Abstract: A RICH store of observations especially on the metamorphic rocks of Great Britain, numerous excellent drawings of rock sections as seen in the microscope and admirable clarity of statement are the outstanding features of this new book on metamorphism. In the first part, which is devoted to thermal metamorphism, general genetic considerations occupy about one-third of the space and are followed by a detailed account of the thermal metamorphism of argillaceous, calcareous and siliceous sediments and of igneous rocks. Especially in connexion with the last named, much interesting information is given. The second part treats in similar fashion of dynamic and regional metamorphism with very brief chapters devoted to injection, repeated and retrograde metamorphism. Metamorphism: a Study of the Transformations of Rock-Masses. By Dr. Alfred Harker. Pp. x + 360. (London: Methuen and Co., Ltd., 1932.) 17s. 6d. net.