COLLATERAL READING[6]
Gibbins's History of Commerce—Chapters IV-V.
Fiske's Discovery of America, Vol. 1—Chapters IV-V.
CHAPTER III
TOPOGRAPHIC CONTROL OF COMMERCE
The great industry of commerce, which includes both the trade in the commodities of life and the transportation of them, is governed very largely by the character of the earth's surface. But very few food-stuffs can be grown economically in mountain-regions. Steep mountain-slopes are apt to be destitute of soil; moreover, even the mountain-valleys are apt to be difficult of access, and in such cases the cost of moving the crops may be greater than the market value of the products. Mountainous countries, therefore, are apt to be sparsely peopled regions.
But although the great mountain-systems are unhabitable, or at least sparsely peopled, they have a very definite place in the economics of life. Thus, the great western highland of the United States diverts the flow of moisture from the Gulf of Mexico northward into the central plain, and gives to the region most of its food-growing power. In a similar manner, moisture intercepted by the Alps and the Himalayas has not only created the plains of the Po and the Ganges from the rock-waste carried from the slopes, but has also made them exceedingly fertile.
Mountain-ranges are also valuable for their contents. The broken condition of the rock-folds and the rapid weathering to which they are subjected have exposed the minerals and metals so useful in the arts of commerce and civilization. Thus, the weathering of the Appalachian folds has made accessible about the only available anthracite coal measures yet worked; and the worn folds about Lake Superior have yielded the ores that have made the United States the foremost copper and steel manufacturing country of the world. Gold, silver, tin, lead, zinc, platinum, granite, slate, and marble occur mainly in mountain-folds.