Reviews 



The Okanagan Composite Batholith of the Cascade Mountain System. 

 By Reginald A. Daly. (Bulletin of the Geological Society of 

 America, Vol. XVII, pp. 329-76, 1906.) 



This batholith is on the international boundary between British Colum- 

 bia and the state of Washington. Its east-west dimension is about sixty 

 miles; the north and south limits are not known. The batholith is compos- 

 ite, the individual intrusions having been made from late Paleozoic to late 

 Tertiary time. There is considerable variation petrographically in these 

 intrusions, the later ones being as a whole progressively more acid, but the 

 series was broken near the close of the Laramie by the intrusion of some 

 alkaline syenites and malignite. The small Paleozoic bodies are a complex, 

 variable, highly metamorphosed series of gabbros, peridotites and dunite. 

 The Jurassic batholiths are of granodiorite, and the Tertiary batholiths are 

 of biotite-hornblende-granite and biotite-granite. There are a few dikes of 

 olivine basalt, thought to be of Pleistocene age. 



It is evident from Daly's descriptions that these rocks are in general 

 accord with the rest of the Pacific Coast petrographic province in their 

 moderately high ratio of soda to potash. 



In Lower Cretaceous time the Jurassic granodiorites had been exposed 

 by erosion, and over 30,000 feet of arkose sandstones, grits, and conglomer- 

 ates were deposited on them. This was followed by deformation, which 

 resulted in the production of faults and folds in the Cretaceous strata, with 

 dips averaging over 45°. Probably at the same time the granodiorites 

 were sheared and crushed into banded gneisses and gneissic granites. 



The method of batholitic intrusion by replacement is discussed, and an 

 ideal skeleton history of a batholite is given. 



c. w. w. 



Crescentic Gouges on Glaciated Surfaces. By G. K. Gilbert. (Bulle- 

 tin of the Geological Society of America, Vol. XVII, pp. 303- 

 16; Pis. 37-39. 1906.) 

 The chatter-mark and crescentic crack are described. The former 

 is thought to be due to the slow, rhythmic striking of bowlders embedded 

 in the basal ice. Fracture results, if the surface of the rock is under tension. 



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