568 
among the phenocrysts of the voleanic rocks. This points to consider- 
able mineralogical differences between the volcanic rock and the 
xenoliths, which in this case, unlike the homoeogeneous xenoliths of 
the amphibole andesites from the Hifel, cannot be explained merely 
by segregation. 
We are safe to assume that in the lower parts of the voleano 
various mineral-combinations have been crystallized from the magma 
in various places. In the magma, which came to effusion at various 
epochs, the phenocrysts of the voleanic rock were crystallized in 
the intratelluric period. The magma that procured the numerous 
amphibole-bearing xenoliths, has more or less perfectly been crystal- 
lized, while fragments were carried along by the escaping magma. 
The occurrence of glass in some of these xenoliths proves that erys- 
tallization was not yet quite terminated when the effusion took place. 
The mostly non-resorbed condition of the amphibole in these glass- 
bearing xenoliths in loose volcanic products and not in solid lava 
indicates that the resorption of the amphibole has begun during the 
effusion and the enclosing by the magma of the hypersthene augite 
andesites. In the parts of the enclosing lava that have cooled down 
rapidly we generally find the amphibole unresorbed or only very 
little resorbed; in the lava that has cooled down slowly and in the 
dome we find it much more or completely resorbed. 
Hardly any differentiation of the magma in the lower regions 
of the voleano need be made; once more we point to the constant 
composition of the voleanic rocks of different eruptions. The am- 
phibole-bearing xenoliths represent the sometimes slightly more 
basic, dioritie equivalents of the andesitic effusive rocks. There 
are several indications that, in general, in a crystallizing magma, 
augite represents the stable phase at a higher, amphibole that at a 
lower temperature. Also, that the development of the complex amphi- 
bole-molecule is rendered possible only in the presence of gaseous 
components in the magma. The complex molecule, stable only under 
definite circumstances, is replaced by simpler combinations, when 
conditions are changing, e.g. through escaping of the gases and 
diminution of pressure, as proved by the widely spread resorption 
phenomena of the amphibole in volcanic rocks, which have been 
described heretofore. This resorption does not take place if the 
cooling occurs very rapidly; this accounts for its absence in the 
amphiboles of the xenoliths enclosed by loose voleanie products or 
which occur as isolated fragments in tuffs. 
The occurrence of olivine in some xenoliths also constitutes a 
mineralogical difference with the effusive rocks that enclose them. 
