528 . THE VOGE 
only 4-5° below the melting-point of diopside. According to my 
earlier studies on slags, the individualization boundary between 
augite (CaMgSi,Os with some CaFeSi.Os, MgALSiOg, etc.) and 
olivine (Mg.SiO, with some Fe,SiO, and Mn,Si0,, consequently 
with a much lower melting-point than pure Mg,SiO,) lies at about 
70 per cent of augite:30 per cent of olivine. At this individuali- 
zation boundary a decrease of the melting-point appears according 
to experimental investigations., We accordingly here have to 
deal with a eutectic boundary-line between the two mix-crystals. 
The location of this boundary is chiefly dependent upon the com- 
position of the olivine, and this is probably due to the fact that 
the melting-point interval of the olivine is considerably lowered 
by some Fe,SiO,. . (See Fig. 22.) 
Regarding Mg,Si0,: MgSiO,, and especially with regard to the 
dissociation of MgSiO, at the pressure of one atmosphere and at 
high temperature (1577-1555°), some forsterite first being solidified 
from melted MgSiO,, we refer to Bowen’s investigations which 
are discussed in a following chapter. I here arrive at the result 
that the dissociation of MgSiO,, determined at the pressure of one 
atmosphere, cannot be transferred to apply to (Mg, Fe) SiO; or 
(Mg, Fe) SiO, at high pressure. 
In igneous rocks consisting of olivine and orthorhombic or 
monoclinic pyroxene, the olivine chiefly appears in idiomorphic 
individuals when the olivine forms at least one-third, and the 
pyroxene at most two-thirds. This fact is so well known that 
I find it superfluous to give special examples. But when the 
olivine is present only in small quantity, the sequence of crystalli- 
zation is quite turned about. Such rocks, with predominant 
pyroxene and quite little olivine, are in themselves rare, and 
furthermore the olivine in these rare rocks is only exceptionally 
fresh enough to permit a detailed study of the original structure of 
the rock. As far as I know, these rocks have not previously 
attracted any special attention; I shall therefore discuss a couple 
of examples. 
In a hypersthenite-norite from Nonaas-Litland in Hosanger, 
Norway (see analysis in the chapter on norites in Part II), a con- 
t See “‘Silikatschmelzlés.,”’ IT. 
