III. On the Reason why the Difference of Reading between a Thermometer exposed to direct Sunshine and One Shaded diminishes as we ascend in the Atmosphere 547 IV. Remarks on Mr. J. Y. Buchanan’s Theory of the Vertical Distribution of Temperature of the Ocean 550 V. On the Cause of the Cooling Effect produced on Solids by Tension 552 VI. The Cause of Regelation 554 VII. List of Papers which have appeared in Dr. A. Petermann’s _Geographische Mittheilungen_ relating to the Gulf-stream and Thermal Condition of the Arctic Regions 556 VIII. List of Papers by the Author to which Reference is made in this Volume 560 INDEX 563 LIST OF PLATES. EARTH’S ORBIT WHEN ECCENTRICITY IS AT ITS SUPERIOR LIMIT _Frontispiece._ PLATE I. SHOWING AGREEMENT BETWEEN THE SYSTEM OF OCEAN-CURRENTS AND WINDS _To face page_ 212 II. SHOWING HOW OPPOSING CURRENTS INTERSECT EACH OTHER 219 III. SECTION OF MID-ATLANTIC 222 IV. DIAGRAM REPRESENTING THE VARIATIONS OF ECCENTRICITY OF THE EARTH’S ORBIT 313 V. SHOWING PROBABLE PATH OF THE ICE IN NORTH-WESTERN EUROPE 449 VI. SHOWING PATH OF ICE ACROSS CAITHNESS 453 VII. MAP OF THE MIDLAND VALLEY (SCOTLAND), SHOWING BURIED RIVER CHANNELS 471 CHAPTER I. INTRODUCTION. The Fundamental Problem of Geology.—Geology a Dynamical Science.—The Nature of a Geological Principle.—Theories of Geological Climate.—Geological Climate dependent on Astronomical Causes.—An Important Consideration overlooked.—Abstract of the Line of Argument pursued in the Volume.