IN recent years the empirical descriptive methods of an older generation of petrologists have been fortified by exact experimental work in fields of high temperatures and pressures; and some knowledge of the more notable results that have been achieved, and of the fundamental principles of physical chemistry on which they are based, has now become an indispensable part of the equipment of a modern petrologist. The steady stream of publications from the Geophysical Laboratory at Washington, and from various European workers such as Vogt and Niggli. indicates the increasing importance of chemical thermodynamics in revealing the processes which rocks have undergone. Hitherto, however, there has not been in English any systematic introduction to physical chemistry in its application to geological problems. Dr. Rastall will earn the gratitude of a wide range of students by providing this excellent foundation for more extensive studies. Physico-Chemical Geology. By Dr. R. H. Rastall. Pp. vii + 248. (London: Edward Arnold and Co., 1927.) 15s. net.