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 The width of the forest belt is also a matter of great impor- tance, for in eastern Peru and Bolivia the forest is broad anc the growth dense. As we go southward the forest becomes more patchy in character. [t narrows down to a well-defined band on the mountain side that can sometimes be seen in its whole breadth from a single viewpoint. There are gaps or “passes” through it. Transit up and down the mountain valleys through the forest zone is here unhindered by the growth of jungle or dense stands of trees. Though there is a wet season it is of short duration, and the floods in the rivers have less force. The trails are easier to maintain, Trade is more regular. The distances to be covered may be as great as farther north, but the time of passage is shorter. It is easy to think that under these conditions the effect of the plain upon the mountain population of the Puna in drawing it away from its Pacific outlets is obvious; but the obviousness disappears when we see that, in spite of the far greater difficulties of the passage in eastern Peru and Bolivia and in spite of the inviting rivers that flow down into the Amazon basin, the mountain continues to attract the trade of the eastern valleys and the bordering plain.

In the eastern mountain belt of Peru and Bolivia there is a permanent gap of several thousand feet vertical elevation be- tween the zone of snow and the zone of forest. The belt of maximum rainfall lies between 5000 and Soco feet. The cold timber line runs from gooo to 10,500 feet, with a few outleirs of stunted woodland as far as 12,500 feet. In secluded valleys deep set among the eastern mountains a dry timber line occurs in places around 3000 feet with many variations in elevation due to the variable declivity, the exposure of the slopes, and the degree of seclusion of the valleys. So we find permanent habitations but little below the snow line and a group of dis- tinctive high mountain folk widely distributed throughout the pasture belt. If the alpine meadows of these mountains are