Since the first half of the last century, when Pantelleria' figured in the controversy over von Buch's theory of craters of elevation, the geology of the island has been described only by H. Foerstner and A. Bergeat. Through Foerstner's researches the island has become classic in the annals of petrography, because of his discovery there of soda-microcline and the peculiar hornblende, cossyrite, as well as of the occurrence of the remarkable group of pantellerites. In view of the interesting character of its rocks and the rather early date of Foerstner's descriptions and analyses, a re-examination of the island was considered to be desirable. Pantelleria was, therefore, visited in September, 1905, in the course of a trip to the western Mediterranean, undertaken for the Carnegie Institution of Washington. During my stay I met with the utmost courtesy and hospitality, and it is a pleasure to record my thanks to friends on the island, among whom may be specially mentioned Captain G. Herrera, Captain A. Pocobelli, Lieutenant A. Innorta, and Doctor S. Granone. To Professor J. Volney Lewis I am indebted for making the photographs of the rock sections.