236 KEMP'S ORE DEPOSITS. 



1867; also Zeitschrift d. d. yeol. GeselL, 1868, 663), distinguished 

 in the Washoe district syenite, metamorphic rocks, quartz-por- 

 phyry, propylite, sanidine-trachyte, and very subordinate andesite. 

 Mr. King referred much of the propylite of Yon Richthofen to 

 andesite, but retained the propylite as a distinct species, although 

 remarking the close affinities of the two. The quartz-porphyry he 

 called quartz-propylite. In other respects no changes are intro- 

 duced. Zirkel (Fortieth Parallel Survey, Vol. VI.) determined 

 the syenite as granular diorite, and while accepting hornblende- 

 propylite and quartz-propylite as separate species, the greater part 

 of the quartzose rock he called dacite. He introduced for the 

 first time augite-andesite, rhyolite, and basalt. Mr. Church paid 

 less attention to lithology, and used the terms of his predecessors 

 somewhat loosely. Mr. Becker makes the following classifica- 

 tion : granular diorite, porphyritic diorite, micaceous diorite- 

 porphyry, quartz-porphyry, earlier diabase, later diabase, earlier 

 hornblende-andesite, augite-andesite, later hornblende-andesite, 

 and basalt. In this it will be seen that several new varieties are 

 introduced, but the main mass of Mount Davidson was still con- 

 sidered diorite, and the vein was thought to lie between this and 

 some of the other species mentioned, especially diabase. In 1885, 

 Arnold Hague and J. P. Iddings completed new microscopical 

 studies upon the materials collected by Mr. Becker, and the re- 

 sults were published as Bulletin 17 of the United States Geologi- 

 cal Survey ("On the Development of Crystallization in the 

 Igneous Rocks of Washoe," etc.). These two writers had had 

 more to do with the eruptive rocks of the Great Basin and the 

 Pacific slope than any other geologists, and hence brought to the 

 review an exceptional experience. Nowhere else in the world are 

 such exposures and thorough sections afforded, alike in depth and 

 in horizontal extent. They proved that the diabase and augite- 

 andesite shade into each other, the differences in crystallization 

 being due to depth ; that the hornblende of the so-called diorite 

 was largely secondary from original augite, being derived by 

 paramorphic change (uralitization), and that the diorite was a 

 structural variety of the diabase ; that the porphyritic diorites 

 shade into the earlier hornblende-andesites and are structural 

 varieties of them ; that the mica-diorites and hornblende-andesite 

 are identical in the same way ; that the assumed Pre-Tertiary age 

 of the quartz -porphyry was unwarranted, and that it was partly 

 dacite and partly rhyolite, the two shading into each other ; that the 



