The section as a whole affords a striking demonstration of the magnitude of earth-movements since the last of these forests was buried below the surface of a sea in which the volcanic material was deposited. The account of the Yellowstone Park section recalls Darwin's description in the _Naturalist's Voyage_(37) of snow-white columns projecting from a bare slope, at an altitude of 7000 ft. in the Cordillera. The abundance of drift-wood on the coasts of some countries at the present day helps us to picture the conditions under which the remains of former forests have been preserved. In his _Letters from High Latitudes_, Lord Dufferin gives the following description of drift-wood on the shores of Spitzbergen:--'A little to the northward, I observed, lying on the sea-shore innumerable logs of drift-wood. This wood is floated all the way from America by the Gulf Stream, and as I walked from one huge bole to another, I could not help wondering in what primeval forest each had grown, what chance had originally cast them on the waters, and piloted them to this desert shore'(38). A photograph reproduced in Amundsen's book on _The North West Passage_ shows the beach on the Alaskan coast strewn with drifted timber(39). For the accompanying photograph (Fig. 7) of the flood-plain of the Colorado River(40), I am indebted to Professor MacDougal of the Desert Research Laboratory at Tucson, Arizona, who in a recent letter writes, 'During times of high-water a thin sheet of flood covers the flat for many miles and bears drift-wood so thickly that it is difficult to push a boat through it.' The drift-wood consists of poplar, willow, pine, and juniper, 'the last two have been brought from the upper river, from as far away as a thousand miles.' A picture such as this affords an admirable example of the wealth of material available for preservation in a fossil state.