.

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..