are hot springs with their basins incrusted with calcareous spar, steam jets, geysers, mud volcanoes, waterfalls, caves with stalactites and stalagmites, eroded columns, statues, castles, cathedrals, etc., and a large lake swarming with fish. The valley of the Upper Yellowstone abounds in these wonders. Further details of the topography of the country will be found in the articles on the several States and Territories.
Climate.—The vast area of the United States necessarily exhibits a great variety of climate. New York has the summer of Copenhagen and the winter of Rome, the minimum range of the mercury being 5° in winter, and the maximum 98° in summer. The States bordering on Canada exceed both of these extremes, but throughout the Middle States, lat. 37°-41°, the climate is agreeable and often delightful throughout most of the year. The main peculiarity of the North American seasons is the almost total absence of spring. Mason and Dixon's Line, with its W. extension along the Ohio, Mississippi, and Missouri, has a historical interest, but is also of climatic importance in the geography of the cis-Missouri States. N. of it, sleighs are in frequent use during winter; S. of it, they are seen rarely. To the N. the productions are those of the temperate zone, and the States were always free; to the S., the country becomes more and more tropical as one advances. From meridians 98° to 100° the climate is still variable from year to year, seasons of rain and plenty being followed by others in which drought is the forerunner of scarcity. But the planting of forest trees and the cultivation of the soil, at first by irrigation, has largely increased the amount of rainfall. Along the Pacific seaboard, especially in California, the climate resembles that of S. Europe. The isothermal lines, roughly stated, show a mean temperature of 72° for Florida, the Gulf Shores, and Arizona; of from 52° to 60° for S. of Pennsylvania, Virginia, the N. border of the Carolinas, Tennessee, Missouri, Kansas, S. of Utah and Nevada, and the greater part of California; from 44° to 52° for Massachusetts, New York, Michigan, northern Illinois, Nebraska, Oregon and Washington; and from 36° to 44° for Maine, parts of New Hampshire and Vermont, Wisconsin, Minnesota, the whole crest of the Rocky Mountains, and parts of Oregon and California along the Sierras. The annual rainfall ranges from 56 to 64 inches in the S. of Florida and along the N. W. Pacific coast; 44 to 56 inches over the New Enland coast and the greater part of the Southern States, while in New York, Pennsylvania, Illinois, etc., it is 32-44 inches. In Texas, Indian Territory, eastern Kansas and Nebraska, Dakota and Minnesota, and western California, it is 20-32 inches, while in the tract between 98° and 118° it ranges from 18 to 4 inches. Malarial diseases prevail in the lowlands of most of the Southern States, as also in the new and marshy portions of the Western States below lat. 40° N. Consumption and chest diseases prevail in New England and in the Middle States. Minnesota, Colorado, California, Arkansas, Georgia, and Florida are favorite resorts for persons with weak lungs. On the whole, the climate of the United States may be called healthy, malarious and deadly spots being very few; while certain districts, especially of Florida, the central plains, and the Pacific coast, are among the most salubrious in the world.
Geology and Mineralogy.—Geologically as well as geographically the United States is divided into two great sections by the Rocky Mountains, along whose whole extent, in a wide belt from N. to S., Cretaceous formations predominate, with occasional stretches of Carboniferous strata. Tertiary formations embrace almost the whole of the basin between the Rocky Mountains and the Coast Range, broken by igneous rocks in Washington and in Oregon, and by Metamorphic strata along the Sierras; in the E. section Tertiary formations stretch along the coast from the Rio Grande almost to the Hudson. Metamorphic, igneous, and Devonian rocks prevail in New England, and along the shores of the Great Lakes the Middle Devonian or Old Red Sandstone. Older Palæozoic groups occur in Wisconsin, Ohio, and Tennessee, and run side by side with Metamorphic strata along the Appalachians, while a large proportion of the interior is occupied by great Carboniferous deposits. Anthracite coal occurs in the basins of Pennsylvania, which embrace about 472 square miles, and extend to a depth of from 60 to 100 feet. The Eastern coal fields embrace an area of over 69,000 square miles; the interior, 132,000 square miles; the Gulf, 2,100; the Northern, 88,590; the Rocky Mountain, 37,000, and the Pacific coast, 1,900. (See Coal). The ores of iron abound in the States, and include all known ores. The ore beds most largely worked are in Minnesota, Michigan, Alabama, Wisconsin, New York, Tennessee, Virginia, and New Jersey. Copper ore is found chiefly in Arizona, Michigan, Montana, Utah, Nevada, New Mexico, California, Tennessee, Alaska, Illinois, Kansas and Oklahoma; lead ores (galena) in Missouri, Idaho, Utah, etc., quicksilver in California and Nevada. Gold and silver