Remarks on the Drift Deposits.—Examination of Drift by Borings.—Buried River Channel from Kilsyth to Grangemouth.—Channels not excavated by Sea nor by Ice.—Section of buried Channel at Grangemouth.—Mr. Milne Home’s Theory.—German Ocean dry Land.—Buried River Channel from Kilsyth to the Clyde.—Journal of Borings.—Marine Origin of the Drift Deposits.—Evidence of Inter-glacial Periods.—Oscillations of Sea-Level.—Other buried River Channels 466 CHAPTER XXX. THE PHYSICAL CAUSE OF THE MOTION OF GLACIERS.—THEORIES OF GLACIER-MOTION. Why the Question of Glacier-motion has been found to be so difficult.—The Regelation Theory.—It accounts for the Continuity of a Glacier, but not for its Motion.—Gravitation proved by Canon Moseley insufficient to shear the Ice of a Glacier.—Mr. Matthew’s Experiment.—No Parallel between the bending of an Ice Plank and the shearing of a Glacier.—Mr. Ball’s Objection to Canon Moseley’s Experiment.—Canon Moseley’s Method of determining the Unit of Shear.—Defect of Method.—Motion of a Glacier in some Way dependent on Heat.—Canon Moseley’s Theory.—Objections to his Theory.—Professor James Thomson’s Theory.—This Theory fails to explain Glacier-motion.—De Saussure and Hopkins’s “Sliding” Theories.—M. Charpentier’s “Dilatation” Theory.—Important Element in the Theory 495 CHAPTER XXXI. THE PHYSICAL CAUSE OF THE MOTION OF GLACIERS.—THE MOLECULAR THEORY. Present State of the Question.—Heat necessary to the Motion of a Glacier.—Ice does not shear in the Solid State.—Motion of a Glacier _molecular_.—How Heat is transmitted through Ice.—Momentary Loss of Shearing Force.—The _Rationale_ of Regelation.—The Origin of “Crevasses.”—Effects of Tension.—Modification of Theory.—Fluid Molecules crystallize in Interstices.—Expansive Force of crystallizing Molecules a Cause of Motion.—Internal molecular Pressure the chief Moving Power.—How Ice can excavate a Rock Basin.—How Ice can ascend a Slope.—How deep River Valleys are striated across.—A remarkable Example in the Valley of the Tay.—How Boulders can he carried from a lower to a higher Level 514 APPENDIX. I. Opinions expressed previous to 1864 regarding the Influence of the Eccentricity of the Earth’s Orbit on Climate 528 II. On the Nature of Heat-Vibrations 544