THOSE who wish to study the methods of estimating the actual lengths of geological periods should read A. Holmes, The Age of the Earth (Benn’s Sixpenny Series, 1927). which also gives an admirable brief sketch* of historical geology. For the general botanical reader D. H. Scott’s Extinct Plants and Problems of Evolution (Macmillan, 1924) is to be recommended, and the same author’s Studies in Fossil Botany (A. & C. Black, 2 volumes, 3rd edition, 1920 and 1923) is a classic textbook for more advanced students. Plant Life Through the Ages, by A. C. Seward (Cambridge University Press, 2nd edition, 1933) is partly popular and partly suitable for the advanced student. It contains a good bibliography. R. Crookall’s Coal Measure Plants (Arnold, 1929) is of use for identifying impressions of coal plants, and F. J. North’s Coal, and the Coalfields in Wales (National Museum of Wales, 2nd edition, 1931) gives a good detailed account of the nature and formation of coal. All these books, except the first, are well illustrated. Specimens of fossil plants may be seen in the geological or botanical galleries of most museums. The fullest series is in the British Museum (Natural History), South Kensington, where an illustrated Guide to the Fossil PlaJits is obtainable.