PETROGRAPHY. 73 
Orthoclase, Or r Ab r 5.4 
Andesine, Ab 4 An 3 23.2 
Leucite 31.5 
Augite 33 . 8 
Magnetite 5.5 
Apatite 0.6 
From the above it will be seen that about 21 per cent of leucite is in the ground- 
mass, the rest of the salic portion of this being of feldspars, altogether amounting 
to about 31 per cent. The calculated and measured amounts of augite and mag- 
netite agree well, though the measured amount of the former is slightly lower than 
the calculated, the reverse being true of the ores. As compared with the norm, 
the only notable difference lies in the modal presence of leucite, replacing part of 
the orthoclase, and the total absence of nephelite. The type may then be called a 
leucite-alfersalphyro-ciminose. 
Occurrence. This type, so far as known, is found only in the neighborhood of 
San Martino, on the northwestern slope of the Vico Volcano in the Ciminian District, 
the best locality being at a quarry near the bridge over the Fosso della Parchetta. 
Rocks of the same type were also obtained behind the church of San Martino, above 
the town, and as blocks at the Ponte di Cetti, on the Via Aurelia, about 7 km. south- 
west of Viterbo, these last being somewhat decomposed. 
Name. The type name is derived from the locality where the type occurs. 
In the prevailing systems of classification this type would be regarded as a 
leucite-tephrite, on account of the very considerable amount of plagioclase and 
the small quantity of orthoclase. 
MARTINAL VICOSE-CIMINOSE. II. 6-5. 2. 2. 
Megascopic characters. Light gray, compact, highly porphyritic. Leucite phenocrysts 
abundant, but very small and inconspicuous. Augite phenocrysts abundant, small, prismatic, 
black. Groundmass light gray and aphanitic. 
Microscopic characters. Holocrystalline, mediophyric, dopatic. Phenocrysts: about 25 per 
cent, leucite, augite. Groundmass: about 75 per cent, somewhat felted fabric, andesine, leucite, 
augite, orthoclase, magnetite, apatite. 
Orthoclase, OrjAbj. Phenocrysts none. Groundmass: about 5 per cent, 0.05 to o.io mm., 
anhedral, prismatic and equant, also interstitial between the other constituents. 
Andesine, Ab 4 An 3 . Phenocrysts none. Groundmass: about 23 per cent, 0.05 to o.io 
mm., anhedral, prismatic, outlines rather indefinite, twinned, arrangement diverse. 
Leucite. Phenocrysts: about n per cent, 0.4 to i.o mm., subhedral, equant, often clus- 
tered, few dusty inclusions. Groundmass: about 20 per cent, 0.02 to 0.05 mm., anhedral, 
equant, free from inclusions, often difficult to distinguish from the groundmass orthoclase. 
Augite. Phenocrysts: about 12 per cent, 0.5 to 2.0 mm., subhedral, prismatic, fusiform 
and fragmentary, colorless, no inclusions. Groundmass: about 20 per cent, 0.02 to 0.05 mm., 
anhedral, prismatic, equant or irregular, colorless. 
Magnetite. Groundmass: about 4 per cent, 0.02 to 0.04 mm., anhedral, equant. 
Chemical composition and norm as on p. 72. 
Type specimen from Fosso della Parchetta, San Martino, Vico Volcano, Ciminian District. 
