_Athenæum._ Prof. Lewis has written a valuable work.... The present work deserves to be welcomed not only as a greatly needed help to advanced students of mineralogy, but as a sign that the study itself maintains an honoured place in the university Science Course. _Nature._ The author and the University Press may be congratulated on the completion of a treatise worthy of the subject and of the University. =Petrology for Students.= An Introduction to the Study of Rocks under the Microscope. By A. Harker, M.A., F.G.S., Fellow of St John's College, and Demonstrator in Geology (Petrology) in the University of Cambridge. Crown 8vo. Second Edition, Revised. 7_s._ 6_d._ _Nature._ No better introduction to the study of petrology could be desired than is afforded by Mr Harker's volume. London: C. J. CLAY AND SONS, CAMBRIDGE UNIVERSITY PRESS WAREHOUSE, AVE MARIA LANE AND H. K. LEWIS, 136, GOWER STREET, W.C. _Medical Publisher and Bookseller._ Transcriber's Note Any obsolete or alternate spelling and grammar was retained. All obvious typographical errors were corrected. Although hyphenation of words has been standardized to the most prevalent occurrence, the six occurrences of fresh-water were not converted to freshwater (30 occurrences) due to usage. Corrected spellings: Godwin-Austen (p. 20); Whidbourne (p. 191); and Ichthyopterygia (p. 223). End of the Project Gutenberg EBook of The Principles of Stratigraphical Geology, by J. E. Marr