567 
of augite, while only some of the colourless constituents can with 
certainty be said to be plagioclase. Also with stronger resorption the 
amphibole changes into a mixture of the three named minerals. An 
enclosure of the lava flow of 1904, which chiefly consists of plagio- 
clase and brown amphibole with few large augite- and hypersthene 
crystals, shows around, and also in veins running through the 
amphiboles, a mixture of hypersthene, augite and plagioclase, which 
also occurs isolated in the parts of the amphibole that have not 
been altered completely. The margin round the amphiboles becomes 
very rich in ore in the outer rim, so that the three minerals are 
found here in a more zonary arrangement. 
Numerous xenoliths are characterized by completely resorbed 
amphiboles. Sometimes they consist entirely of a combination of very 
small ore-crystals. In others pyroxene (chiefly certainly augite) and 
also sometimes plagioclase occur in great quantity with the ore. 
They were found in xenoliths from the south-eastern part of the 
island, together with plagioclase and much light-brown glass without 
microlites. For the rest most of the xenoliths collected from the lava 
dome of 1904 are characterized by totally resorbed amphiboles, which 
contain besides plagioclase only little augite and hypersthene, just as 
is the case with a few xenoliths of the latest eruption-products 
(eruption of 1914). 
Origin of the xenoliths. 
The volcanic magma that has reached the earth’s surface during 
the several eruptions, presents a very constant mineralogical compo- 
sition; the lava (as a flow, or as a dome) as well as the loose vol- 
canie products are principally hypersthene augite andesites. The 
sporadic amphibole-crystals in some rocks are in part and perhaps 
all to be considered as xenoliths of one mineral only *). For xeno- 
liths, consisting of mineral-combinations, which also occur as pheno- 
erysts in the enclosing rocks with or without glass or a crystalline 
groundmass, we can find an explanation of their origin in segre- 
gation or more perfect crystallization during the intratellurie phase 
of the magma, which has produced the enclosing volcanic rock. The 
xenoliths into which glass veins have penetrated from the enclosing 
hypersthene augite andesite, may be completely solidified rocks that 
were carried along by the rising magma. 
However, a great many of these xenoliths contain amphibole, a 
mineral which, as a rule, does not occur either unmodified or resorbed 
1) Cf. also H. KorPerBera, |. c., p. 270. 
