The plain, precious in peaceful times, affords a poor shelter when war is raging.
So, also, the value of the different qualities of ground varies in different epochs. In the times when agricultural resources constituted the only or principal element of wealth, all the advantages appertained to lands in which the best qualities for tillage were combined. In the present age, the natural geological constitution of the soil is not of such paramount importance. As the earth has become better known, as scientific conditions of fertility have been ascertained through chemical analysis, man has learned to improve Nature by adding to soils the indispensable elements they did not already possess. Mechanical progress, creating increased facilities for transportation, and giving more perfect agricultural tools, has acted in the same direction. There is no soil so refractory that it may not be brought to reason by suitable application of fertilizing or corrective elements. By means of agricultural geology, which has been raised to a science, man can completely transform the natural value of any soil.
Different sorts of land have likewise values for mining not less unequal than their adaptations to agriculture. The minerals and coal with which industry is fed, and which have become the principal factors of wealth and power, have not been distributed at hazard over the globe. The beds exist in direct relation with the geological constitution. When we compare the fitness of different lands for mining and for agriculture, we most often find an incompatibility of qualities. The primary mineral and coal lands, when decomposed, yield chiefly hard gravels, cold and sterile. Secondary and Tertiary soils, on the other hand, almost destitute of minerals, most often have the looseness and the variety of composition that render them most friendly to remunerative cultivation. In view of these contrasts we are able to comprehend the importance of the revolution which modern scientific advance has provoked in causing preponderance of economical advantages to pass from agricultural fitness to adaptation to mineral and industrial exploitation. The equilibrium of the regions of the earth has been disturbed. Countries long neglected on account of their barrenness have been peopled all of a sudden because they contained coal; while other countries, which by virtue of their excellent agricultural soil had become chief centers of life, find themselves relegated to the second rank because that same rich agricultural soil affords nothing in the way of manufacturing facilities.
All climates, likewise, are not equally agreeable to man. Some are unhealthy, like those of marshy regions and equatorial countries, and hinder man's establishment within them, or condemn him to a
