The Lithosphere or Solid the home of man and the source of most of the products he utilizes, the lands hold the largest place in the research of the physiographer. Here he is faced with two problems; a study of the origin of land forms, and the determi nation of the influence of land forms on man and his pursuits. The first of these problems has already received attention in the section on Dynamical Geology, under title of GEOLOGY. The second will be briefly considered below. The major relief features of the lands are plains, plateaus and mountains, and each has its own characteristic effect on life of all kinds.
Plains.— Plains are of several varieties. Coastal plains lie between the shore line and the higher, often mountainous, interior. A typical example is the Atlantic coastal plain. Not all coasts have such plains, but when they do, the region is usually one recently emerged from the sea. It is likely, therefore, to have long straight coasts and few harbors. A slight recent sinking of parts of the Atlantic Coast of the United States has fortunately resulted in good harbors. Because coastal plains are re cently emerged sea bottom, and because when submerged they were being overspread with sand deposits their soil is frequently sandy. The Atlantic Coastal Plain has large stretches of infertile soil, but because it faces America's greatest market — Europe, and has good har bors, it has undergone rapid development. Flood plains and delta plains on the larger rivers are often very extensive. The rivers are slug gish, carrying little coarse sand or gravel, and from year to year in time of flood they have spread out broad layers of fine rich soil until they comprise some of the richest agricultural lands of the world. They are usually densely populated with an intelligent and progressive class of people. Their most serious drawback is from flooding, which takes toll of many lives, and millions of dollars' worth of property each year, on the great flood plains of the world, like those of the Mississippi, Nile, Ganges, Danube and the Hoang Ho. Many other types of plains are known, and each has its character istic relation to human activity.
Plateaus. Plateaus are elevated plains, usually bordering or enclosed by mountain ranges. For this reason they are often cut off from rain bearing winds and are semi-arid, as our western 'Great Plains," (more properly spoken of as plateaus) and the Columbia Plateau ; or truly desert, as most of the °Great Basin,' which is, properly speaking, a plateau carrying mountain ranges on its extensive surface. Some of the
very elevated plateaus, such as the Colorado Plateau, rise so high that, even in the midst of deserts, they receive enough rain to support splendid forests. Because of their great eleva tion and sometimes due to their aridity and isolation by mountain chains, plateaus are less favorable to population than plains. Where these high plains are deeply dissected, as in the Allegheny and Cumberland plateau region, they are often called mountains, and resemble these latter in their effect on civilization.
Mountains. These are the most striking of nature's forms and contain the grandest scenery in the world. They are also of profound in fluence on all life history. For the most part rocky, isolated and inhospitable, they form rather barriers than homes. It is true that mountains have many times in the history of the world offered asylums to weaker peoples, driven out of other lands by religious or polit ical persecution, but their most important role is to act as barriers. They deflect winds or rob them of their rain, so that in • the lee of mountains often lie deserts. They prevent the migration of many types of plants and even some members of the animal kingdom. Even to man they present serious obstacles to travel and transportation, more so formerly than now. In the isolated valleys of the more remote mountain regions are crowded the stragglers of the world's migrations, and there, old customs, traditions and manners of speech are preserved among ignorant and illiterate peoples long after they are forgotten elsewhere. Because moun tains are often the seat of extensive volcanic activity, and because volcanic processes are largely responsible for deposits of valuable metals, mountains are often important mining regions. It is the search for metallic wealth more than anything else that has peopled moun tain regions with progressive populations, and except along tourist routes, few important cities exist in mountainous areas other than in mining districts.