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SCIENCE PROGRESS 



been chosen as possible. In making the selection much 

 assistance has been afforded by H. S. Washington's valuable 

 collection of analyses. 1 



The Calc-Alkali Series 

 Table of Analyses of Rock-types 



I. Granodiorite, Indian Valley, Sierra County, California. W. F. Hillebrande. 

 Quoted in H. S. Washington's Chemical Analyses, p. 179. 

 II. Tonalite, Wistra, Carinthia, Austria. H. Krezmar. Quoted in H. S. 

 Washington's Chemical Analyses, p. 193. 



III. Quartz-diorite, Tuolumne River, Amador County, California. W. F. Hille- 



brande. Quoted in H. S. Washington's Chemical Analyses, p. 237. 



IV. Diorite. Brogger's average of sixteen analyses of typical diorites. Die 



Triadische Eruptionsfolge bei Predazzo, loc. cit. Christiania, 1895, p. 36. 

 V. Gabbro. Broadford Boss, Skye. T. Baker. Quoted by Harker, The 

 Tertiary Igneous Rocks of Skye, Mem. Geol. Surv., 1904, p. 103. 



It will be seen that, of these five analyses, the silica per- 

 centages of the two extremes place the rocks outside the limits 

 of the Intermediate Group— that is to say, granodiorite is a 

 member of the Acid, and gabbro a member of the Basic Group ; 

 while tonalite, quartz-diorite, and diorite are Intermediate rocks. 

 In the diagram (fig. 2) the molecular proportions of the silica 

 and bases are shown by the Iddings method. In this diagram 

 it will be recognised as a general characteristic of the series 

 that while the molecular proportion of lime is high, that of 

 the alkalies is low, and especially is this true with regard to 

 the potash, which is much lower than the soda. At the basic 



1 Chemical Analyses of Igneous Rocks, published from 1884 to 1900. U.S. 

 Geol- Survey Prof. Paper No. 14, Series D and E, 1903. 



