780 DEPARTMENT OF THE INTERIOR 



2 GEORGE V., A. 1912 



in the Boundary section, as well as the thousands of other igneous bodies which 

 he has studied elsewhere, either in the field or in the literature, gives the theory 

 such cumulative sanction that it has been called a theory rather than a working 

 hypothesis. The writer is emboldened to do this because the whole combination 

 of principles is an eclectic summary of what appear to be the soundest views 

 of petrologists in general. 



Hence, in applying the theory to the Forty-ninth Parallel rocks, only a 

 relatively small part of the proof of its validity is stated. The following para- 

 graphs are thus meant for illustration and review rather than for demonstration. 

 A multitude of field relations remain to be discovered before this, or any other 

 eruptive area can prove the theory. Its exact application to many of the 

 Boundary formations must await the results of future researches. 



Evidence of a Primary Acid Earth-shell. — The postulate of a primary acid 

 shell is supported by the petrographic analysis of the Priest River terrane and 

 of the Rocky Mountain geosynclinal, the one pre-Cambrian entirely, the other 

 partly pre-Cambrian. The Priest River terrane is, on the average, highly sili- 

 cious and it is probable that a minimum thickness of 6,000 feet of pure quartz 

 is represented in the portion exposed within the Boundary belt. It will be 

 remembered that neither bottom nor top of the Priest River series is exposed. 

 The clastic beds of the Rocky Mountain geosynclinal represent from 10,000 

 to 20,000 feet of quartzose material, in which probably 10,000 feet of pure quartz 

 are locally represented. Evidently a pre-Cambrian granitic or gneissic land 

 of great extent must have furnished these sediments. Perhaps the Shuswap 

 feeries of Dawson represents the now exposed equivalent of that ancient terrane. 



The large areas of the pre-Cambrian demonstrated in the Cordillera, in 

 eastern Canada, and elsewhere, are just such terranes, highly batholithic, which 

 would furnish debris like that in the Priest River terrane and the Rocky Moun- 

 tain geosynclinal elastics. Lawson and others have shown that visible pre- 

 Cambrian batholiths were intruded and do not directly represent the original 

 earth's crust, but calculation shows that the material of these batholiths was 

 primary in the sense that it was not derived from quartzless rock through the 

 leaching action of weathering (see page 702). 



We conclude, therefore, that the lands whence the old quartzose sediments 

 of the Boundary section were derived must have been either part of the original 

 granitic crust or, more probably, the more or less remelted and recrystallized 

 equivalent of that crust. The argument is enormously strengthened by the facts 

 which are known concerning the pre-Cambrian sediments of eastern Canada, 

 southern Appalachians, Sweden, Finland, China, Australia, etc. 



Evidence of a Basaltic Substratum. — Among the evidences for the existence 

 of a primary basaltic substratum we have noted: first, the fact that almost all 

 the greater fissure-eruptions of the world are basaltic in composition; secondly, 

 that basalt is the magma most persistently represented in igneous rock provinces ; 

 thirdly, the recurrence of eruptions of basaltic magma from the Keewatin time 

 to the present, and; fourthly, that there is evidence of the direct derivation of 



