PETROGRAPHY. 79 
black. Olivine phenocrysts not always present, few, small, yellow. Groundmass: gray, 
aphanitic. 
Microscopic characters. Holocrystalline to percrystalline, magnophyric, dopatic. Pheno- 
crysts : about 20 per cent, orthoclase, andesine-labradorite, augite, biotite or olivine sometimes. 
Groundmass: about 80 per cent, either holocrystalline or with a very little glass, trachytic 
fabric, orthoclase, andesine-labradorite, augite, leucite (sometimes), nephelite (sometimes), 
magnetite, apatite, glass (sometimes). 
Orthoclase, OrjAb, to Or 4 Ab 3 . Phenocrysts: about 10 per cent, i to 20 mm., euhedral 
to subhedral, stout prismatic, Carlsbad twinning, inclusions rare. Groundmass: about 40 per 
cent, 0.05 to o.io mm., anhedral, prismatic, sometimes branched, with diverse to subparallel 
arrangement. 
Andesine-labradorite, Ab 3 An 4 to Ab 4 An 3 . Phenocrysts: about 5 per cent, 5 to 2omm. 
subhedral, stout prismatic, usually twinned, inclusions rare. Groundmass: about 15 per cent, 
0.05 to o. 10 mm., anhedral, prismatic, arrangement diverse to subparallel. 
Leucite. Phenocrysts none. Groundmass; not always present, sometimes about 2 per 
cent, 0.05 to o.io mm., anhedral round equant, faintly birefringent, some inclusions of augite 
microlites centrally arranged. 
Nephelite. Groundmass: not always present, up to about 8 per cent, anhedral, as cement 
interstitial between the feldspars. 
Augite. Phenocrysts: about 3 per cent, 0.5 to 2.0 mm., subhedral to anhedral, stout 
prismatic and fragmentary, gray or very pale greenish-yellow, few inclusions. Groundmass: 
about 10 per cent, 0.02 to 0.20 mm., anhedral, prismatic, colorless or very pale yellowish. 
Biotite. Phenocrysts: not always present, sometimes about 2 per cent, i to 3 mm., anhe- 
dral, thick tabular, much altered to granular aggregate. 
Olivine. Phenocrysts: not always present, sometimes about 2 per cent, i to 2 mm., sub- 
hedral to anhedral, fusiform to equant, colorless and usually fresh. 
Magnetite. Groundmass: about 3 per cent, o.oi to 0.03 mm., anhedral, equant. 
Apatite. Groundmass: about i per cent, 0.02 to 0.05 mm., subhedral, prismatic. 
Glass. Groundmass: not always present, about 5 per cent, usually colorless, sometimes 
brown, dusty with minute microlites. 
Chemical composition and norm as on p. 75 
Type specimens from Poggio Cavaliere, south shore of Lake Vico, Ciminian District, and 
from L'Arso, Ischia, Campanian District. 
II. 5. 2-3. 2. Foglianal Ciminose-Auruncose [Leucite-Tephrite, Viterbo Type]. 
Megascopic characters. This type much resembles in the hand specimen the 
viterbal vulsinose and ciminose already described, though the only known example 
differs texturally in being somewhat smaller in grain, both as to phenocrysts and 
groundmass. The rock is a leucite melaphyre, leucite phenocrysts, which vary in 
diameter from i to 5 mm. and which are usually euhedral, constituting about one- 
fifth of the rock volume. There are much less abundant phenocrysts of feldspar 
and augite, but on account of their small dimensions these are very inconspicuous. 
The groundmass is rather dark gray and aphanitic. The only specimen obtained 
is somewhat vesicular. 
Microscopic characters. In thin section the leucite phenocrysts present no 
remarkable features. They are euhedral, sometimes clustered, with very faint double 
refraction, and carry few inclusions, mostly small round dots of glass and usually 
