REVIEWS 303 
of the physical characters of igneous rocks, their mode of occurrence, 
structure, texture, and composition. In Part II some seventy pages are 
devoted to mineral descriptions, and in the back of the book are four pages 
of tables to be used for the determination of the common rock minerals. 
The usefulness of this part of the work would be greatly increased if it 
contained a colored plate showing the maximum birefringences of minerals 
for various thicknesses of plates. It is presumed that the student has a 
knowledge of optics. Part III is devoted to the classification of igneous 
rocks, the method being essentially the qualitative system now in use. Part 
IV devotes about one hundred pages to the distribution of igneous rocks 
of Great Britain. This part of the work is illustrated by many text figures 
and is a brief summary of the petrography of the British Isles. The work 
is well arranged and includes much useful data. The American student 
of igneous rocks could wish for a rather more comprehensive treatment of 
differentiation, magmatic stopping, and related subjects; with a brief 
résumé of the quantitative system of rock classification, the use of which 
is increasing on this continent. 
Wilsit 
The Ephemeral Volcanic Island in the Iwéjima Group. By T. 
Wakximizu. Publication of the Earthquake Investigation Com- 
mittee in Foreign Languages, No. 22, Section C, Art. 1. With 
Plates I-X1I. T6ky6, 1908. 
The island appeared February 1, 1905, three nautical miles east of 
M. Iwodjima. It was three miles in circumference, 480 feet in height and 
contained about 209 acres in area. The lava was of the olivine-augite- 
andesite type resembling closely that of Mt. Pipe in Iwéjima. From its 
geographic position and nature of ejecta it seemed clear that the ephemeral 
island was a volcano belonging to the same volcanic line as the three 
principal volcanic islands of the Iwdjina group. On June 16, 1905, the 
island had almost disappeared. The cause of submergence was attributed 
to the erosive action of the waves and possibly to depression of the 
crater rim. Ce He 
Formation of Geodes with Remarks on the Silicification of Fossils. 
By Ray S. BAssLer. From the Proceedings of the United States 
National Museum, Vol. XXXV, pp. 133-54, with Plates X VIII— 
XXIV. Washington, 1908. 
The author finds in his study of the formation of geodes in the Keokuk 
geode beds and in the shales and limestones of the Knobstone division of the 
