Upon the use and interpretation of topographic maps in illustration of characteristic earth features, the following are recommended:— R. D. SALISBURY and W. W. ATWOOD. The Interpretation of Topographic Maps, Prof. Pap., 60 U.S. Geol. Surv., pp. 84, pls. 170. D. W. JOHNSON and F. E. MATTHES. The Relation of Geology to Topography, in Breed and Hosmer’s Principles and Practice of Surveying, vol. 2. Wiley, New York, 1908. GÉNÉRAL BERTHAUT. Topologie, Étude du Terrain, Service Géographique de l’Armée. Paris, 1909, 2 vols., pp. 330 and 674, pls. 265. The United States Geological Survey issues free of charge a list of 100 topographic atlas sheets which illustrate the more important physiographic types. In his “Traité de Géographie Physique”, Professor E. de Martonne has given at the end of each chapter the important foreign maps which illustrate the physiographic types there described. “The Principles of Geology”, by Sir Charles Lyell, published first in three volumes, appeared in the years 1830-1833, and may be said to mark the beginning of modern geology. Later reduced to two volumes, an eleventh edition of the work was issued in 1872 (Appleton) and may be profitably read and studied to-day by all students of geology. Those familiar with the German language will derive both pleasure and profit from a perusal of Neumayr’s “Erdgeschichte” (2d ed. revised by Uhlig. Leipzig and Vienna, 2 vols., 1895-1897), and especially the first volume, “Allgemeine Geologie.” A recent French work to be recommended is Haug’s “Traité de Géologie” (Paris, 1907). Some texts of physical geography may well be consulted, especially Emm. de Martonne’s “Traité de Géographie Physique.” Colin, Paris, 1909, pp. 910, pls. 48, and figs. 396. * * * * * NOTE. An explanatory list of abbreviations used in the reading references follows the List of Illustrations. CHAPTER II THE FIGURE OF THE EARTH =The lithosphere and its envelopes.=—The stony part of the earth is known as the _lithosphere_, of which only a thin surface shell is known to us from direct observation. The relatively unknown central portion, or “core”, is sometimes referred to as the centrosphere. Inclosing the lithosphere is a water envelope, the _hydrosphere_, which comprises the oceans and inland bodies of water, and has a mass 1/4540 that of the lithosphere. If uniformly distributed, the hydrosphere would cover the lithosphere to the depth of about two miles, instead of being collected in basins as it now is. Though apparently not continuous, if we take into account the zone of underground water upon the continents, the hydrosphere may properly be considered as a continuous film about the lithosphere. It is a fact of much significance that all the ocean basins are connected, so that the levels are adjusted to furnish a common record of deposits over the entire surface that is sea-covered.