MESOZOIC SYSTEMS ALONG THE PACIFIC 



281 



«r— 



Fig. 17.18. Geomorphic divisions of British Columbia and southeastern Alaska showing the divi- 

 sions of the western, or Pacific mountain, belt of the Cordilleran region. To bring the fiord 

 system into prominence the sea within the 100-fathom line is shown in solid black. Within the 



Some stocks or batholiths within the eastern border zone are imper- 

 fectly known. Between the Skeena and Nass rivers the border of the main 

 batholith is irregular with apophyses and outlying stocks of granodiorite. 

 Between Nass River and the Portland Canal, the border is fairly straight. 

 In the Hyder district, a mass of hornblende granodiorite has been called 

 the Texas batholith (Buddington and Chapin, 1929). It is probably ad- 

 jacent to the main Coast Range batholith and is cut by many dikes of 

 younger quartz monzonite and granodiorite. It is locally intensely crushed, 

 evidently from the thrust of the younger intruding magma. Although defi- 

 nitely older than the intrusions that cut it, the Texas batholith is probably 

 post- Jurassic, because it is similar to a nearby quartz diorite at the head of 

 Hastings Arm and Observatory Inlet which is intrusive into the "Bear 

 River series" and Nass argillite of Jurassic age. 



Intrusive bodies are also known in the Atlin and Whitehorse districts, 



black area are many basins which are deeper than 100 fathoms, especially in the fiord 

 channels. After Peacock, 1935. 



but for the most part the vast region northwest of the Hyder district is 

 unknown. 



The great Coast Range batholith itself is inadequately known, but Bud- 

 dington's description (Buddington and Chapin, 1929) for the section 

 between the Portland Canal and the Stikine River is illuminating. The 

 southwest border facies in a belt 5 to 15 miles wide, has the average com- 

 position of a granodiorite, and is composed predominantly of granodiorite, 

 quartz monzonite, and quartz diorite; the eastern border facies, 10 to 15 

 miles wide, is quartz monzonite. Dolmage ( 1923 ) reports that the more 

 silicic variations lie in the center of the batholith south of Portland Canal 

 as Buddington finds to the north, but that there are exceptions. The 

 changes from one type of rock to another appear to take place rather 

 abruptly, but no evidence of brecciation of one variant by another has 

 been seen, except in the small masses of gabbroic and ultrabasic rocks. 



