94 RIO GRANDE COAL FIELDS OF TEXAS. [bull. 164. 
nite (Table III) it will be noticed that the latter rock differs essentially, 
containing a larger amount of silica and a smaller amount of iron. This 
chemical variation is manifested mineralogically by a greater develop- 
ment of free silica and by a total absence of ferromagnesian constit- 
uents in the groundmass of the rock. 1 
The geological occurrence of the paisanite 2 in the characteristic dike 
form is in marked contrast to the typical effusive character of the 
pantellerite. 
The distribution of pantellerite outside of Texas is limited to the 
island of Pantelleria, although similar lava types are found on some 
of the volcanic islands off the coast of Africa, as well as on the 
mainland itself. 
Pantelleria is situated about 70 miles southwest of Sicily, nearly 
midway between that island and Africa. It was visited in 1829 by 
Gemmellaro, who described from there a peculiar, greenish-gray 
rock type as "lave trachitichi moderne." 3 
In 1881 Foerstner named this lava pantellerite, and characterized it 
as a young, effusive rock, rich in iron, and containing a hornblendic 
mineral, called by him cossyriteS In a later paper 5 he says that the 
rock shows sometimes a trachytic, often a vitreous obsidian, habit, 
and that it covers an area of 40 to 60 square kilometers, or the major 
part of the island. Forty-five volcanic centers and fifty flows sur- 
round an andesite core. Besides the latter rock, the pantellerite was 
associated with phonolite, feldspar, basalt, and rhyolite. 
It has already been shown that in the Vieja Mountains the two lat- 
ter rock types accompany the pantellerite. Phonolite and andesite 
from the Davis Mountains, 30 to 70 miles east of the Vieja Range, have 
been described by Osann. 6 This similarity in the mineral composition, 
as well as the geological associations of these younger rocks with the 
lavas from Pantelleria, renders the discovery in Texas of a similar cir- 
cumscribed area of eruption a matter of great interest. 
The following are some of the more important occurrences of 
younger rock types resembling pantellerite in their mineral composi- 
tion: 
(1) Acmite-trachyte from the islands of San Miguel and Fayal, of 
the Azores, and from the island of Terceira; 7 also from the neighbor- 
hood of Naiwaseha Lake and from the Kaiwangaine Valley, northeast 
of Kilimandscharo Massif, East Africa. 8 
1 Osann, op. cit., p. 438. 
2 Ibid., pp. 404,405. 
3 C. Gemmellaro, Sopra 1' isola vulcanica di Pantelleria: Atti dell' Accad. Gioenia, Vol. V, 1829. 
4 H. Foerstner, Nota preliminare sulla geologia dell' isola di Pantelleria: Roma, Tipogr. Barbea, 
1881, p. 15. 
&Ueber Cossyrite: Zeitsch. fur Krystallog., Vol. V, 1881, pp. 348-349. 
6 Osann, op. cit., p. 126. 
7 0. Miigge, Petrog. Untersuchung. an Gesteinen von den Azoren: Neues Jahrb. fur Min., Vol. II, 
1883, pp. 212-218. 
b O. Miigge, Ueber einige Gesteine des Massai-Landes: Neues Jahrb. fur Min., Vol. IV, 1886, p. 591. 
