of an island environment—­Islands as places of refuge—­Islands as places of survival—­Effects of small area in islands—­Economic limitations of their small area—­Dense population of islands—­Geographic causes of this density—­Oceanic climate as factor—­Relation of density to size—­Density affected by a focal location for trade—­Overflow of island population and colonies to the mainland—­Precocious development of island agriculture—­Intensive tillage—­Emigration and colonization from islands—­Recent emigration from islands—­Maritime enterprise as outlet—­Artificial checks to population—­Polyandry—­Infanticide—­Low valuation of human life.

CHAPTER XIV.  PLAINS, STEPPES AND DESERTS

Relief of the sea floor—­Mean elevations of the continents—­Distribution of relief—­Homologous reliefs and homologous histories—­Anthropo-geography of lowlands—­Extensive plains unfavorable to early development—­Conditions for fusion in plains—­Retardation due to monotonous environment—­Influence of slight geographic features in plains—­Plains and political expansion—­Arid plains—­Nomadism—­Pastoral life—­Pastoral nomads of Arctic plains—­Historical importance of steppe nomads—­Mobility of pastoral nomads—­Seasonal migrations—­Marauding expeditions—­Forms of defense against nomad depredations—­Pastoral life as a training for soldiers—­Capacity for political organization and consolidation—­Centralization versus decentralization in nomadism—­Spirit of independence among nomads—­Resistance to conquest—­Curtailment of nomadism—­Supplementary agriculture of pastoral nomadism—­Irrigation and horticulture—­Scant diet of nomads—­Effects of a diminishing water supply—­Checks to population—­Trade of nomads—­Pastoral nomads as middlemen—­Desert markets—­Nomad industries—­Arid lands as areas of arrested development—­Mental and moral qualities of nomads—­Religion of pastoral nomads.

CHAPTER XV.  MOUNTAIN BARRIERS AND THEIR PASSES

Man as part of the mobile envelope of the earth—­Inaccessibility of mountains—­Mountains as transit regions—­Transition forms of relief between highlands and lowlands—­Piedmont belts as boundary zones—­Density of population in piedmont belts—­Piedmont towns and cities—­Piedmonts as colonial or backwoods frontiers—­Mountain carriers—­Power of mountain barriers to block or deflect historical movement—­Significance of mountain valleys—­Longitudinal valleys—­Passes in mountain barriers—­Breadth of mountain barriers—­Dominant transmontane routes—­Height and form of mountain barriers—­Contrasted accessibility of opposite slopes—­Political and ethnic effects—­Persistence of barrier nature—­Importance of mountain passes—­Geographic conditions affecting the historical importance of passes—­Passes determine the transmontane routes—­Navigable river approaches to passes—­Types of settlement in the valley approaches—­Pass cities and their markets—­Pass peoples—­Their political importance.