THE PROBLEM OF THE ANORTHOSITES 99 



Norwegian Jabradoritites, nor in Tarassenko's^ monograph on the 

 labradoritites of Kiev, 



The problem of the anorthosites is not exhausted by an inter- 

 pretation of the anorthositic bodies. There still remain the 

 anorthositic bands in the banded gabbros of Scotland and the 

 Denejkin Kamen (the latter evidently unknown to Bowen). To 

 these bands the conception of an accumulation of solid crystals is 

 evidently not applicable, and the feldspathic, pyroxenitic, and 

 magnetitic (titanomagnetite) , as well as the leucocratic and melano- 

 cratic bands, must without doubt be considered as produced by 

 differentiation from the liquid state. The writer and Harker have 

 spoken of liquid immiscibility; I have further advocated the possi- 

 bility of liquation in consequence of assimilation; and we can 

 invoke other constituents coming into the magma during the 

 process of assimilation, or the absorption of gases that can produce 

 insolubility of a certain component and be therefore the cause of 

 its precipitation, like alcohol precipitating some substance form 

 an aqueous solution. All of these suppositions are only conjectures. 

 Experimental data are needed ; but there are certainly data favoring 

 the hypothesis of magmatic differentiation, and Bowen's hypothesis 

 is not applicable to the banded gabbros. 



In the Denejkin Kamen the ultrabasic rocks occur as small veins 

 and dikes in the gabbro. Their solidification was subsequent to 

 the consolidation of the gabbro and not the reverse as required by 

 Bowen's scheme. In Quebec (Chibougamau) according to Daly, 

 the hornblendite, pyroxenite and dunite cut the gabbro in dikes. 



Vogt, as is well known, has applied the eutectic scheme to the 

 interpretation of monomineral rocks. Bowen, on the contrary, 

 considers this scheme as inapplicable to igneous rocks because of 

 the widespread occurrence of solid solution. I think there is a 

 misunderstanding. Solid solutions and isomorphism are confined 

 to limited mineral groups, but the minerals of different groups, in 

 spite of being solid solutions, may be in eutectic relations. Con- 

 ceding to Bowen that it is not correct to speak of a eutectic mixture 

 of diopside and plagioclase, since the different plagioclases have 



' W. Tarassenko, "The Rocks of the Gabbro Family in the Radomysl and Shitomir 

 Districts of the Governm. of Kiev,"ilfem. Soc. Natur. Kijev., Vol. XV (1896), pp. 1-347. 



