0-185 



0-28. 



0-3S3 



252 Prof. F. Loewinmn-Lessing — Origin of the Igneous Rocks. 



wichtige Thatsache noeh einrnal zu betonen, die reinste ungespaltene 

 Form des tellurischen Magmas dar. Darin liegt ihre hoheBedeutung." 

 He emphasizes also his opinion that the monzonitic magma is subject 

 to large differentiation processes. 



The following calculations show clearly that the monzonite and the 

 essexite differ more from the average magma than the syenite : — 



TABLE IV. 

 Monzonite (after the latest calculations of Daly) — 



% Molecular Ratios. 



SiOa . . 56'74 . . 0-946 

 A1 3 3 . . 16-97 . . 0-166 \ 



Fei0 3 . . 3-11 . . 0-019 ) 

 FeO . . 4-64 . . 0-064 

 MgO . . 4-31 . . 0-108 

 CaO . . 6-12 . . 0-110 ) 



Na,0 . . 3-57 . . 0-057 I 



K 2 . . 4-22 . . 0-044 ) 

 3-8 RO 1-9 R2O3 9-5 SiOa or 2"07 RO R2 O 

 a= 2-01. R2O : RO = 1 : 2'8. 

 Monzonites after Brogger l — 



2-34 RO R2O3 5-05 Si0 2 . 

 o = 1-91. £ = 55. 

 R2O : RO = 1 : 3-3. 



We can readily see that this magma is not more like the average 

 one than is that of the syenite ; the average magma is rather the 

 mean between the monzonitic and the syenitic magmas (except as 

 regards silica and the relation ]! 2 0:RO). This magma in reality 

 much resembles that of the syenite, and if we take my earlier formula 

 for the gabbro-syenites (= monzonites), the difference between this 

 magma and the average will appear even more evident. 



The essexitic magma presents even less resemblance to the average 

 terrestrial. magma, as can be shown by the following calculations: — 



TABLE V. 

 Essexite (after the latest calculation of Daly) — 



Molecular Ratios. 

 SiO a • . 50-02 . . 0-834 



0-101 ) 



5-11 Si0 2 . 



A1 2 3 

 FeoOa 

 FeO 

 MgO 

 CaO 

 Na 2 

 KoO 

 4-4 RO 2-1 Ro 



17-58 . 



538 . 



6-50 . 



4-72 . 



7-40 . 



4-68 . 



2-23 . 

 8-3 Si0 2 or 



0-172 I 

 0-034 )' 

 0-090 



0-118 \ 0-340 

 0-132 ) 

 0*075 ) 

 0-024 ) 

 2-1 RO R 2 3 4 SiOz. 



0-206 



0-099 



0-439 



a = 1-58. RiO:RO = 1:34. 

 This magma corresponds to the vogesitic magma, and approximates 

 to the syenito-dioritic one, but is very different from the terrestrial 



1 W. Brogger, Die Eruptivgesteinc des Kristianiagebiets. II. Die Erup- 

 tionsfolge cler triadischen Eruptivgesteine bei Predazzo. 1895, p. 27. 



