=The value of the hypothesis.=—Because all the facts necessary for a full interpretation of observed phenomena are not at one’s hand, this should not be made to stand in the way of provisional explanations. If science is to advance, the use of hypothesis is absolutely essential; but the particular hypothesis adopted should be regarded as temporary and as indicating a line of observation or of experimentation which is to be followed in testing it. Thus regarded with an open mind, inadequate hypotheses are eventually found to be untenable, whereas correct explanations of the facts by the same process are confirmed. Most hypotheses of science are but partially correct, for we now “see through a glass darkly”; but even so, if properly tested, the false elements in the hypothesis are one after the other eliminated as the embodied truth is confirmed and enlarged. Thus “working hypothesis” passes into theory and becomes an integral part of science. READING REFERENCES FOR CHAPTER I The most comprehensive of general geological texts written in English is Chamberlin and Salisbury’s “Geology” in three volumes (Henry Holt, 1904-1906), the first volume of which is devoted exclusively to geological processes and their results. An abridged one-volume edition of the work intended for use as a college text was issued in 1906 (College Geology, Henry Holt). Other standard texts are:— SIR ARCHIBALD GEIKIE. Text-book of Geology, 4th ed. 2 vols. London, 1902, pp. 1472. W. B. SCOTT. An Introduction to Geology. 2d ed. Macmillan, 1907, pp. 816. J. D. DANA. Manual of Geology. New edition. American Book Company, 1895, pp. 1087. JOSEPH LECONTE. Elements of Geology. (Revised by Fairchild.) Appleton, 1905, pp. 667. A very valuable guide to the recent literature of dynamical and structural geology is Branner’s “Syllabus of a Course of Lectures on Elementary Geology” (Stanford University, 1908). On the relation of geology to landscape, a number of interesting books have been written:— JAMES GEIKIE. Earth Sculpture or the Origin of Land-Forms. New York and London, 1896, pp. 397. JOHN E. MARR. The Scientific Study of Scenery. Methuen, London, 1900, pp. 368. SIR A. GEIKIE. The Scenery of Scotland. 3d ed. Macmillan, London, 1901, pp. 540. SIR JOHN LUBBOCK. The Scenery of Switzerland and the Causes to which it is Due. Macmillan, London, 1896, pp. 480. LORD AVEBURY. The Scenery of England. Macmillan, London, 1902, pp. 534. SIR A. GEIKIE. Landscape in History, and Other Essays. Macmillan, London, 1905, pp. 352. N. S. SHALER. Aspects of the Earth. Scribners, New York, 1889, pp. 344. G. DE LA NOE ET EMM. DE MARGERIE. Les Formes du Terrain, Service Géographique de l’Armée. Paris, 1888, pp. 205, pls. 48. W. M. DAVIS. Practical Exercises in Physical Geography, with Accompanying Atlas. Ginn and Co., Boston, 1908, pp. 148, pls. 45. JOHN MUIR. The Mountains of California. Unwin, London, 1894, pp. 381.