96 THE ROMAN COMAGMATIC REGION. 
II. 6. 2. 2. Bagnoreal Vicose [Leiicite-Tephrite, Bagnorea Type] . 
Megascopic characters. In the hand specimen these rocks closely resemble 
the bagnoreal ciminose already described. They are medium gray, varying some- 
what in different specimens, but never becoming very light or very dark. While 
distinctly porphyritic, phenocrysts are few and inconspicuous. These are mostly 
of leucite, in subhedral crystals, from 3 to 10 mm. in diameter, usually of a very 
pale-gray color, often with a slightly yellowish tinge. Small prismatic phenocrysts 
of black augite are still more rare. In some specimens are one or two rounded 
patches (up to 5 cm. in diameter), of medium-grained aggregates of small leucite 
and augite grains, apparently early solidified segregations from the magma (enclaves 
homceo genes'). The groundmass is distinctly phanerocrystalline and fine-grained, 
the separate particles of light and dark minerals clearly visible to the naked eye. 
Microscopic characters. Studied in thin section the rare leucite phenocrysts 
show more or less irregular outlines, the crystal form not having been well developed. 
The double refraction and twinning are strongly marked, and inclusions are not 
common. The subhedrally prismatic augite phenocrysts are of the usual pale-gray 
color, though in some specimens there is a tendency to zonal growth, as shown by a 
slight deepening of the greenish tint toward the center or by progressive extinctions. 
The groundmass is holocrystalline in nearly all the specimens examined, the 
fabric is intersertal, and it is composed in great part of leucite, partly in the form of 
small, subhedral spheroids, and partly in quite irregular anhedra. All these are 
clear and carry few if any inclusions. With these leucites are many small feldspar 
laths, the majority being of a twinned labradorite about Ab 2 An 3 , with fewer of 
alkali-feldspar, which is also present to some extent as an interstitial cement in 
patches. The arrangement of these feldspar laths is diverse, producing an intersertal 
fabric. Small augites are also abundant in stout subhedral prismoids, often so short 
as to be almost equant. The gray color of this is also slightly more greenish than 
is usually true of the rocks of the region, though the absence of pleochroism indicates 
that it does not carry any of the aegirite molecule. Small magnetite grains and 
apatite prisms are present, both in rather greater amount than is usually the case 
in similar rocks elsewhere in the region, but no olivine could be detected. In some 
of the specimens there is some colorless nephelite as an interstitial base, the last 
product of solidification, while in a few this is partly replaced by a colorless glass, the 
amount of which, however, is never great. 
Chemical composition. Of this type two hitherto unpublished analyses are given. 
In III is found an earlier analysis of the same specimen as that used for II, in which 
MgO was determined from loss, and with no determinations of TiO 2 and P 2 O S . 
As this was unsatisfactory, all the main constituents from silica to lime were rede- 
termined on another portion of the specimen, the determinations of the alkalis being 
accepted as correct; and these, with the additional determinations of the minor 
constituents, form the analysis in II. 
