MESOZOIC SYSTEMS ALONG THE PACIFIC 



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Fig. 17.21. Sculpture pattern of the coastland of British Columbia and southeastern Alaska 

 (obtained by drawing straight lines along all nearly straight fiord reaches, lake shores, stream 

 courses, and portions of coastline. The complex pattern resolves itself into a concordant pattern 



consisting of lines running parallel and at right angles to the curving longitudinal grain, and 

 a discordant pattern composed of lines lying north-south and east-west obliquely to the grain. 

 All four directions are prominent directions of jointing. After Peacock, 1935. 



Age of the Batholiths. The following summary of the age of the great 

 -batholiths is taken from Buddington and Chapin (1929). 



The age of the Mesozoic intrusive rocks has not been definitely determined. 

 To the northeast, on the east side of the batholith in the Whitehorse district, 

 {Yukon Territory, the intrusive rocks are reported by Cockfield to cut rocks of 

 (Middle Jurassic age and, therefore, to be probably of Upper Jurassic age or 

 jlater. Hanson reports that on the east side of the batholith, in British Columbia, 

 between Skeena River and Steward, the Coast Range batholith intrudes the 

 Hazelton group (Jurassic) but does not intrude the Skeena (Lower Cretaceous) 

 Iseries. He says: "It is, therefore, probably mainly of Upper Jurassic age, but 

 parts of the batholith may be of later age." Dolmage, in describing the Tatla- 

 BeUa Coola area, writes: "In Taseko Lake district, what appears to be the main 

 Coast Range batholith cuts a thick series of coarse fragmental volcanic rocks in 

 iwhich the writer found plant remains, determined by E. W. Berry to be of 

 'Cretaceous age. . . . This evidence proves that this part at least of the batho- 

 lith is younger than the lowest Cretaceous, and the evidence found in Tadavoko 

 Lake, Taseko Lake, and Bridge River districts strongly suggests that much of 

 the eastern part of the batholith is of post-basal Lower Cretaceous." Cairnes 



suggests that at the southeastern part of the batholith, on the eastern border, 

 there are intrusions of two ages. Masses of intrusive rocks that cut probable 

 Jurassic beds are reported by him to be overlain unconformably by beds of 

 Lower Cretaceous age, and the Lower Cretaceous beds are in turn cut by in- 

 trusions of pre-Tertiary age. On Vancouver Island the Mesozoic intrusive rocks 

 are known definitely to be older than Upper Cretaceous. 



In southeastern Alaska all the intrusive rocks classed as Mesozoic are defi- 

 nitely known to be older than the Eocene. On Chicagof Island intrusions of the 

 Coast Range type are proved by Overbeck to cut fossiliferous beds ol Upper 

 Jurassic age. The writer is convinced that on Admiralty Island intrusions of the 

 Coast Range type cut beds which, where not metamorphosed, carry the fossil 

 Aucella crassicollis and which are therefore probablv of Lower Cretaceous age. 

 At the head of Portland Canal there is positive evidence of two epochs of in- 

 trusion; the older batholith cuts beds of the Hazelton series (Jurassic) and is in 

 turn intruded by the quartz monzonite of the Coast Range batholith. 



It is evident that for the most part the youngest beds with which the Meso- 

 zoic intrusive rocks are found in contact are of Middle or Upper Jurassic age; 

 at a number of localities intrusive rocks of the Coast Range tvpe cut Lower 

 Cretaceous formations; there were at least two epochs of intrusion; and the 

 Mesozoic intrusive rocks are all older than the Upper Cretaceous. So far as 



