270 



GEOLOGY. 



Lake and other terrestrial deposits, largely of volcanic material, 

 are known north of the United States, especially in that part of 

 British Columbia 1 between the Coast and Gold ranges. The volcanic 

 centers seem to have been numerous, and along the eastern base of 



Fig. 448. — Smokestack Rock. Conglomerate in the Arikaree formation of western 

 Nebraska. (Darton, U. S. Geol. Surv.) 



the former range. Miocene deposits are known as far north as the 

 Francis River, and also on the Porcupine branch of the Yukon; but 

 erosion rather than deposition was the dominant process in Alaska, 

 so far as present data show. 



Igneous activity during the Miocene. — The wide-spread igneous 

 activity which began with the close of the Cretaceous and continued, 



folios of the U. S. Geol. Surv. Both sedimentary and igneous formations are reprc 

 sented. 



1 Dawson, G. M., Trans. Royal Soc. of Canada, 1890. 



