40 THE ROMAN COMAGMATIC REGION. 
The type may also occur in the Auruncan District. The analysis of a "leu- 
cite-trachyte " by vom Rath given in column IV is that of a vulsinose and with a 
leucitic mode. A rock with prominent leucite phenocrysts collected by me at this 
locality shows much less silica (51.20) and falls in vicose (II. 6. 2. 2), and is clearly 
not the same as vom Rath's rock, as his silica determination can not be so greatly in 
error. His description is not very clear or detailed, but it may be gathered that the 
mode is probably closely like that of the bagnoreal ciminose and vicose, to be 
described later, in which the leucite phenocrysts are much less abundant and less 
prominent, and with more numerous augite phenocrysts. I have therefore assigned 
vom Rath's rock provisionally to the type of bagnoreal vulsinose, though this needs 
further investigation. The descriptions of Bucca lead one to believe that true 
viterbal vulsinose is quite abundant in the Auruncan District, as at the localities 
of Valogno Piccolo and below Orchi. I did not visit the former locality, and the 
rocks which I collected near the latter village are not of this type. 
Name. The type adjective, viterbal, is derived from the city of Viterbo, the 
chief town of the Ciminian District. In prevailing classifications rocks of this 
type have gone under very different names. If we disregard the small amount of 
labradorite, which is always subordinate to the orthoclase, the rocks would be called 
by Zirkel leucite-trachytes, and by Rosenbusch leucite-phonolites. Of these two, 
that of Zirkel is the better, in my opinion, for reasons given elsewhere. Some 
petrographers, however, regard the presence of the labradorite as of more impor- 
tance than that of the more abundant orthoclase, and therefore call these rocks leucite- 
tephrites. Of this appellation it may be remarked that it is at variance with the 
quantitative relations of the two feldspars, ignoring that which is most abundant 
and laying special stress on the subordinate one. It may also be noted that these 
rocks differ widely from others of the region to which the name of leucite-tephrite 
is applied with as much logical reason as the prevailing systems are capable of. 
Under the prevailing systems, however, there is no means of distinguishing this 
well-marked type from others in which the leucite is not decidedly porphyritic. 
The characters are so well marked and so easily recognizable, and these rocks are 
so important in the petrography of the region, that they would seem to be deserving 
of a separate name. For this the term viterbite may be used. 
I. 5.2. 2. Pallanzanal Vulsinose [Leucite-Trachyte, Pallanzana Type]. 
This type is intermediate between the bolsenal and viterbal types. It resembles 
the former in the rather small and rare feldspar phenocrysts and the latter in the 
presence of phenocrysts of leucite, though these last are much smaller and far less 
abundant than in the rocks just described. 
The rocks are all more or less decomposed, being so friable that it was impos- 
sible to obtain good specimens, and it is noteworthy that all writers mention the 
uniformly altered condition. On this account no analysis was made of them, so 
that their exact magmatic position is not sure. Microscopic study, however, ren- 
