The third free public lecture in the University Museum course will be given tomorrow afternoon at 3.30 o'clock in the Geological Lecture Room of the University Museum by Professor W. M. Davis '69, whose subject will be "Why the Earth is Believed to be Millions of Years Old." The lecture will be in part explanatory of certain exhibits, included in the New Geological Exhibition Room, now in process of arrangement, and will attempt to make clear why the geological history of the earth is divided into various ages and periods, each of which is of untold duration. Photographic projections will present illustrations of various rock structures, from which the processes and conditions of past ages may be reasonably inferred, and the essentially simple nature of much of the evidence on which geological conclusions are based will be considered in some detail.