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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..