54 THE ROMAN COMAGMATIC REGION. 
position of this type, its peculiar mode or mineral composition, the abundance of 
haiiyne, and the very large size of the leucite phenocrysts distinguish it clearly from 
nearly all other leucite-phonolites, and in the prevailing classifications it would seem 
to be deserving of a distinct name, for which that of tavolatite might be chosen. 
TAVOLATAL JANE1ROSE-APPIANOSE. II-I. 7. I. 3. 
Megascopic characters. Light gray, compact, highly porphyritic. Leucite phenocrysts 
numerous, large, 10 to 30 mm., well crystallized, but often fragmentary, few inclusions. Hatiyne 
phenocrysts numerous but very small, up to i mm., blue. Augite phenocrysts few and small, 
black. Garnet phenocrysts very rare and small, yellow. Groundmass: light gray, phanero- 
crystalline, very fine-grained. 
Microscopic characters. Holocrystalline, porphyritic, dopatic. Megaphenocrysts : about 30 
per cent, leucite, haiiyne, aegirite-augite, garnet. Microphenocrysts : about 55 per cent, leucite, 
orthoclase, haiiyne, labradorite, aegirite-augite, garnet. Microgroundmass, about 15 per cent, 
nephelite, orthoclase ? 
Leucite. Megaphenocrysts: about 15 per cent, 10 to 30 mm., euhedral to subhedral, 
often fragmentary, equant, twinned, inclusions few, of haiiyne and augite. Microphenocrysts: 
about 20 per cent, o.i to 0.3 mm., anhedral, equant and irregular, often not well defined, few 
inclusions. 
Orthoclase. Microphenocrysts, about 20 per cent, 0.05 to 0.50 mm., anhedral to sub- 
hedral, stout prismatic, arrangement diverse. Microgroundmass: about 5 per cent possibly 
present as cement. 
Nephelite. Groundmass: about 12 per cent, interstitial cement. 
Haiiyne. Megaphenocrysts: about 8 per cent, 0.5 to i.omm., eahedral and anhedral, 
equant and irregular, often deeply corroded, usually blue, many dusty inclusions. Microphen- 
ocrysts: about 5 per cent, 0.05 to 0.5 mm., same characters as megaphenocrysts except size. 
Labradorite, Ab t A.n 2 . Phenocrysts: about 7 per cent, 0.05 to 0.50 mm., anhedral, stout 
prismatic, multiple twinning constant. 
JEgirite-augite. Megaphenocrysts: about 5 per cent; microphenocrysts: about 6 per 
cent; 0.05 to a.omm., anhedral to subhedral, stout prismatic, brownish-green, pleochroic. 
Garnet. Phenocrysts: about 2 per cent, 0.2 to 2.0 mm., subhedral, equant, brown, often 
zonal. 
Biotite. Phenocrysts: about i per cent, subhedral, tabular, brown. 
Chemical composition, norm, a.ad mode as above. 
Type specimen from Osteria di Tavolato, Via Appia Nuova, Latian District. 
II. 4. 3. 3. Sorianal Harzose [Biotite-Latite, Soriano Type]. 
The rocks of this type occur in the Roman Region in two distinct forms, the 
one a compact lava, the other a flow-breccia. Although the two seem, at first sight, 
to be quite distinct, they may both be considered to be of the same petrographic 
type, the differences between them being differences of consolidation merely, due 
to the viscosity of the material and slightly varying accidental conditions during 
extrusion. For this reason they will be considered together, though the field and 
microscopic characters of each will be described separately. 
Megascopic characters Lava form : These rocks are very dark, compact and 
highly porphyritic. Small tabular phenocrysts of feldspar are abundant, making 
up about one-quarter of the rock volume. With them are many, but less numer- 
ous, small, glistening, dark tables of biotite and prisms of pyroxene. These lie 
