PETROGRAPHY. in 
The type has been uniformly called leucitite by petrographers, and the name is 
justifiable in the prevalent systems, on acccount of the small amount and inconspicu- 
ousness of the feldspars, though the presence of these in the Galera rock, and its 
consequent relation to the leucite-tephrites, is noted by Rosenbusch. 
QALERAL BRACCIANOSB. II. 7. 2. 2. 
Megascopic characters. Very dark gray or black, compact, aphyric, or very slightly 
porphyritic. Leucite phenocrysts rare, i to 5 mm., euhedral, equant, white, quite conspicuous. 
Augite phenocrysts very rare, i to 3 mm., prismatic, black. Groundmass, very dark gray or 
black, aphanitic, not vitreous. 
Microscopic characters. Holocrystalline to percrystalline, microporphyritic. Megapheno- 
crysts, none to 5 per cent, leucite, augite. Microphenocrysts, about 50 per cent, leucite, augite. 
Microgroundmass, about 50 per cent, augite, labradorite, nephelite (not always present), ortho- 
clase, magnetite, apatite, glass (not always present). Groundmass has clathrate fabric. 
Orthoclase, OrjAb^ Groundmass: 5 to o per cent, anhedral, interstitial, distinguishable 
with difficulty. 
Labradorite, Ab 2 An 3 . Groundmass: about 10 per cent, anhedral, to a small part tabular, 
mostly anhedral, interstitial patches. 
Leucite. Megaphenocrysts: 2 to o per cent, i to 5 mm., euhedral, equant, sometimes 
fragmentary, inclusions few. Microphenocrysts: about 35 per cent, o.i to 0.4 mm., anhedral 
equant, more or less circular sections, often skeleton forms, inclusions few to common, regularly 
arranged. 
Nephelite. Groundmass: about 6 per cent, anhedral, interstitial cement. 
Augite. Megaphenocrysts: 2 to o per cent, i to 3 mm., subhedral, prismatic, often frag- 
mentary, greenish-gray. Microphenocrysts: about 10 per cent, o.i to 0.3 mm., anhedral, 
prismatic, greenish-gray. Microgroundmass: about 20 per cent, 0.02 to o.iomm., anhedral, 
prismatic to equant, pale greenish-gray, arrangement partly diverse, partly tangential, around 
the leucite microphenocrysts. 
Magnetite. Groundmass : about 5 per cent, 0.02 to o . 05 mm., anhedral, equant. 
Apatite. Groundmass: about i per cent, 0.05 to o.iomm., subhedral, prismatic. 
Glass. 5 to o per cent, colorless to pale brown, usually absent. 
Chemical composition and norm as on p. 109. 
Type specimens from Crocicchie, south of Lake Bracciano, Sabatinian District. 
II. 7. 2. 2. Hernical Braccianose [Leucitite, Hernici TypeJ. 
Megascopic characters. Rocks of this type are dense, very dark gray or almost 
black, and either very fine-grained or quite aphanitic, but without glassy luster. They 
are typically aphyric, phenocrysts being either wholly wanting, or in some cases with 
small and rare ones of augite and leucite, which never form more than i or 2 per 
cent of the total volume. Vesicular forms may occur, but most of the specimens 
are perfectly compact. In the field they would be called typical basalts. 
Microscopic characters. Under the microscope the rock is seen to be com- 
posed predominantly of leucite and augite, with a little feldspar and accessory mag- 
netite and apatite. The texture, different from the clathrate one with numerous 
leucite microphenocrysts of the galeral type, is a xenomorphic granular one. 
Neither the leucite nor the augite are definitely phenocrystic, nor do either of them 
show much tendency to automorphic development, but of the two the augite is the 
more automorphic and has a greater tendency to form phenocrysts. Textures 
