PETROGRAPHY. 
141 
Augite. About 25 per cent, 0.05 to 0.50 mm., subhedral to anhedral, partly in prismatic 
and equant, partly irregular and interstitial; pale gray, few inclusions. 
Olivine. About 7 per cent, 0.05 to o. 10 mm., anhedral, equant. 
Melilite. About 12 per cent, anhedral, interstitial patches, sometimes poikilitic about the 
smaller crystals, areas up to 2 mm. in diameter, "pflock" structure common, pale yellowish. 
Magnetite. About 4 per cent, 0.02 to 0.05 mm., anhedral, equant. 
Apatite. About i per cent, 0.03 to 0.08 mm., subhedral, prismatic. 
Chemical composition and norm as on p. 139. 
Type specimen from Capo di Bove, Latian District, 
Correlation of Types. 
As the types described in the preceding pages are numerous, and as the char- 
acteristics on which they are based differ in certain respects from those which 
obtain in the prevailing systems, it will be not amiss to point out briefly the chief 
features in which those of the quantitative system resemble or differ from each other, 
and also to indicate the correlation between them and those of the prevailing systems. 
TYPES OF THE QUANTITATIVE SYSTEM. 
In correlating the types from the point of view of the quantitative system alone 
we may devote special attention to the modal and textural characters denoted by 
the typal adjective, though the magmatic character, as expressed by the subrang 
name, must also be considered. It will have been noticed that the same type adjec- 
tive is applied to different subrangs. This has been the case when the subrangs 
resemble each other quite closely, as with vulsinose, pulaskose, and monzonose, or 
with vesuvose and albanose, and when the modal and textural characters of the 
representatives of the different subrangs are so much alike that very close study, 
especially from the chemical side, is necessary to distinguish between the rocks. 
Thus only a chemical analysis or careful optical measurements can distinguish 
between the three types of bolsenal vulsinose, pulaskose, and monzonose, the modal 
characters differing but slightly and the textural being practically identical. By 
this plan of a single type adjective applicable to several subrangs the great similarity 
between such types is made manifest and the number of new terms is lessened. 
From the modal and textural points of view types may resemble or differ from 
each other either in respect to mode, or to texture, or to both together, and they may 
also form series of types with members which are homologous modally or texturally. 
This is illustrated by the following examples: 
I. 5. 1. 3. 
I. 5. 2. 2. 
II. 5. 2. 2. 
II. 5. 2. 3. 
Ischial phlegrose. 
Cumal phlegrose. 
Arsal vulsinose. 
Bolsenal vulsinose. 
Arsal ciminose. 
Fiescolal ciminose. 
Arsal monzonose. 
Bolsenal monzonose. 
II. 5. 2. 2. 
II. 6.2. 2. 
II. 7.2.2. 
Viterbal ciminose. 
Bagnoreal ciminose. 
(Orvietal ciminose.) 
Foglianal vicose. 
Bagnoreal vicose. 
Orvietal vicose. 
Vesbal braccianose. 
Scalal braccianose. 
Galeral braccianose. 
