3. "The Great Ice Age," p. 370.] {p. 9} From the foregoing facts, it seems to me that we are justified in concluding: "1. That however simple and plausible the Lyellian hypothesis may be, or however ingenious the extension or application of it suggested by Dana, it is not sustained by any proof, and the testimony of the rocks seems to be decidedly against it. "2. Though much may yet be learned from a more extended and careful study of the glacial phenomena of all parts of both hemispheres, the facts already gathered _seem to be incompatible with any theory yet advanced_ which makes the Ice period simply a series of telluric phenomena, and so far strengthens the arguments of those who look to extraneous and cosmical causes for the origin of these phenomena."[1] The reader will therefore understand that, in advancing into this argument, he is not invading a realm where Science has already set up her walls and bounds and landmarks; but rather he is entering a forum in which a great debate still goes on, amid the clamor of many tongues. There are four theories by which it has been attempted to explain the Drift. These are: I. The action of great waves and floods of water. II. The action of icebergs. III. The action of glaciers. IV. The action of a continental ice-sheet. We will consider these several theories in their order. [1. "Popular Science Monthly," July, 1876, p. 290.] {p. 10} CHAPTER III. THE ACTION OF WAVES. WHEN men began, for the first time, to study the drift deposits, they believed that they found in them the results of the Noachic Deluge; and hence the Drift was called the Diluvium, and the period of time in which it was laid down was entitled the Diluvial age. It was supposed that-- "Somehow and somewhere in the far north a series of gigantic waves was mysteriously propagated. These waves were supposed to have precipitated themselves upon the land, and then swept madly over mountain and valley alike, carrying along with them a mighty burden of rocks and stones and rubbish. Such deluges were called 'waves of translation.'"[1] There were many difficulties about this theory: In the first place, there was no cause assigned for these waves, which must have been great enough to have swept over the tops of high mountains, for the evidences of the Drift age are found three thousand feet above the Baltic, four thousand feet high in the Grampians of Scotland, and six thousand feet high in New England. In the next place, if this deposit had been swept up from or by the sea, it would contain marks of its origin. The shells of the sea, the bones of fish, the remains of seals and whales, would have been taken up by these great deluges, and carried over the land, and have remained [1. "The Great Ice Age," p. 26.] {p. 11}