THE HUMAN OR PRESENT PERIOD. 539 



swept away, and barrenness succeeds productiveness. There are areas 

 in the Orient, once well settled, that are now bare fields of rock on 

 which nothing grows except such few plants as find a foothold in the 

 crevices of the rock. Soils with sandy subsoils have been washed 

 away, leaving barren wastes, and the sands derived from the denuded 

 subsoil have been driven by the winds over adjacent fertile tracts, 

 and by burial have included these in the o common waste. The explana^ 

 tion of much of the former richness and of the present poverty of Oriental 

 peoples no doubt lies in this simple process. This impoverishment 

 of soil threatens many peoples to-day, and is in process of actual reali- 

 zation. 



The glaciated fields are comparatively new grounds for civiliza- 

 tion, and the soil-factor there has a character quite its own. Near 

 the centers of glacial radiation, the old soils were borne away, and 

 new soils were not always developed in equal amount in their stead. 

 A reduced fertility is the result. The half-decayed rock below was 

 largely scraped away, and a long period must ensue before soil-genera- 

 tion will have become effective. These areas lie chiefly in high lati- 

 tudes where other factors compromise human development in its pres- 

 ent state. In the regions of glacial deposition, which fortunately 

 include the greater and the more southerly parts of the glaciated area, 

 a deep sheet of comminuted rock-material, ready for easy conversion 

 into soil by weathering and organic action, covers great plains and 

 has a smoothed topography that aids in restraining its removal. In 

 the peripheral belt of the glaciated area in North America, for a width 

 of 400 or 500 miles, the subsoil of glacial flour and old soil, glacially 

 mixed, has an average thickness of about 100 feet. A similar state- 

 ment may be made of a large, though less, area in north-central Europe. 

 The average thickness of the residuary soils of unglaciated regions 

 similarly situated is about 5 feet. The twenty-fold provision for per- 

 manent fertility thus arising from glaciation seems likely to be a factor 

 of immeasurable importance in the localization of the basal industry 

 of mankind, and of the phases of civilization that are dependent on it. 



With the evolution of the industrial arts, resources which were 

 neglected at first have come to play important parts in the distribu- 

 tion and in the activities of the race, among which are the long and 

 growing lists of mineral resources to which economic geology addresses 

 itself. Chief among these are the metallic ores, the fossil fuels, the 



