II. IN a notice (NATURE, vol. xxxv. p. 482) of the first part of the present work, we showed that the author, adopting a natural system of classification which gives the first place to field-evidence, divides the eruptive rocks into three great groups, viz. (1) the Plutonic rocks; (2) the Dyke rocks (Ganggesteine); and (3) the Volcanic or Effusive rocks. Unable to free himself entirely from the idea that geological age ought to be an essential factor in rock-classification, he subdivides the third group into a palaeo-volcanic and a neo-volcanic series. It is the treatment of the neo-volcanic series which constitutes the bulk of this, the second and final part of the book. Mikroskopische Physiographie der massigen Gesteine. Von H. Rosenbusch. II. Abtheilung. Zweite ganzlich umgearbeitete Auflage. (Stuttgart, 1887.)