different aspects. The seismic history of February, 1943, is interesting, indicating that the deep-focus earthquakes recorded during that time did not have their epicenters where the volcano appeared and that the temblors near Paricutin just before the eventful February 20 were largely local in effect. Professor L. C. Graton of Harvard gives an admirable discussion of the deeper implications of the geological studies and the problem of the source of volcanoes, together with an elucidation of the opportunities offered to science through daily observation of the growth of the mass instead of confrontation of a tremendous pile integrating all the aspects of volcanology in an overwhelming single three-dimensional puzzle first seen long after its formation. Eduardo Schmitter's description of the typical rocks of different stages in the eruption, with its color plates and its comparison of Paricutin's rocks with those of neighboring cones, marks the beginning of a promising study and comparison of rock textures and compositions, which, in Mexico, could yield much information on volcanological sequences in one of the world's richest fields.-F. H. POUGH