PETROGRAPHY. 71 
Biotite. Phenocrysts: about 3 per cent, not always present, 0.2 to 20 mm., anhedral, 
thick tabular, brown, usually much altered. 
Olivine. Groundmass: about i per cent, not always present, 0.03 to 0.2 mm., anhedral, 
equant. 
Nephelite. Groundmass: about 3 percent, not always present, formless, interstitial cement. 
Magnetite. Groundmass: about 4 per cent, o.oi to 0.03 mm., anhedral, equant. 
Apatite. Groundmass: about i per cent, o.oi to 0.04 mm., anhedral, prismatic. 
Chemical composition and norm as on p. 67. 
Type specimens from Bagnorea, Vulsinian District, and Monte Venere, Ciminian District. 
II. 6-5. 2. 2. Martina! Vicose=Ciminose [Leucite-Tephrite, San Martino Type]. 
Megascopic characters. This type is rather light gray and resembles the bagn- 
oreal ciminose. It is, however, much more highly porphyritic, phenocrysts of 
leucite and augite being abundant, though somewhat smaller than in the preceding 
type. Those of leucite are seldom over i mm. in diameter and are very incon- 
spicuous, while those of augite, in black prisms from i to 2 mm. long, are much 
more so. The groundmass is a rather dark gray, dense, and aphanitic. 
Microscopic characters. In thin section the leucite phenocrysts are seen to be 
either subhedral or sometimes quite anhedral, from 0.5 to i mm., in diameter. They 
carry few inclusions, which consist of minute dusty grains, generally gathered toward 
the center. The subhedral augite prismoids are somewhat more abundant, are 
much cracked and fragmentary, though mostly with crystal planes remaining, and 
are either colorless or of an almost imperceptible greenish tinge. They contain no 
inclusions. These two minerals constitute the only phenocrysts, none of feldspar 
or biotite having been observed. The leucite phenocrysts commonly occur in 
clusters of several individuals. 
The groundmass is somewhat indefinite and difficult of exact study. There 
are numerous small, colorless augite anhedra, which are either prismatic, equant, 
or irregular, and some small grains of magnetite, but none of the interstitial biotite 
seen in the previous type. These minerals are embedded in a colorless mass, 
which the crossed nicols resolve into very small, round anhedra of leucite, present 
in large numbers, indefinitely outlined prismoids of feldspar, which frequently show 
multiple twinning, though the grays are light and the structure is best seen with the 
aid of the selenite plate. Along with these are small flakes and indefinite interstitial 
areas of a colorless, feebly birefringent substance, which, however, does not seem 
to be nephelite, judging from the colors shown with the selenite plate, but is rather 
to be referred to one of the feldspars, probably orthoclase. No glass could be iden- 
tified with certainty. 
Chemical composition. One analysis, hitherto unpublished, was made of this 
type. In its lower silica and alumina, as well as in its somewhat higher bivalent 
oxides, this analysis differs very considerably from those of the other ones of ciminose 
rocks. The explanation lies in the fact that, while this rock is well within the 
borders of the class, rang, and subrang, it lies close to the border of the lendofelic 
order. So close, indeed, is it that the type may be regarded as transitional 
