166 DEPARTMENT OF TEE INTERIOR 



2 GEORGE V., A. 1912 



SYSTEMATIC VARIATION IN ROCK-CHARACTER OF THE GEOSYNCLINAL AT THE FORTY- 

 NINTH PARALLEL. 



A study of the correlation plate (Plate 20) and the foregoing descrip- 

 tions show that all four of the sedimentary series fit into a single scheme 

 of rock-genesis. Distance from the ancient shore-line, off which the many beds 

 were deposited, is the main key to the scheme. It is about 120 miles from the 

 thick monoclinal section of the Summit series in the Selkirks to the spectacular 

 monoclinal section of the Lewis series on Oil creek in the Clarke range. The 

 east and west line joining the two monoclines is not only transverse to the 

 existing mountain ranges but is also the line of cross-section through what 

 •seems to be the thickest part of the great stratified prism. In the western mono- 

 cline the sediments are largely littoral deposits, — coarse and fine conglomerates, 

 coarse grits and coarse and fine sandstones. In the eastern monocline the sedi- 

 ments are those characteristic not so much of very deep water as of mere 

 distance from the immediate shore-line, the home of turbulent waves, strong 

 wave-erosion, and powerful transportation of coarse detritus. The members 

 of the Galton and Purcell series represent the expected transitional formations 

 between the two extremes. 



In general the prism is lithologically homogeneous in its middle part and 

 highly heterogeneous in the zone of shore-deposits, and also highly hetero- 

 geneous in the eastern end of the section, far from the old shore-line. 



An estimate has been made of the relative proportions of conglomerate, 

 grit, sandstone, argillite (metargillite), and limestones occurring in each 

 member of the four series. The results of the estimate have been tabulated as 

 follows : — 



