PETROGRAPHY. 123 
Name. The subrang name is derived from that of Mount Vesuvius, on the 
basis of the position formerly* assigned the types of vesbal and scalal braccianose. 
But, as we have seen above,f these rocks do not properly fall in vesuvose (II. 8. 
2. 2), but in braccianose (II. 7. 2. 2). The error is an unfortunate one and the 
subrang II. 7. 2. 2 could appropriately be called vesuvose, as this subrang is very 
abundant and characteristic at Vesuvius. But on the grounds of priority and 
previous publication, and on account of the liability to misunderstanding if a 
change is made, it is deemed best to preserve the names with their original signifi- 
cations as to rang and subrang. The type name will be discussed later, 
In the prevailing systems of classification this type would be included among 
the leucitites, consisting, as the rocks do almost exclusively, of leucite and augite. 
III. 8-7. 2. 2. Galeral Albanose-Jugose [Leucitite, Galera Type]. 
Megascopic characters. In the hand specimen this type can not be distin- 
guished from galeral braccianose, vesuvose, or albanose. The rock is very dark 
gray or black, with rare phenocrysts of leucite or augite in the aphanitic or very fine- 
grained groundmass, and is typically a basalt, or a melaphyre if the few phenocrysts 
are considered to be of importance. Vesicular forms seem to be uncommon, and 
all my specimens are very compact. 
Microscopic characters. In thin section likewise it is a matter of great difficulty, 
if not an impossibility in some cases, to discriminate between this type and those 
mentioned above. But in general the greater amount of augite serves to distinguish 
them from the braccianose and the presence of small amounts of feldspar from the 
albanose. 
In the type specimens the leucite phenocrysts are rarely seen in the section and 
call for no description. Those of augite are more numerous, from 0.5 to i.o mm. 
long, stoutly prismatic and subhedral, and of the usual very pale -gray color, almost 
wholly without inclusions. The microgroundmass shows a clathrate fabric, with 
abundant small round leucite anhedra, weakly birefringent, between which lie 
many small prismoids and grains of common augite. In the type specimen the 
tangential arrangement of the prisms is not so well marked as in the galeral brac- 
cianose from Crocicchie, and the small augites are rather more often in the form of 
equant grains, showing a transition toward the hernical type, but the characteristic 
round leucites indicate that the fabric may still be called clathrate. There are 
many small and irregular grains of magnetite and some olivine grains and apatite 
needles. Between these small crystals is a colorless base, in part isotropic, but the 
greater part of this is doubly refracting, with an index of refraction and birefringence 
decidedly greater than leucite, and apparently greater also than nephelite. Though 
this shows no twinning lamellae it may be regarded as feldspar, mostly plagioclase, 
which the calculated norm shows to be present, and as treatment of the rock powder 
with dilute acid furnished only very small amounts of gelatinous silica. In some of 
* Washington, Prof. Paper U. S. Geol. Surv. No. 14, 1003, p. 307. 
t Cf. pp. 104 and no. 
