( 411 ) 



of the MgO and the CaO quantity. The mode deviates rather consi- 

 derably from the norm by the presence of biotite and amphibole, 

 which minerals have to be considered as the bearers of the MgO, 

 which is put here under the enstatite-molecule. A portion of the 

 MgO, however, also occurs in the augite and the amphibole of the 

 resorption-border and in the chlorite. 



The molecular proportions calculated on a sum of 100 — Fe 

 reduced to FeO — yield : 



SiO a A1 3 3 FeO MgO CaO Na,0 

 69.34 10.68 3.85 4.18 5.77 4.38 



K,0 



1.26 



TiO, 

 0.53 



Formula according to Osann : 



s 

 69.87 



A C F a c 



5.64 5.05 8.75 5.8 5.2 



f n in k 

 9 7.7 9.2 1.33 



Series 

 a v 



(8.7) (7.8) (13.5) 



In the graphic notation it is the basic character which, by the 

 side of the close similarity between the two preceding dacites, is 

 distinctly expressed. To make a comparison we give here the analyses 

 of some chemically closely allied rocks : 



III 



IV 



SiO, 

 A1,0., 



FeA 



FeO 



MgO 



CaO 



Na 2 



K 2 



H 2 0+ 



HoO- 



TiO, 



P 2 6 



MnO 



BaO 



62.78 

 17.16 

 1.96 

 2 31 

 2.32 

 4.84 

 4.11 

 2 15 

 0.88 

 0.24 

 (t r,C, 

 0.15 

 n. in; 

 0.04 



Som 



02 . 70 

 16.37 



2.81 

 1 62 

 2.50 

 4.84 

 4.05 

 1.83 

 1.79 

 (l. 87 

 0.01 



62.27 



16.92 



2.40 



2.59 



2.87 

 4.78 

 4.72 

 1.47 

 1 .22 



0.16 



sp. 



99 58 '100.02 99.47 



62.09 

 17.03 

 2.38 

 2.69 

 3.08 

 5.65 

 4.10 

 1.67 

 0.13 

 0.04 

 0.65 

 0.19 

 sp. 

 0.07 



62.09 

 16.69 

 1.45 

 3.76 

 1.93 

 6.08 

 3.30 

 1.84 

 I .47 

 0.19 

 0.32 

 0.39 

 sp. 

 0.10 



VI 



61 .22 

 16.14 

 3.01 

 2.58 

 4.21 

 5.46 

 4.48 

 1.87 

 0.40 

 0.04 

 0.61 

 0.25 

 sp. 



'.9.84 



99.77 



100.36 



