480 ANNALS NEW YORK ACADEMY OF SCIENCES 



The data used do not claim to be exhaustive, and the results are advanced as 

 suggestive, rather than conclusive. 



This paper was illustrated with diagrams. 



Dr. Washington said in abstract: The island of Pantelleria is entirely 

 volcanic in origin. Its geologic structure has been variously interpreted, 

 and the views of the speaker differ in some important respects from those 

 of other observers, notably Foerstner and Bergeat. There is supposed to 

 have been formed first a large volcano, covering practically the whole area 

 and submarine in its first stages. This was composed of rather siliceous 

 soda-trachytes and later green pantellerites. The central and upper parts 

 of this cone disappeared, probably by explosion, in analogy with the history 

 of many other volcanoes, leaving a large central caldera, surrounded by an 

 encircling somma with steep inner scarps and gentle outer slopes. Within 

 the caldera arose the cone of the second period, now represented by Montagna 

 Grande, the summit of which is the culminating point of the island, and 

 Monte Gibele on the southeast. The lava of these is a very uniform soda- 

 trachyte. The crater of Monte Gibele seems to have been the original 

 eruptive center for the joint mass, but later the block of IMontagna Grande 

 was separated from the Gibele cone by a fault, with considerable tilting of 

 the fault block. On the western and northern sides of this block there were 

 formed several small parisitic cones, which gave vent to flows of black, 

 glassy pantellerlte. These and the trachytic flows of the Gibele volcano 

 nearly filled the whole floor of the original caldera, the only portion left 

 uncovered being a small elliptical lake, which is thus regarded as a residuum 

 of the old caldera floor and not an eruptive center. The next phase of 

 eruptive activity was confined to the northwestern part of the island, and the 

 lavas are entirely feldspar-basalts, forming several small cinder cones, with 

 flows of scoriaceous basalt. Eruptive activity on the island proper seems 

 to have ceased and is now evident only in some fumaroles and hot springs. 

 The rocks show a wide range in chemical composition, but belong to but 

 few distinct types. They are characterized by high soda, giving rise to the 

 presence of abundant soda-microcline, segirite, and the triclinic cossyrite 

 among the more salic types, and by the high amount of titanium among the 

 basalts. 



The paper was based on a visit made in 1905 and was illustrated with 

 lantern slides. 



After the reading of the papers, there were a few general remarks by 

 Professor Kemp and others, and arrangements were made for a field excur- 

 sion to the "trap" sheets of New Jersey. 



The Section then adjourned. 



Charles P. Berkey, 



Secreiary. 



