THE VOLCANOES AND ROCKS OF PANTELLERIA 695 
Mode.—The groundmass is too fine grained, and the texture 
too confused, to permit of satisfactory measurements by Rosiwal’s 
method of the relative amounts of the constituent minerals, but a 
recalculation from the norm, taking the thin sections into considera- 
tion, yields the following mode for the Zeneti trachyte: 
(O) TERI 27 ao ae eg Ret eet ie 15 
SOM eMCLOCMNE s Ans. Risen A OY eae th en 63 
PNG RITELC “AN BITE is" Sid's avy aati sco ho hd Ge eae 12 
1 S(Grir21 DESIG Ce ete eens OR oa ae OPC rat Me ite) 
Too 
These trachytes are in many ways intermediate between the 
Gibelé trachytes and the pantellerites, so that the name of pan- 
telleritic trachyte is applicable to them. 
COMENDITE, NERA TYPE (NERAL GRORUDOSE) 
Occurrence—Flows of this rock—the ‘white liparite’’ of 
Foerstner—form sheets above those of the preceding type. They 
are met with at various points along the inner scarp of the caldera 
wall, notably at Cuddia Nera, where two superposed flows are 
seen, the upper being platy in structure and the lower distinctly 
columnar and the rather narrow columns often curved. They 
are capped by a thin sheet of the green pantellerite, next to be 
described. The type also occurs in the scarp of Costa Zichidi, 
on the west side of the Val di Monastero, and on the southeast 
side of the Valle Silhoumen, according to Forestner, though I did 
not see it here. Foerstner mentions it at the so-called Polveriera, 
the ancient citadel of Cossyra, southeast of the town, but probably 
terracing for vineyards has since covered the exposure as I observed 
here only basalts from the Sant’ Elmo flow. Along the steep 
parts of the coast flows of this rock are seen, occurrences being at 
Punta Pozzolana, Cala Cinque Denti, and Cala Porticello. At 
the first of these the rock is rather tuffaceous, is covered by a 
yellowish pantelleritic tuff, and overlies a flow and scoria bed of 
black and green pantellerite, while at the sea-level is the vitrophyric 
zenetal grorudose described above. This type is briefly described 
by Rosenbusch.* 
tH. Rosenbusch, of. cit., p. 830. 
