SECTIONS OF IGNEOUS ROCKS, ILLUSTRATING THE PASSAGE FROM THE
GLASSY TO THE CRYSTALLINE STRUCTURE.

1. Vitreous Rock. 2. Semi-Vitreous Rock. 3. Vitreous Rock with Sphærulites. 4. Rock with
Cryptocrystalline Base. 5. Rock with Microcrystalline Base. 6. Rock of Granitic Structure
built up entirely of Crystals.

[See pp. 53-58.

A

PROFESSOR OF GEOLOGY IN THE ROYAL SCHOOL OF MINES.

University of
MICHIGAN

WITH NINETY-SIX ILLUSTRATIONS.

NEW YORK:

D. APPLETON AND COMPANY,
1, 3, AND 5 BOND STREET.

1881.

PREFACE.

IN PREPARING THIS WORK, I have aimed at carrying out a design suggested to me by the late Mr. Poulett Scrope, the accomplishment of which has been unfortunately delayed, longer than I could have wished, by many pressing duties.

Mr. Scrope's well-known works, entitled 'Volcanoes' and 'The Geology and Extinct Volcanoes of Central France-which passed through several editions in this country, and have been translated into the principal European languages-embody the results of much careful observation and acute reasoning upon the questions which the author made the study of his life. In the first of these works the phenomena of volcanic activity are described, and its causes discussed; in the second it is shown that much insight concerning these problems may be obtained by a study of the ruined and denuded relics of the volcanoes of former geological periods. The appearance of these works, in the years