1236 
The xenoliths mentioned sub 1 (Plate fig. 1 and 2) are first of all 
characterized by plagioclases, which ave distinguished from those of 
the phenoerysts of the enclosing rocks by the almost total absence 
of the frequent alternation of more basic and more acid zones. The 
crystals, often zonary and with a broad basic central part are chiefly 
composed of basic bytownite, the marginal zone is more acid. 
The amphibole is strongly pleochroitic, from a brownish red to 
light-yellow, and invariably shows a resorption-rim, often only narrow 
in many xenoliths and sometimes entirely absent where the crystals 
are contiguous to plagioclase, while it is often well developed where 
the amphibole is in contact with the glass-rich mass with microlites. 
These narrow resorption rims are composed of a black mass of ore. 
It is obvious that in part the amphibole has erystallized later than 
the plagioclases, which form idiomorphous crystals and then guard 
against resorption that portion of the amphibole with which they 
are in contact. In the xenoliths with more strongly resorbed amphi- 
bole, there occur entirely resorbed crystals, which can only be 
recognized as original amphibole by their crystalform. In the erystals 
that are partly unaltered, the resorption-rim consists only of a mass 
of ore or a marginal zone of ore, separated from the intact part of 
the crystal by an irregularly shaped pyroxene-rich zone, which is 
sometimes lacking and which sometimes occurs mixed with un- 
modified amphibole. Out of the resorption rims larger crystals of 
ore do not occur in the xenoliths. 
Some of the xenoliths with strongly resorbed amphiboles present 
a porphyric structure, the groundmass, which contains large, more 
or less idiomorphous amphibole crystals, consisting of plagioclase. 
Between these smaller plagioclase crystals, as in the non-porphyric 
xenoliths with larger plagioclases, more or less devitrified glass is 
found. Plagioclase-microlites and ore-skeletons are easy to distinguish 
in this mass; only a small number of pyroxene microlites’ are 
distinguishable; the devitrification is sometimes complete. 
The limit between the xenoliths and the enclosing lava is always 
such that the lava has adapted itself to the shapes of the xenolith. 
The erystal faces of the plagioclases and amphiboles have reached 
full development at the margin of the xenoliths so that the boundary 
line with the lava proceeds irregularly. Also the enclasped glassy 
mass shows that the minerals had not been perfectly crystallized, 
when the xenoliths were taken up in the enclosing magma, so they 
were still molten to a certain extent and may therefore be considered 
as an almost perfectly crystallized crust on the magma, which was 
effused from a larger depth and has produced the dome. The 
