Yol. 55.] RHTOLITES OF THE HAUEAKI GOLBFIELDS. 



4^7 



microscopic characters of the ' Eruptive Rocks of New Zealand/ 

 but the paper by Capt. Hutton, bearing that title, is replete with 

 references to their works up to 1889, and during the past ten years 

 much has been added to this branch of geological literature. 



Part III. — Analyses of the Rhyolites. By Philip Hollanb. 



The rocks H^ from Omahu and H^^ [191] from Grand Junction 

 Mine, 100-foot level, Waihi, both of them described in this paper 

 (pp. 451 & 460), have been analysed. Moreover, analyses of three 

 rhy elites from the United States, copied from Bull. No. 148, U.8. 

 Geol. Surv, pp. 131 & 192, are placed beside these analyses of 

 Hauraki rhyolites for comparison, since in some respects they closely 

 resemble them. Nos. Ill & IV are by W. F. Hillebrand, and 

 No. Y by J. E. Whitfield. 



No. Ill is the analysis of a rhyolite a short distance north- 

 west of Willow Lake, near the Geyser, Plumas County, California. 

 No. IV is that of a rhyolite from near Slate Creek, west of 

 Deer Creek Meadows, California. No. Y is of a rhyolite from 

 Mount Sheridan. 



A small amount of biotite is stated to be present in No. IV, and 

 a little augite in No. Y. 



In Nos. I & II the finely-powdered rock was dried at 100° C. 

 before analysis, and in Nos. Ill & lY the materials were dried at 

 110° C. 



In the Hauraki rhyolites (Nos, I & II), a very small amount of 

 pyrites was detected under the microscope. 



Omahu. 

 SiO., Silica 77-59 



Fe.^Og Ferric oxide... 



FeO Ferrous oxide. . . 



MnO Manganese 1 



oxide J 



II. 



Waihi. 



73-08 



13-50 



2-60 



•13 



trace trace 



•67 

 none 



CaO Lime 



•63 



•04 



BaO Baryta '10 



MgO Magnesia •16 



K2O Potash 3^99 



Na^OSoda 2-56 



PgOg Phosphorus 1 trace ... 



pentoxide J .q« 

 SO3 Sulphur trioxide 



H2O Water ■. 1-54 ... 



•62 

 1^07 



•06 



•15 



319 



3-95 



.. trace 

 .. 12 

 .. 1-33 



10010 



III. IV. V. 



Willow Slate Mount 

 Lake. Creek. Sheridan. 



74-24 



14-60 



1-27 



-67 



•06 



73-64 



13-44 



•60 



•74 



•06 



•20 •ll 



•11 r26 



SrO Strontia -02 



•18 



•25 



3-66 



3-00 



•07 



•03 



2^04 



•11 



•26 

 4-50 

 3-51 



75-89 



12-27 



M2 



1-37 



•50 



•29 

 3-42 

 3^23 



Lij^O Litbia •Ol 

 •06 none 



none 

 1-99 



•28 



•82 



99-80 100-28 100-30 100-06 



Specific gravity =2*5 11. =2514. 



[lu Analyses I & II strontium and lithium were not sought.] 



2h2 



