Coffee and Tea as Products of Rugged Regions.—What has been said above applies to certain tropical crops as well as to those of more northern regions. Coffee and tea can be raised on slopes as well as on plains, for they need abundance of both sun and rain and must have good drainage, while in the hotter regions of its growth the coffee also needs • shade. These conditions are well met where winds from the ocean blow over mountains, as in Brazil, Ceylon, the eastern Himalayas of Assam, and southeastern China. In such places showers are frequent enough to keep the ground moist, yet the sun shines much of the time and the ground does not become waterlogged.
In the table of the world's chief products (page 14) those produced almost wholly in cyclonic regions arc double starred, those produced in both cyclonic and other regions have a single star, and those derived chiefly from non-cyclonic regions are not marked. Of the six organic products which come chiefly from non-cyclonic regions three, namely, coffee, tea, and rubber, can be produced as well or better in rugged regions than in plains, while three, rice, millet, and cotton, are better adapted to the plains. On the other hand, of the ten organic products which are limited largely to cyclonic regions, namely, wheat, potatoes, dairy products, oats, rye, barley, swine, raw silk, hay and horses, the only one which is as well adapted to rugged regions as to plains is raw silk, which may be called a tree crop. This raises the question whether in the future the rugged regions of the tropics are more likely to yield a great abundance and variety of products than arc the rugged regions of cooler climates.
The Relation of Metallic Ores to is well known that most ores are found among mountains. Ores, it will be remembered, are rocks which contain an unusually large per cent of certain metals which are scattered in minute quantities in almost all rocks. It is also well known that the quantity of metallic ores varies greatly from one mountain system to another. For example, in North America the eastern mountains forming the Appalachian system contain relatively little ore aside from low-grade iron. On the other hand the western mountains contain a great variety and abundance of ores distributed all the way from Alaska to Mexico. A similar condition prevails in Europe. Except for the abundant and excellent iron ores of Sweden, the northwestern mountains from Ireland and Scotland through Scandi navia to Finland contain almost as few ores as do the Appalachians.
The Alps likewise supply almost no metals. The only mountains in central or western Europe that contain many ores other than iron are those of Bohemia and the neighboring parts of Germany, but even there the supply is small. Only in the southern peninsulas of Spain, Italy, and the Balkans and in the eastern ranges of the Urals and Caucasus is there a great variety and abundance of metallic ores. Farther east in Turkey, Persia, and Central Asia, valuable ores appear to be as numerous as in the similar parts of North America. Correspond ing conditions are found in the other continents, namely, few ores in some of the mountains and many in others. In every case the greatest variety and abundance of ores is found not only in regions of rugged relief, but to a large extent in the drier parts of the continent.
Why Ores are Found Among us first see why productive metallic ores are largely limited to mountainous regions, and then why they occur chiefly in dry regions. Five reasons for their occurrence among mountains are commonly given, while a sixth and more important reason is less emphasized. (1) In rugged regions the earth's surface is deeply gashed by valleys, thus exposing the rocks to a depth of hundreds or thousands of feet. (2) The rocks of rugged regions have generally been much folded and crumpled, thus bringing to the surface many formations which even the deepest valleys would otherwise never penetrate. (3) Where the slopes are steep the soil is thin, and bare rock is exposed so that valuable minerals can easily be discovered. In regions of low relief on the contrary the soil is often so deep that no rock is visible for miles. (4) Among mountains the chief process is erosion whereby new and deeper layers are brought to light. In level regions the most important geological processes are generally the weathering and deposition of soil, thus covering the under lying rocks deeper and deeper. (5) The heavy metals, gold and plati num, form placer deposits such as those of California and the Urals only where the slopes are steep enough so that the fragments of metal can be carried by running water. In such cases bits of metal from a wide area are brought together by tributary streams and carried in a main stream until it reaches relatively gentle slopes and begins to flow so slowly that the heavy metal falls to the bottom, while all but a small fraction of the stream's load of gravel, sand and silt is carried further.