 

 batholith is not vertical but dips under the creek bed; and that, on this south- 

 ern extremity at least, the batholith has the section of a body enlarging down- 

 wardly. (Figure 19.) 



