COMPARISON WITH SIMILAR ORE DEPOSITS ELSEWHERE. 275 



PROBABLE STILL FURTHER EXTENSION OF THE GREAT BASIN- 

 MEXICO PETROGRAPHIC PROVINCE. 



In 1902 the author" recalled his description of the petrographic province, 

 which includes the volcanic region of Nevada, and noted the work of Ordonez. 

 He also called attention to the fact that later developments showed similar lavas 

 of similar age and succession in localities in the State of Washington and on the 

 California coast. His statement was as follows: 



" Without being in danger of carrying this correlation to excess I may point 

 out that the Pliocene olivine-basalts of the Sierra Nevada* are abundantly present 

 in Oregon and Washington; that the British Columbia basalts are approximately, 

 at least, of the same period/ and that throughout the whole of Alaska and into 

 the Bering Sea occur olivine-basalts of Pliocene age.'' 



" Again, the abundance of basic andesities (typically augitic, often hypersthene- 

 bearing, and verging toward basalts) all belonging to one epoch (very late 

 Pliocene-Pleistocene), in a continuous belt in Alaska, running the whole length of 

 the Aleutian Islands and peninsula, turning the same angle as the chief orographic 

 and topographic features, and running down the coast past Sitka; e the occurrence 

 of the same rocks, belonging to the same age, in Washington and Oregon 

 (Mount Rainier, etc.); the extension of the belt through the Sierra Nevada 

 and along the western part of the Great Basin; finally its extension into Mexico-'' 

 this is all striking and deserves recognition. Moreover, this belt of late Pliocene- 

 Pleistocene augite (hypersthene) andesites extends through Central and South 

 America, in the Andes. 9 ' In Alaska and in the Andes some of the cones of this 

 epoch are still active, but the majority have become extinct. 



"It appears, then, that the whole extreme western part of the western 

 hemisphere (the Pacific coast of the Americas) is a zone occupied by what (at some 

 periods, at least) is and has been a single petrographic province. 



"It remains to be seen whether this province is not continued into Asia with 

 the change of erogenic trends in Alaska from northwest to southwest. The line of 

 late Tertiary-Pleistocene volcanoes, which extends along the Aleutian Islands to 

 Kamchatka, is represented by 15 or 20 cones in this peninsula; this line, following 

 the general erogenic trend, runs southwest through the Kurile Islands, the islands 

 of Japan, and the Philippines, into the East Indies. Andesites largely pyroxene 

 andesites, and frequently hypersthene andesites are characteristic of this chain also, 

 as far as the famous volcano of Krakatua." 



ngpurr, J. E., Trans. Am. Inst. Min. Eng., vol. 33, pp. 332-333. 

 fcSpurr, J. E., Jour. Geol., vol. 8, No. 7, chart, p. 643. 



cDawson, G. M., Ann. Kept. Geol. Nat. Hist. Survey Canada, vol. 3, pt. 1, p. 37, B; also, Trans. Royal Soc. Canada, vol. 8, 

 sec. 4, p. 15. i 



<i Spurt, J. E., Geology of the Yukon gold district. Eighteenth Ann. Kept. U. S. Geol. Survey, pt. 3, p. 250. 

 < Spurr, J. E., Reconnaissance in southwestern Alaska, Twentieth Ann. Rept. U. S. Geol. Survey, pt. 7, map 13. 

 1 Ordonez, Ezequiel, Las rhyolitas de Mexico, Boletin del Institute geo!6gico de Mexico, No. 14, p. 66. 

 uZirkel. Lehrbuch d. Petrographie, 2d ed., vol. 2, pp. 831-832. 



