82 THE ROMAN COMAGMATIC REGION. 
In the prevailing systems of classification the rocks of this type would best be 
called leucite-tephrite, on account of the preponderance of labradorite over ortho- 
clase among the phenocrysts, as well as because there is somewhat more soda-lime 
feldspar than alkali feldspar in the mode. 
FOQLIANAL CIMINOSE-AURUNCOSE. II. 5. 2-3. 2. 
Megascopic characters. Dark gray, sprinkled with numerous white phenocrysts of leucite. 
Leucite phenocrysts very abundant, i to 5 mm., white, euhedral, conspicuous. Feldspar pheno- 
crysts very few, small, inconspicuous. Augite phenocrysts few, prismatic, black, inconspicu- 
ous. Groundmass dark gray, aphanitic. 
Microscopic characters. Holocrystalline, mediophyric, dopatic. Phenocrysts: about 30 per 
cent, leucite, labradorite, orthoclase, augite. Groundmass : about 70 per cent, andesine, ortho- 
clase, augite, leucite, olivine, magnetite, apatite. Fabric felted or hyalopilitic ( ?). 
Orthoclase, OrjAb^ Phenocrysts: about 2 per cent, 0.5 to i.o mm., subhedral, stout 
prismatic, inclusions rare. Groundmass: about 20 per cent, part anhedral prismatic, o.oi to 
0.05 mm., part as interstitial cement. 
Andesine, AbjAn x . Groundmass: about 30 per cent, 0.02 to 0.05 mm., anhedral, part 
thin prismatic, part apparently as interstitial cement. 
Labradorite, AbjA^. Phenocrysts: about 7 per cent, 0.5 to 2.0 mm., euhedral, stout 
prismatic, twinned, inclusions rare. 
Leucite. Phenocrysts: about 20 per cent, i to 5 mm., euhedral to subhedral, equant trape- 
zohedra, often clustered, inclusions few. Groundmass: about 5 per cent, 0.02 to 0.05 mm., 
anhedral, equant, inclusions few. 
Augite. Phenocrysts: about i per cent, 0.5 to i.o mm., subhedral, stout prismatic, pale 
greenish yellow, nonpleochroic. Groundmass: about 8 per cent, 0.005 to 0.02 mm., anhedral, 
prismatic and equant, colorless. 
Olivine. Groundmass: about 2 per cent, o.i to 0.5 mm., subhedral, stout prismatic to 
equant, colorless. 
Magnetite. Groundmass: about 4 per cent, 0.005 t o.oi mm., anhedral, equant. 
Class. Groundmass : a very little may be present, but is not easily recognized. 
Chemical composition and norm as on p. 80. 
Type specimen from Croce di San Martino, Vico Volcano, Ciminian District. 
II. 5. 2-3. 2. Teanal Ciminose-Auruncose [Leucite-Trachyte, Teano Type]. 
Megascopic characters. Rocks of this type are rather light gray and porphy- 
ritic, the phenocrysts of leucite, biotite, and augite being small and not very abundant. 
The grayish leucite phenocrysts vary from i to 5 mm. in diameter, are sub- 
hedral to anhedral, and not very conspicuous. Those of the alferric minerals are 
smaller, seldom over 2 mm. in length, and black, the biotite in thin tables and the 
pyroxene in slender prisms. The compact, medium gray groundmass is aphanitic. 
In the field these rocks would be called biotite-leucite-leucophyres. 
Microscopic characters. In thin section the following minerals are seen to be 
present: Alkali feldspar, soda-lime feldspar, leucite, augite, biotite, ores, and apatite. 
The two feldspars are present in about equal amount and together make up about 
half the rock. As subhedral, stout prismoidal phenocrysts they are rare, being 
for the most part in the groundmass as anhedral patches and small laths, the former 
mostly of the alkali, and the latter of the soda-lime feldspar, though it is not always 
possible to distinguish clearly between them, except by the refractive indices, on 
