4i6 /. H. L. VOGT 



monomineralic^ rocks, must, as explained in an earlier paper^ 

 generally, both absolutely and relatively, have been very Uttle. 

 We will, therefore, get only a small lowering of the temperature 

 of crystaUization on account of H2O, CO2, etc., in these rocks). 

 Since the anchi-monomineralic rocks are always characterized by 

 the presence of a mineral with a rather high melting temperature — ■ 

 such as labradorite, bytownite, olivine, orthopyroxene, diopside 

 poor in iron, further nephehne, leucite, ilmenite, etc.,^ — -in so rich 

 a quantity (as at least about 90 per cent) that the other components 

 only bring about a rather smaU lowering of the melting point, the 

 result will be that these anchi-monomineralic rocks generally have a 

 high temperature for the beginning of the crystallization, and this 

 temperature is considerably higher than for the anchi-eutectic. 



Regarding the temperature of the conclusion of the crystalliza- 

 tion, for instance in anorthosite and norite, on the other hand, we 

 will have fair identity. There is this difference, however, that the 

 eutectic end-magma of the anorthosites is present in a small quan- 

 tity, while that of the norites is present in considerable abundance. 



As we shall explain in a later paper, the high temperature at 

 which the magmas of anorthosites and peridotites start to crystallize 

 has a very important geological significance, because in my opinion, 

 this causes these rocks never to appear as effusives, and causes 

 the anorthosites — probably the dunites too — ^to be formed only 

 in very deep-seated magma-basins. 



For the anchi-eutectic magmas we may suppose a somewhat 

 larger content of H2O, CO2, etc., and this content, as explained 

 earlier"* must have been relatively large, especially in the deep-seated 

 granitic magmas. 



' The sulphide ore segregations of typus Sulitjelma and Roros will not be con- 

 sidered here because these, as to the physico-chemical conditions of the genesis, occupy 

 a separate place. See my resume- treatise. Die Sulfid-Silikatschmehmassen, 1918, p. 245, 

 and the detailed description by Th. Vogt in his monography on "Sulitjelma" (Norw. 

 Geol. Survey, now being printed) . 



2 This Journal, 1922, p. 667-668. 



^Here is not taken into consideration the segregation of nickel-pyrrhotite, with 

 a relatively low melting temperature. 



4 See this Journal, 1922, p. 670-71. 



