MESOZOIC SYSTEMS ALONG THE PACIFIC 



289 



T2 



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J2 



T3 



10 

 -l MILES 



Fig. 17.23. Cross sections of the east coast of the southern part of Graham Island of the 

 Queen Charlotte Islands, British Columbia. After MacKenzie, 1916. Jl, Maude fm. (banded 

 argillites and tuffs. Lower Jurassic or Triassic ?); J2, Yakoun fm. (basal agglomerates and minor 

 flows. Middle Jurassic); K2, Kano quartz diorite; Kl, Haida fm. (sandstone, shale, and coal. 



obstructed by the relatively much greater impermeability across the foliated 

 surfaces and that portion highly metamorphosed above and adjacent to the 

 batholith must lie below the present topographic surface, deeper down on its 

 flank. 



The gneissic structure of the batholith suggests that the magma moved up- 

 ward along planes dipping steeply to the northeast and that the maximum 

 effect of its thrust was directed against the adjoining formations on the south- 

 west. The country rock was probably irregularly domed up to a considerable 

 extent by the invading magma, was fractured, faulted, and stoped to some ex- 

 tent, and was thrust aside to a very considerable degree. There is abundant 

 evidence in residual structures and in the composition of the resulting rocks 

 J that, locally, narrow belts of sediment were wholly incorporated in the magma 

 through a process of reactive replacement, but this was probably not the major 

 factor in the process of emplacement of the batholith. 



Upper Cretaceous); K2, Honna fm. (conglomerate and sanastone. Upper Cretaceous); K3, 

 Skidegate fm. (sandstone and shale. Upper Cretaceous); T2, Skonun fm. (sandstone, shale, and 

 conglomerate. Lower Pliocene ?); T3, Masset volcanics (basalt flows and agglomerates. Pliocene ?). 



Idaho Batholith. The Idaho batholith is part of the Nevadan orogenic 

 belt, but at the same time it is closely associated with the Laramide 

 Rockies whose building occurred at a slightly later time. Because of the 

 complex geology around it the great pluton is treated separately in 

 Chapter 21. 



Late Cretaceous Phase 



The only Upper Cretaceous deposits of the Columbia system are con- 

 fined at present to a narrow belt along the northeast coasts of Vancouver 

 and Graham Island in the Queen Charlotte group. Although the belt is 

 narrow, the sediments have a thickness of 10,000 feet (Gunning, 1932). 



