156 



accompanied by some contemporaneous volcanic action. 

 Surface lavas of both central-eruption type and fissure- 

 eruption type are found in the Pennsylvanian, Triassic, 

 Eocene, and Oligocene downwarps of the Western Belt. 

 In our section the volcanics of the Triassic and Tertiary 

 are much thicker than the sediments of their respective 

 dates. The Western Belt is, in fact, a volcanic province of 

 the first order, whether considered as to volume of extra- 

 vasated material, as to persistence of eruptivity in geolo- 

 gical time, or as to area of country still covered by the 

 lavas. The great cone of Mt. Baker, south of the railway 

 at Mission Junction, represents Pleistocene-Recent 

 vulcanism. 



Batholithic intrusions are very rare in the Eastern Belt and 

 are entirely absent in the railway section. They cut the 

 Paleozoic strata of the Western Belt on a scale unmatched 

 elsewhere in the world except, perhaps, in the Pre-Cambrian 

 terrane of Eastern Canada, Fennoscandia, etc. The com- 

 posite Coast Range batholith of British Columbia and Alas- 

 ka is about 1200 miles (1930 km.) in length, with an average 

 width of nearly 90 miles (144 km.). The railway section 

 crosses it in the stretch between Lytton and Vancouver. 

 It is composed of granodiorite and quartz diorite, with 

 diorite, biotite granite, syenite, and allied types. There 

 is clear evidence of successive intrusion but it is agreed 

 that the general date of irruption for the greater part 

 falls in the period from the latest Jurassic to the early 

 Cretaceous. In our section the late Jurassic is the pre- 

 ferred date. Yet it is probable that this batholith, like 

 those in Washington State and in the Kootenay district 

 of British Columbia, received large increment or else batho- 

 lithic replacement in post-Cretaceous time. In the railway 

 section itself such Tertiary batholiths have not yet been 

 proved and the earlier date is generally accepted for many 

 smaller batholiths east of the Fraser river as well as for the 

 Coast Range body. Some of the little sheared granitic 

 masses cutting the western part of the Shuswap terrane are 

 tentatively referred also to the late Jurassic. 



These various bodies illustrate again and again the cross- 

 cutting and apparently bottomless relations of true batho- 

 liths. The main contacts and the attitude of roof-pendants 

 are eloquent in favour of the replacement theory of origin 

 and strongly oppose the "laccolithic" theory. Evidence 

 on this fundamental matter has been collected by: Clapp 



