Reviews — H. S. Washington — Volcanoes of Pantelleria. 565 



XIII. — The Volcanoes and Rocks of Pantellekia. By Henry S. 

 Washington, Journal of Geology, vol. xxi, No. 7, p. 653, 

 No. 8, p. 683, 1913; vol. xxii, No. 1, p. 16, 1914. 



THE island of Pantelleria ' lies midway between Sicily and Tunis, 

 and with the exception of some local beds of travertine the 

 exposed rocks which enter into its architecture are wholly volcanic. 

 It is probable that a basement of plutonic rocks underlies the volcanic 

 superstructure, for fragments of granite have been found in the lavas 

 of Pantelleria, and xenoliths of diorite in the lava of Linosa, a small 

 volcanic island which lies to the south-east. Pantelleria lias become 

 classic through the researches of Foerstner, who discovered there 

 a remarkable series of lavas containing soda microclitie and cossyrite. 

 In 1905 a re-examination of the island was undertaken by 

 Dr. Washington, and the present paper is the outcome of his studies 

 ia the field and subsequently in the laboratory. 



The volcanic history of the island appears to have been as follows : — 

 Phase 1. — The building up of a large cone on a granite basement 

 by successive flows of — 



(1) Pantelleritic ti'achyte . . 66"85Si02. 



(2) Comendite .... 72-21 Si Og. 



(3) ^girite or green pantellerite . 71 "15 SiOg. 



This phase was ended by the formation of a caldera with its 

 surrounding somma, owing either to explosion or to subsidence. 



Phase 2. — The building up of a cone within the caldera by flows of — 



(4) Soda trachyte .... 63-46 Si Og. 



(5) Pantelleritic pumice . . . 67-32 Si Og. 

 Dislocation of part of the cone then took place, tilting up the south 



and depressing the north. Through the fractures so produced an 

 eruption then took place of — 



(6) Black pantellerite . . . 69-08 Si Oo. 

 Phase 3. — At the north-western end of the island eruptions of — 



(7) Basalt 46-09 SiOo 



then broke through. A submarine eruption in 1891 near the north- 

 western coast marks the last sign of eruptive activity. Fumaroles 

 (hot steam and sulphur dioxide) and hot springs (rich in soda) are 

 now found in various parts of the island. 



An excellent map of the island showing the distribution of the 

 chief varieties of lava is given. Petrographic descriptions follow 

 the general summary of events, and this part of the paper is enriched 

 by seventeen analyses. In the succession of lavas as stated above, the 

 average silica percentage of each member is appended, and it becomes 

 clear that the rocks are sharply divided into two main groups, and 

 that the order of succession agrees well with that enunciated by 

 von Richtofen and Iddings, especially as regards the extreme character 

 of the final product. The acidic lavas are remarkable for the consistent 

 absence of nepheline and soda-lime plagioclase. All the felspars 

 are alkalic, averaging Or^ Ab^. The remaining soda is to be found in 

 aegirite and cossyrite, and the excess of silica has crystallized as 



' Note that the main accent is on the i, not on the second e. 



