90 F. LOEWINSON-LESSING 



spathic fades. ^ Vogt referred the formation of the monomineral 

 rocks to the eutectic scheme, and contrasted the "anchimono- 

 mineral" rocks with the "anchieutectic." Daly applied his view- 

 on gravitative differentiation and his eclectic theory of the origin 

 of the igneous rocks (which is essentially, as he himself states in his 

 admirable and highly suggestive book, Igneous Rocks and Their 

 Origin, a further development of my syntectical-liquational theory) 

 to monomineral rocks. In. the conceptions of Vogt, Daly, and the 

 writer the formation of monomineral rocks is intimately connected 

 with magmatic differentiation in the Hquid state. Bowen, on the 

 contrary, on the basis of his important and suggestive laboratory 

 experiments, attributed the formation of the monomineral rocks to 

 differentiation by crystallization. He considers these rocks as 

 resulting from a gravitative accumulation of crystals in the early 

 stages of the crystallization of a basaltic magma. The essential 

 difference between Vogt, Daly, and myself on the one side, and 

 Bowen on the other, is that according to us the monomineral rocks 

 existed as such in the liquid state, while Bowen does not admit the 

 existence of a monomineral rock in the liquid state. He considers 

 such rocks only as gravitational accumulations of soHd crystals 

 during the crystallization of a basaltic magma.^ For the anortho- 

 sites of southwest Baikal, Switalsky presented a third view. He 

 thought that all of these rocks ". . . . originated from a liquid 

 mass," but they were formed from sedimentary materials; the an- 

 orthosites, granites, monzonites, and gabbros by fusion of the 

 sediments, and the crystalline schists by recrystallization in the 

 solid state.^ 



The peculiar characteristics of the anorthosites are the enor- 

 mous dimensions of certain anorthosite bodies, their presence 

 exclusively among plutonic rocks and the absence of their effusive 

 equivalents, the frequently occurring extreme coarseness of grain, 



' F. Loewinson-Lessing, " Kritische Beitrage zur Systematik der Eruptivgesteine. 

 IV. Ueber mbnotektische (ungemischte) Magmen," Tscherm. Min. MUt.,XX, p. 15. 



= N. L. Bowen, "The Later Stages of the Evolution of the Igneous Rocks," Jotir. 

 Geol., Suppl. to Vol. XXIII (1915); "The Problem of the Anorthosites," ibid., Vol. 

 XXV (1919), p. 209. 



^N. Switalsky, "The Anorthosite Rocks and the Pyroxenic Crystalline Schists of 

 the Southwest Baikal Region," Bull. Com. Geol. de Russie (1915), p. 999. 



