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corundum-syenite a magma supersaturated with alumina. Alumino- 

 silicate magmas are thus divided into two great analogous groups, each 

 of which is subdivided into three types, as follows : 



GROUP A 



i. Magmas supersaturated with Al 2 3 . 



2. Magmas saturated with A1 2 3 . 



3. Magmas not saturated with A1 2 3 . 



GROUP B 



1. Magmas supersaturated with Si0 2 . 



2. Magmas saturated with Si0 2 . 



3. Magmas not saturated with Si0 2 . 



In both groups type 2 is the same, a syenite or trachyte magma, 

 simultaneously saturated with both alumina and silica. There are thus 

 five principal types in all, as follows : 



1. Magma supersaturated with alumina: corundum-syenite, bearing 

 alkaline feldspars, and kyschtymite bearing lime-soda feldspars. 



2. Magma supersaturated with silica: granites, rhyolites, qusrtz- 

 diorites, dacites, etc. 



3. Magma saturated simultaneously with alumina and silica : mica- 

 syenite, trachyte, mica-diorite, and mica-andesite. In this magma the 

 aluminosilicates are the essential minerals. The pure metasilicates and 

 orthosilicates are accessory or absent. 



4. Magma not saturated with alumina : gabbro, basalt, diabase 

 pyroxenite and other basic rocks. Obviously this magma is also not 

 saturated with Si0 2 . 



5. Magma not fully saturated with Si0 2 : elaeolite-syenite, phono- 

 lite, leucitite, etc. 



The magma types 4 and 5 are not identical. A biotite-elaeolite- 

 syenite can be saturated with A1 2 3 and not fully saturated with Si0 2 . 

 In the same way some nepheline rocks may be considered as saturated 

 with A1 2 3 , but do not contain sufficient silica to develop free quartz. 

 In the above scheme it is of course obvious that the rocks belonging 

 to the first type of Group A are least widespread according to our pres- 

 ent knowledge of the geology of the earth, and will be discovered, in 

 the opinion of the author, in greater quantity in the future. 



It will be seen that in these experiments all the essential minerals 

 of the "neovolcanic lavas" have been reproduced with the exception 



