4IO 



REGINALD A. DALY 



actual number of its determinations in the respective group; "trace" 

 is taken to mean o.oi per cent. 



For the purpose of making a fair comparison among these averages 

 it is necessary to recalculate them all as anhydrous; for, clearly, a 

 large, though unknown, fraction of the v^ater entered in the hun- 

 dreds of analyses, must be regarded as mechanically absorbed 

 water. 



Table III, Columns 13, 14, 15, 16, and 17, shows these recalculated 

 averages. 



TABLE III 

 Recalculated Averages, Water Excluded 



13 



Olivine 

 Basalt 



14 

 Augite 

 Andesite 



15 

 Peridotite 



16 

 Limburgite 



17 

 Picrite 



SiO^.. 

 TiO^. . 

 AUO3. 

 FcjOs . 

 FeO... 

 MnO.. 

 MgO.. 

 CaO.. 

 Na^O. 

 K^O.. 

 P.O... 



49-65 



1-37 



16.16 



5-31 

 6.40 

 0.29 

 6.48 



9-30 

 3.10 

 1.48 

 0.46 



45.20 

 0.90 

 5-25 

 3-95 

 6.82 

 0.19 



29.70 



6.43 

 0.65 

 0.77 

 0.14 



Sum, 100 . 00 in each case. 



Table IV, Column 18, indicates the average composition of the 

 olivine phenocrysts in basalt, according to Rammelsberg.' Column 



TABLE IV 

 Composition of Phenocrysts in Olivine Basalt 



I Quoted in Zirkel's Lehrbuch der Peirographie, 2d ed. (1893), Vol. I, p. 353. 



