PETROGRAPHY. 65 
ured in thin section. The small amount of normative hypersthene was assumed 
to belong to the augite molecule, though the orthorhombic pyroxene may actually 
exist among the small pyroxene prisms, since we find it in the sorianal harzose from 
the same volcano. The results of the calculation were as follows: 
Soda-orthoclase, Ori Ab 3 50. 7 
Labradorite, A^Arij J 3 i 
Augite 23 . 2 
Olivine 11.2 
Magnetite 0.9 
Apatite 0.9 
The calculation of the mode of the Colonetta rock was also simple. An 
amount of the normative hypersthene corresponding to that in the preceding case 
was assumed to enter into the augite molecule, while the balance was recalculated 
as olivine, the amount of which agrees fairly well with the appearance of the section. 
This calculation of olivine necessarily adds to the amount of free silica, which is 
stated as quartz, and which we must assume to be present in the glass base. In 
the case of both rocks the composition of the augite, apart from the hypersthene 
molecules, was assumed to be that of the Ticchiena augite referred to elsewhere. 
These readjustments give the following figures: 
Soda-orthoclase, Ore Ab t 43-6 
Labradorite, Ab, An 2 16. i 
Quartz 4.6 
Augite 22.4 
Olivine 11.7 
Magnetite o. 9 
Apatite 0.7 
It is evident that the two modes are essentially identical, the amount of quartz 
or glass being so small as to be negligible. Taking the presence of olivine into 
account the type may be described as normative olivinic salfemphyro-ciminose; for 
which the shorter term "fiescolal ciminose" is an advantageous substitute. 
The occurrence of quartz or a highly quaric glass along with olivine need not 
cause surprise, as a number of similar cases are well known. Indeed, from the 
generally observed easy solidification of highly quaric magmas or partial magmas 
before complete crystallization, the presence of glass in the specimen which shows 
some normative quartz, while that without this is holocrystalline, is readily intelligible. 
Occurrence. Rocks of this type are confined to the Ciminian District, so far 
as known. In this they are very abundant around the Cimino Volcano, and among 
representative localities may be mentioned the stream bed at Cavorcie, the quarry 
of the Chiesa dei Frati at Madonna della Quercia, a flow west of Villa Lante, flows 
and blocks in the tuffs at Monte Ciliano and near Soriano, and the type localities at 
La Colonetta and Fontana di Fiescoli. 
Name. The name of the subrang has been already explained as derived, like 
that formerly proposed for the group of trachytic rocks characterized by the presence 
