In the non-glaciated parts of the continent occur stratified Pleistocene deposits, which it is very difficult to associate with the events taking place in the glaciated area, for lack of any means of direct comparison. On the Atlantic slope from New Jersey southward a succession of Pleistocene gravels and sands constitutes the Columbian formation, so called because of its typical development in the District of Columbia. These deposits are differently interpreted by those who have examined them, but they appear to be largely fluviatile and subaerial much like the Pliocene Lafayette. Three parts of the Columbia formation have been recognized which by some authorities are regarded as three successive depressions and emergences from the sea, but the difficulties in this interpretation are such that a non-marine origin is more probable. On the other hand, marine fossils in the uppermost of the three divisions in the Chesapeake Bay region indicate some depression in that area. All the divisions contain large boulders transported by floating ice.

Over the Great Plains from South Dakota to Texas the surface formation is a fine, calcareous, sandy clay, which lies unconform-ably upon the eroded surfaces of older strata, from the Blanco to the Cretaceous. This formation has been called the Sheridan stage ("Equus Beds"), from Sheridan County, Nebraska, where it is typically displayed. It is, to a large extent, of aeolian origin and in places contains great numbers of fossil bones. In South Dakota the Sheridan passes under a drift sheet, and probably it corresponds to one of the earlier interglacial stages.

In the Great Basin, the later Pleistocene had, temporarily at least, a much less arid climate than at present, as is indicated by the many lakes which it contained, and two of these, Lakes Bonneville andLahontan, were very large (see p. 219). The former, which was in the eastern part of the Great Basin, had an outlet northward to the Snake River, and had two periods of expansion, separated by one of almost complete desiccation. Lake Lahontan, which had no outlet, had similar episodes of rise and fall.

On the Pacific coast, marine Pleistocene in two unconformable stages occurs in southern California; the fauna of the lower stage has still a somewhat northern character, but in the upper stage the water became warmer than it is now, and tropical species which no longer live on the California coast were present. Pleistocene movements affected the Pacific coast to the amount of 3000 feet in the Inyo Mountains of California, 200 feet or more on the coast of Oregon, and 4000 feet in southeastern Alaska, and increased the height of the Sierra, Wasatch, and Basin ranges and of the high plateaus of Utah and Arizona.

The volcanic activity which had been so very striking during the Tertiary period in the western region continued into the Pleistocene, as is to be seen in the lava flows of the Great Basin, Arizona, New Mexico, Idaho, all the Pacific States, and Alaska.

The late Pleistocene was a time of ameliorated climate and heavy rainfall, when the flooded rivers moved sluggishly, owing to the diminished slope, and spread sheets of sands, gravels, and clays over their flood plains and in their estuaries, through which they have subsequently cut terraces, when elevation had given them renewed power.

The events of the Glacial epoch, and the diastrophic movements which accompanied and followed it, have had the most important and widespread effects upon the topography of the glaciated regions. The sheets of drift, stratified and unstratified, have completely changed the surface of the country, and by filling up the pre-Glacial valleys, have revolutionized the drainage, only the largest streams being able to regain their old courses. Innumerable lakes, large and small, were formed in depressions, rock basins, and behind morainic dams, the contrast between the glaciated and non-glaciated regions in regard to the number of lakes in each being very striking.

The Pleistocene was closed and the Recent epoch inaugurated by a movement of upheaval which raised the continent to its present height. These Pleistocene movements have been correlated with the accumulation and removal of the ice, and it is at least a curious coincidence that the continent should have slowly sunk under the maximum load of ice and have risen again after the ice had melted. These movements were greatest where the ice was thickest.