ANALYSES OF ROCKS. 



601 



These figures correspond almost perfectly with percentages of the same oxides in 

 the anah^ses of obsidian and pumice from Lipari.* It is interesting in this con- 

 nection to note that Abichf has described a liparite from within the crater of 

 Volcano which contained 70.50 per cent of silica. 



Mineralogically, then, this rock resembles most the trachytes, but as anorthoclase 

 takes the place of sanidine, it should, therefore, be classed with the pantellerites. 

 The phenocrysts are in two generations, and are anorthoclase, andesine, acmitic 

 augite and olivine. The only accessory minerals are magnetite and microlitic 

 apatite needles. The Michel-Levy formula for this rock would then be : 



r/i — {F1.0){0P^)a,ti. 



A small fragment of the outer rim of a f)rojectile as free from vesicles as any that 

 could be found was determined to have a specific gravity of 2.42. 



Some fragments of both the pumiceous core and the glassy rim of a projectile 

 were taken and, after picking out the doleritic inclusions, subjected to a complete 

 chemical analysis. The results of this analysis, which was kindl}^ made for me by 

 Mr Louis Kahlenberg, instructor in chemistry in the University of Wisconsin, are 

 printed under. I in the following table. In columns II to VI are piinted other rock 

 analyses for comparison. 





I. 



II. 



III. 



IV. 



V. 



VI. 



Si(\ 



66.99 

 17.56 



1.41 



3.39 

 trace 



4.25 

 .93 



3.35 

 .34 



1.53 

 trace 



66.41 



17.41 



4.12 



""3.96' 



1.82 



3.83 



1.65 



.81 



67.19 



16.96 



3.45 



1.20 



trace 



4.46 



1.50 



3.70 



1.55 



.89 



66.3 



17.8 



2.4 



.4 



63.2 



16.3 



1.8 



2.1 



69.0 



A1,0, 



10.1 



Fe.,0^ 



4.4 



FeO 



4.6 



MnO . . . 





CaO 



2.1 



.3 



5.6 



3.5 



.2 



3.6 

 L9 

 2.5 

 6.0 

 2.3 



L5 



MgO 



.8 



NaaO 



6.3 



K2O 



3.7 



H,/) 





P.,C)= ... 





' 2^'5 



Others . . 







1.3 



1.0 



.3 















99.75 



100.01 



100.88 



99.9 



101.0 



100.7 



I. Total analysis of the Volcano projectiles of 1888. 

 U. Felso-dacite from Rodua, Siebenbiirgen. X 



III. Dacite from Nagy Sebes, Siebenbiirgen. g 



IV. Domite from the Puy de Dom, Auvergne. 

 V. Trachyte from INIonte Amiata. || 



VI. Pantellerite from Cuddia Mida, Pantelleria. 1[ 



* J. Roth : Die Gesteinsanalysen, p. 11. 

 fAbich: Vulkanisohe Erscheiniingen, 18-41, p. 26. 

 tDoelter: Tseherm. min. Mitth., vol. iii, 187;^, p. 74. 



gCf. Ibid., p. 93. This rock is the type of dacite cited by Rosenbusch (Ueber die chemischen 

 Beziehungen der Eruptivgesteine, ibi'i., N. F., vdl xi, 1890, p. 178). 

 II J. F. Williams: Inaugural Dissertation, Stuttgart, 1887, p. 33. 

 ^ Forstner : Zeitsch. f. Kryst., vol. viii, 1883, p. 182. 



