1239 
and in a smaller degree, so that the quantity of it is small there. 
The boundary between the xenolith and the enclosing lava, of which 
the latter has adapted itself to the shapes of the crystals in the 
xenolith, proves moreover that the xenolith has not been enclosed 
at greater depth in a solid state, but that it has been taken up in 
the enclosing lava as a partly crystallized mass. | 
The “xenoliths mentioned sub 5 consist of plagioclase, augite and 
hypersthene with a few ore-crystals, the interspaces being filled up 
with various quantities of a partly devitrified, dark substance, against 
which feldspar-mierolites stand out sharply outlined. The plagio- 
clases and the pyroxenes present mostly idiomorphous outlines (espe- 
cially the plagioclases); in contradistinction to that of the xenoliths 
thus far described, the structure of the plagioclase is zonary with 
frequent alternation of more acid and basic zones, like those of the 
phenocrysts in the enclosing lava of the dome mentioned above. 
The xenoliths of older andesites mentioned sub 6, display differ- 
ences as regards mineralogical composition and structure. In some 
of them a few plagioclase phenocrysts occur in a groundmass, 
consisting of plagioclase and pyroxene with ore. 
In others amphibole was observed, occasionally as phenocryst in 
similar rocks to those mentioned above, sometimes in aureoles round 
orecrystals, occurring porphyrically with plagioclase in a dark glass- 
bearing groundmass. Frequently the microscopic aspect changes 
considerably, e.g. as to the amount of ore and as regards the colour 
of the groundmass, while the rocks give an impression of being 
modified through contactmetamorphism, in which process recrystalli- 
zations have taken place. The porphyrie plagioclases have been 
strongly eroded by the clear mixture of which the present ground- 
mass consists; we then suppose the groundmass to have been 
entirely recrystallized and the phenocrysts only in their marginal 
zone. The aureoles of amphibole round ore-erystals in a partly 
devitrified groundmass find an explanation in the assumption that 
what has taken place here is just the reverse of what happened 
with the resorption of amphibole. The enclosed andesite fragment, 
heated anew, has been for some time submitted to temperature- 
and  pressure-relations, which do not affect amphibole and this 
mineral has crystallized instead of components that otherwise build 
up resorption rims. 
The various erystallizations in the Galunggung magma. 
The boundaries of the homoeogeneous xenoliths relative to the 
enclosing lava proves that the xenoliths had not crystallized com- 
pletely when they were taken up in the lava. The residual magma 
