It is interesting to watch the changes as one descends eastward from high elevations in the Andes. At the crest all is sterile--nothing but bare rocks, with possibly a few mosses clinging to their sides. No water is visible, but by and by we find a tiny thread formed by the melting snows, or the condensed vapor from the eastern winds. The thread enlarges; after a time it grows to a brook, with little pools here and there in which a cup can be dipped, or our tired animals can drink. Most of the mountain trails follow the valleys and ravines which form the natural channels of the water, and so hour by hour the brook increases in width and volume. The mosses on the rocks grow more dense, they give place to shrubs, and the shrubs in turn give place to bushes. Then come stunted trees, only a few inches in height, but having the form and appearance of perfect trees, gnarled and twisted by the wintry blasts. The stunted trees are less and less dwarfed, and from inches they increase in height to feet. The ground is covered with grass, at first, in stray bunches, as though life was a struggle under the low temperature constantly surrounding them. The bunches increase in number till they become a carpet, and the rich verdure covers the open ground where the trees are absent. Bogs and swamps take the place of arid wastes. Pines and larches are larger and larger; after a time they disappear to make way for foliferous trees. The way of the traveller is devious and full of toil; it is blocked by fallen trunks mingled in perplexing confusion, and unless he is where a road has been opened the progress of an hour is counted by feet or yards, in place of the miles left behind in the open country. Especially in the mountain ravines, where the trees have been swept down by the torrents, is the way thus obstructed. Trees and great stones are piled closely together, and sometimes they form an arch beneath which the stream meanders during the dry season. The first part of the downward journey is generally along the valley of a river flowing from the mountain, but after some thousands of feet of descent it is necessary to follow a larger stream, and cross one by one its numerous tributaries. There are fresh and great difficulties in this part of the route. After crossing a stream its bank must be ascended, sometimes almost precipitously, then a dividing ridge is traversed, and then comes the descent into the next valley. In this way the main valley is descended until the lower country is reached, where the river becomes tranquil, and suited to navigation by canoes or other craft.