Another important fact respecting this glacial draft consists in the universal absence of marine, as well as fresh-water fossils in its interior--a fact which strengthens the view that they have been accumulated by the agency of strictly terrestrial glaciers; such is, at least, the case everywhere far from the sea-shore. But we may conclude that these ancient glaciers reached, upon various points, the sea-shore at the time of their greatest extension, just as they do at present in Spitzbergen and other arctic shores; and that therefore, in such proximity, phenomena of contact should be observed, indicating the onward movement of glacial material into the ocean, such as the accumulation within these materials of marine fossil remains, and also the influence of the tidal movements upon them. And now such is really the case. Nearer the sea-shores we observe distinctly, in some accumulations of the drift, faint indications of the action of the tide, reaching the lower surface of glaciers, and the remodelling to some extent of the materials which these poured into the sea. A beautiful example of the kind may be observed near Cambridge, along Charles River, not far from Mount Auburn, where the unstratified glacial drift (_a_) presents in its upper masses strictly the characters of true terrestrial glacial accumulation, but shews underneath faint indications (_b_) of the action of tides. Above, regular tidal strata (_c_) are observed, formed probably after the masses below had subsided. The surface of this accumulation is covered with soil (_d_). [Illustration: Sketch of river bank stratification]