lOO F. LOEWINSON-LESSING 



different fusion points, we can certainly speak of diopside-labradorite 

 (of a definite composition) eutectics, diopside-anorthite-eutectics, 

 etc. In certain cases the eutectic scheme is doubtless to be upheld. 

 For the rocks of granitoporphyric (holocrystalline-porphyritic) 

 texture I consider the eutectic rule as the leading factor in the 

 formation of phenocrysts. For instance, by measurements with the 

 Hirschwald ocular I have found that in diorite-porphyrite the 

 phenocrysts belong either to amphibole or to plagioclase depending 

 upon the predominance of the one or the other respectively over a 

 certain proportion, which is to be considered as the eutectic mixture, 

 quite as with alloys of metals or salts.^ 



Finally we must not omit the paragenetic relations of the great 

 anorthositic and pyroxenitic regions. The anorthosites of Canada, 

 Norway, and southwest Russia are connected with gabbro, norites, 

 and syenites. They belong to that type of the gabbro formation 

 which is united by intermediate members with syenites, and which 

 is not accompanied by pyroxenites and dunites. On the other 

 side the pyroxenites (Oural, America) and dunite are connected with 

 a more basic type of the gabbro group. In the Oural they are 

 accompanied by various ultrabasic types. There may be a certain 

 legality in these connections, but it certainly would be a forced 

 explanation should we say that in the Oural formations the anor- 

 thosites were destroyed by denudation, and that in Canada, Kiev, 

 etc., the denudation has not yet reached the pyroxenites. 



In regard to the paragenetic relations it is not to be lost sight of 

 that the pyroxenite and dunite occur in connection with gabbros 

 which contain the same minerals; alkaline pyroxenites are con- 

 nected with alkaline rocks, albitites, and andesine feldspatholites 

 with dioritic rocks, and labradoritites with gabbros. It is shown by 

 these peculiarities of paragenesis that the monomineral facies is 

 always formed by those minerals which are the characteristic com- 

 ponents of the corresponding mixed rock; that the differentiation 

 proceeds by the transfer of these minerals, which crystallized from 

 the original magma (Brogger and myself), and not by the transfer 



' F. Loewinson-Lessing and S. Zemcujny, "Porphyrartige Struktur und Eutektik," 

 Verhandl. Russ. Miner. Ges., 1906. (Experiments with salts and metallographic 

 photograms of them.) 



