126 THE ROMAN COMAGMATIC REGION. 
Augite. Microphenocrysts: about 15 per cent, o. 10 to 0.50 mm., anhedral to subhedral, 
prismatic and fragmentary, pale greenish-gray, often zonal, inclusions few. Groundmass: 
about 30 per cent, 0.02 to o.iomm., anhedral, prismatic to equant, very pale greenish-gray, 
arrangement somewhat tangential around the leucites. 
Olivi'ne. Groundmass: about 4 per cent, 0.05 to o. 10, anhedral, equant, colorless. 
Magnetite. About 2 per cent, o.oi to 0.05 mm., anhedral, equant. 
Apatite. About i per cent, 0.02 to 0.05 mm., subhedral, prismatic. 
Chemical composition and norm as on p. 124. 
Type specimen from Monte Jugo, Vulsinian District. 
III. 7. 3. 2. Fiordinal Fiasconose [Leucite-Basanite, Fiordine Type]. 
Megascopic characters. This type is very dark gray and porphyritic. Abun- 
dant phenocrysts of dark-green or black augite, from 2 to 10 and even 20 mm. 
long, with fewer but still numerous phenocrysts of olive-green olivine, of about the 
same sizes, constitute some 30 per cent of the rock volume. The groundmass in 
which they lie is dark gray, compact, and quite aphanitic. The rock is dense and 
heavy, evidently highly femic, and in the field would go under the name of olivine- 
augite melaphyre. 
Microscopic characters. The very abundant augite phenocrysts are for the most 
part euhedral to subhedral, often "corroded" at the borders into small pits and 
pockets, and not uncommonly fragmentary. They are of the usual very pale-gray 
color, here without any tinge of green, and are remarkably free from inclusions, 
small grains of magnetite being the only ones observed. The large olivines are 
similarly euhedral to subhedral, often fragmentary, showing the common simple 
planes, quite colorless, as free from inclusions as the augites (here also magnetite 
being the only included mineral), and are quite fresh, except for a thin external dark 
brown zone. 
The groundmass in which these lie contains many small, equant anhedra of 
augite and euhedral crystals of olivine which run serially up to the phenocrysts in 
size. With them are considerable numbers of very small, round, water-clear leu- 
cites, in part subhedral with crystal planes and in part completely anhedral, the 
double refraction being weak but discernible with a selenite plate. There are also a 
few small, irregular areas of brownish biotite and some magnetite grains, but no 
feldspar laths or apatite. 
The colorless base between these crystals shows considerable diversity in dif- 
ferent parts of the section. In places it shows the birefringence and twinning 
lamellae of plagioclase, the extinction angles of which correspond to an almost pure 
anorthite. These feldspars form irregular areas inclosing poikilitically the smaller 
crystals, and with the small leucites standing out well against them on account of 
the considerably lower refractive index. Elsewhere the patches are more feebly 
birefringent and without twinning lamellae, and are regarded as nephelite, while again 
the base is isotropic, and is either nephelite in basal section or less commonly glass. 
Chemical composition. An analysis of the rock from near Fiordine was made, 
a large amount of material being taken to obtain a representative sample. For com- 
