traveller, whom Alexander von Humboldt calls "dem geistreichen Forscher der Natur," the above are selected as being the most important. That on the Canaries is accompanied by a large atlas, in which the volcanoes of Teneriffe, Palma, and Lancerote, with some others, are elaborately represented, and are considered to bear out the author's views regarding the formation of volcanic cones by elevation or upheaval. The works dealing with the volcanic phenomena of Central and Southern Italy are also written with the object, in part at least, of illustrating and supporting the same theoretical views; with these we have to deal in the next chapter.

5. Dr. Charles Daubeny, F.R.S., Description of Active and Extinct Volcanoes, of Earthquakes, and of Thermal Springs, with remarks on the causes of these phenomena, the character of their respective products, and their influence on the past and present condition of the globe (2nd edition, 1848). In this work the author gives detailed descriptions of almost all the known volcanic districts of the globe, and defends what is called "the chemical theory of volcanic action"—a theory at one time held by Sir Humphrey Davy.

6. Wolfgang Sartorius von Waltershausen, Der Ætna. This work possesses a melancholy interest from the fact that its distinguished author did not live to see its publication. Von Waltershausen, having spent several years in making an elaborate survey of Etna, produced an atlas containing numerous detailed maps, views, and drawings of this mountain and its surroundings, which were published at Weimar by Engelmann in 1858. A description in MS. to accompany the atlas was also prepared, but before it was printed, the author died, on the 16th October 1876. The MS. having been put into the hands of the late Professor Arnold von Lasaulx by the publisher of the atlas, it was subsequently brought out under the care of this distinguished petrologist, who was so fully fitted for an undertaking of this kind.

7. Sir Charles Lyell in his Principles of Geology[10] devotes several chapters to the consideration of volcanic phenomena, in which, being in harmony with the views of his friend, Poulett Scrope, he combats the "elevation theory" of Von Buch, as applied to the formation of volcanic mountains, holding that they are built up of ashes, stones, and scoriæ blown out of the throat of the volcano and piled around the orifice in a conical form. Together with these materials are sheets of lava extruded in a molten condition from the sides or throat of the crater itself.

8. Professor J. W. Judd, F.R.S., in his able work entitled, Volcanoes: What they are, and what they teach,[11] has furnished the student of vulcanicity with a very complete manual of a general character on the subject. The author, having extensive personal acquaintance with the volcanoes of the south of Europe and the volcanic rocks of the British Isles, was well equipped for undertaking a work of the kind; and in it he supports the views of Lyell and Scrope regarding the mode of formation of volcanic mountains.

9. Sir Archibald Geikie, F.R.S., in his elaborate monograph[12] on the Tertiary Volcanic Rocks of the British Isles, has recorded his views regarding the origin and succession of the plateau basalts and associated rocks over the region extending from the north of Ireland to the Inner Hebrides; and in dealing with these districts in the following pages I have made extensive use of his observations and conclusions.

10. Report published by the Royal Society on the Eruption of Krakatoa—drawn up by several authors (1885)—and the work on the same subject by Chev. Verbeek, and published by the Government of the Netherlands (1886). In these works all the phenomena connected with the extraordinary eruptions of Krakatoa in 1883 are carefully noted and scientifically discussed, and illustrated by maps and drawings.

11. The Charleston Earthquake of August 31, 1886, by Captain Clarence Edward Dutton, U.S. Ordnance Corps. Ninth Annual Report of the United States Geological Survey, 1887-88, with maps and illustrations.

12. Amongst other works which may be consulted with advantage is that of Mr. T. Mellard Reade on The Origin of Mountain Ranges; the Rev. Osmond Fisher's Physics of the Earth; Professor G. H. Darwin and Mr. C. Davison on "The Internal Tension of the Earth's Crust," Philosophical Transactions of the Royal Society, vol. 178; Mr. R. Mallet, "On the Dynamics of Earthquakes," Trans. Roy. Irish Academy, vol. xxi.; Professor O'Reilly's "Catalogues of Earthquakes," Trans. Roy. Irish Academy, vol. xxviii. (1884 and 1888); and Mr. A. Ent. Gooch On the Causes of Volcanic Action (London, 1890). These and other authorities will be referred to in the text.