During the last (Permian) period of the Paleozoic era the marine waters of the west, and the alternating shallow tidewater, swamps, and near sea level lands of the east gradually gave way to dry lands, so that by the close of the period marine water covered only a small part of the Southwest from Oklahoma across central Texas to southern California and northwestern Mexico, where strata as much as several thousand feet thick formed. In the middle western part of the area of the United States, especially from northern Texas to Nebraska and Wyoming, the climate was arid and red strata (so-called "Red Beds"), salt, and gypsum were extensively deposited on land and in great salt lakes or more or less cut-off arms of the sea. Strata commonly from 2,000 to 7,000 feet thick were there deposited. Similar conditions prevailed in parts of Nova Scotia, New Brunswick, and Newfoundland, where strata 8,000 feet thick accumulated. Over the site of most of the Appalachians the coal swamp conditions, with local sea incursions, continued from the preceding period, as shown by the character of the strata (1,000 feet thick) containing some coal. Vigorous volcanic activity which, as already mentioned, began in the Mississippian period from northern California to Alaska continued not only through the Pennsylvanian and Permian but also into the early Mesozoic era, as shown by the great quantities of volcanic materials associated with rocks of those ages. The Permian presents a puzzling combination of climatic conditions which causes it to stand out in marked contrast against the generally mild and uniform climates of nearly all of preceding Paleozoic time. Most remarkable of all are the records of a great Ice Age during early Permian time. One surprising fact is the widespread distribution of the glacial deposits in both the north and south temperate zones, and even well within the torrid zone. They are perhaps most extensive and best known in Australia, South Africa, India, and Brazil. Glacial deposits almost certainly of the same age on smaller scales occur in eastern Massachusetts, southern England, eastern Russia and the Caucasus region. Although the areas occupied by the Permian glaciers, which in many cases must have been extensive ice sheets, cannot be accurately delimited, it is, nevertheless, quite certain that the ice was notably more extensively developed than it was during the great "Ice Age" of late (Quaternary) geologic time. Another surprising fact is that certain of the glaciers must have come down to, or nearly to, sea level, as shown by the direct association of marine strata with glacial deposits. Thus, in southern Australia at least eight beds of glacial materials (some of them 100 to 200 feet thick) occur within true marine strata 2,000 feet thick. A third remarkable fact is that the Permian Ice Age, like the Quaternary Ice Age, had interglacial epochs of relatively mild climate, as proved by the occurrences of beds of coal