Vol. 65.] WITH POKPHYKITIC LABRADORITE-CRYSXALS. 101 



The hypersthene or enstatite-hypersthene, separated out in the 

 presence of a fairly large quantity of Ca(Fe, Mg)Si 2 6 , contains, 

 at the high temperature at which the mineral is formed, about 

 12 to 15 per cent, of CaMgSi 2 e or CaFeSi.,0 G . By cooling down to 

 ordinary temperature, however, the enstatite-hypersthene cannot 

 carry so much Ca(Mg, Fe)Si 2 O e in solid solution. Consequently 

 some augite is separated out, in perthitic lamellae — corresponding 

 with the perthitic lamella? of albite or albite-oligoclase in perthitic 

 striated microcline. I would refer the reader to my explanation 

 regarding this phenomenon in Tscherm. Min. Petrogr. Mitth. 

 vol. xxiv (1905) pp. 541-42 (and fig. 10, compare the lines J N 

 & GM, p. 484) and to the later published work of Dr. W. Wahl, 

 ' Analogien zwischen Gliedern der Pyroxen- & Feldspat-Gruppen 

 & iiber die Perthitstrukturen/ 1 



Further, I would remark that the materials of the well-known 

 microlithic interposition — of titanium mineral(?) — in the plagioclase 

 as well as in the diallage and hypersthene of the gabbro-rocks most 

 probably were contained at first in solid solution, and that they 

 separated out on the later cooling down. 



On the temperature-interval of the crystallization. — 

 In a solution consisting only of anorthite and albite, of composition 

 58-5 An : 41-5 Ab, the point P (see fig. 4, p. 97) will, under a 

 pressure of one atmosphere, lie at about 1475° Centigr. When 

 some orthoclase is present in the solution, namely with the pro- 

 portion 55 An : 39 Ab : 6 Or, the surface of crystallization will be 

 reached at a little lower temperature, namely, at about 1450° (see 

 fig. 12 of my paper in Tscherm. Min. Petrogr. Mitth. vol. xxiv, 1905, 

 p. 506). Considering the lowering influence exercised by the many 

 other components on the plane of crystallization, we may assume 

 that the crystallization of the plagioclase in the rock here described 

 ought to have begun at a temperature of about 1350° or 1350° to 

 1400° Centigrade, presuming crystallization to have taken place at 

 low pressure. And the end of the crystallization at the eutectic 

 finally reached might be taken to lie at about 1000°. Actually 

 the crystallization took place under a very high pressure ; thus 

 the crystallization-temperatures in question were raised, the increase 

 being, however, rather small — as I have explained in an earlier 

 paper (in Tscherm. Min. Petrogr. Mitth. vol. xxvii, 1908). The 

 real interval of crystallization for the rock here described may thus 

 be placed in the stage between about 1400° and about 1000°- 

 1050°. 



In my earlier works above cited, it has been my chief object to 

 show that the ordinary physico-chemical laws applying to the phases 

 liquid-solid also hold good as regards the processes of crystallization 

 in magmas. 



1 Ofvers. af Finska Vetensk. Soc. Forh. 1906-1907, printed 1908, No. 2, 

 p. 19. 



