PETROGRAPHY. 57 
Mode. As the mode is indeterminate, through the presence of abundant glass, 
discussion of it is uncalled for. Were the rock holocrystalline, however, with the 
same minerals present as shown in this form, its mode would probably be roughly 
something like this: 
Quartz 14 
Orthoclase, Or 4 Ab 3 37 
Labradorite, Abj An 2 25 
Biotite 13 
Augite and hypersthene 6 
Ores 5 
Occurrence. Sorianal harzose was found only in the Ciminian District, around 
the Cimino Volcano, where the lava form occurs as flows and as blocks in the tuffs 
at many places. Among the localities where I obtained typical specimens may be 
mentioned flows from Monte Ciliano, along the highway northwest of Soriano, and 
at Le Piaggie, about 3 km. southwest of Soriano, as well as in the ravine near Bag- 
naia, where it occurs as blocks (sometimes reddened through weathering) in the 
lower tuffs. 
The breccia form of sorianal harzose (peperino) is met with in abundance 
around the Cimino Volcano, especially on the west, north, and northeast, and it 
forms much of the lower slopes of the hills. So abundant is it that enumeration of 
special localities is superfluous, and the only ones that need be named are the quarry 
of L. Mercati, at La Cava, near Viterbo, from which the analyzed specimen was 
obtained, and the vicinity of Bagnaia. 
Name. The derivation of the subrang name has been discussed elsewhere. 
That of the type is derived from the town of Soriano, near which it is very abundant. 
In prevailing classifications there has been considerable diversity as to the 
name of these rocks. The lava form has been called a trachyte by vom Rath, an 
andesitic trachyte or trachy-andesite by Mercalli, and a mica-andesite by Deecke. 
Consideration of the mode, which shows almost equal amounts of alkali and soda- 
lime feldspar, would seem to render Ransome's term "latite" suitable, especially as 
the free silica has not crystallized out as quartz. As the prominent alferric mineral 
is biotite it may be classed, then, as biotite-latite. 
The diversity of opinion as to the origin of the breccia form has already been 
touched on. The rocks known locally as peperiiw, and called by Brocchi necrolite, 
on account of their use by the Etruscans for sarcophagi, embrace two distinct types. 
The one is the peperite des hauteurs of Sabatini and the trachite-andesitico a grossi 
sanidini of Mercalli, which is the earliest product of eruption and forms the nucleus 
of the Cimino Volcano. This peperino apparently belongs to the subrang vulsinose 
and is sometimes a lava, sometimes a flow-breccia, and sometimes a tuff. The other 
is the peperite ty pique of Sabatini and the trachite-andesitico a piccoli felspati of 
Mercalli, which overlies the other, and which is apparently earlier than the flows of 
ciminose to be described presently. This peperino is the breccia form of sorianal 
harzose, and might be called in the prevailing nomenclature a biotite-latite breccia. 
