REPORT OF THE CHIEF ASTRONOMER 15 



SESSIONAL PAPER No. 25a 



On Simias mountain, coal-bearing, obscurely fossiliferous sandstones and con- 

 glomerates are included in the Huntingdon formation, which is probably equival- 

 ent to the Eocene Puget beds of Washington. A very thick volcanic pile 

 (Oligocene?) occurs on the- eastern slope and is called the Skagit Volcanic 

 formation. 



Rocks assigned to the Hozomeen series are cut by the Custer gneissic bath- 

 olith (sheared granodiorite), outcropping at the summit of the Skagit range. It 

 is possibly of Jurassic age. It is cut by the Tertiary Chilliwack batholith of 

 granodiorite, which is genetically connected with a batholithic mass named the 

 Slesse diorite. Other intrusive masses are also described. The chapter closes 

 with notes on correlation and on the structure of the Skagit range. 



Chapter XIX. — Deals with the correlation of all the bed-rock formations 

 encountered in the Boundary section between the Purcell Trench and the Strait 

 of Georgia, the approximate limits of the Western Geosynclinal Belt at the 

 Boundary line. The correlation of the Forty-ninth Parallel rocks with those 

 described in sections ranging from Alaska to California is then briefly discussed 

 and thrown into tabular form. A summary history of the Western Belt of the 

 Cordillera closes the chapter. 



Chapter XX. — Having described the many formations in the Boundary 

 section, an attempt is here made to summarize the geological history of the 

 Cordillera of the Forty-ninth Parallel. That necessarily brief statement is 

 followed by a note on the theory of mountain-building. 



Chapter XXI. — This chapter gives a sketch of the observations made on 

 the glacial geology of the section. The limits of the great Cordilleran ice-cap 

 at the Forty-ninth Parallel, as to ground-plan and depth, are noted. The two 

 double rows of valley glaciers draining the Rocky Mountains and the Cascade 

 system during the Pleistocene are described. The glaciation of each range is 

 then considered, beginning with the Clarke range on the east. The resume of 

 the chapter is to be found at its closing page. 



Chapter XXII. — Discusses certain of the physiographic problems connect- 

 ed with the section. A note on the origin of the master valleys is followed by 

 a division of the Boundary zone into physiographic provinces, listed in a table. 

 A running account of the morphology of the successive provinces, beginning 

 with the Front range synclinal area, is accompanied by a theoretical discussion 

 of the question as to Tertiary peneplanation of the Front ranges and of the 

 Cascade mountains. The cause for the accordance of summit levels in alpine 

 mountains (large extracts from a preliminary paper on that subject) is con- 

 sidered. The chapter closes with a statement of general conclusions on the 

 physiographic development of the Cordillera of the Forty-ninth Parallel. 



Chapter XXIII. — Is a theoretical chapter dealing primarily with the 

 explanation of the fact that fossils are relatively rare in pre-Ordovician forma- 

 tions, and of the related fact that the great majority of those fossils are not 

 calcareous like most of the post-Cambrian fossil remains. The favoured explana- 



