Forest fires, where there is opportunity, sweep up the mountain-side against the lower side of the trees. The lower side is thus often scarred while the opposite side is scarcely injured; but wind blowing down the gulch at the time of each fire may have directed the flames against the lower side of this tree. In many places clusters of young trees were growing close to the lower side of the old trees, and were enabled to grow there by light that came in from the side. It may be that the heat from one of the blazing clusters scarred this old pine; then another young cluster may have grown, to be in time also consumed. But these scars may have resulted, wholly or in part, from other causes. Yellow pine claims the major portion of the well-drained slopes, except those that are northerly, in the middle mountain-zone up to the lower lodge-pole margin. A few groves are found higher than nine thousand feet. Douglas spruce covers many of the northerly slopes that lie between six thousand and nine thousand feet. The regularity of tree-distribution over the mountains is to me a never-failing source of interest. Though the various species of trees appear to be growing almost at random, yet each species shows a decided preference for peculiar altitude, soil, temperature, and moisture conditions. It is an interesting demonstration of tree adaptability to follow a stream which comes out of the west, in the middle mountain-zone, and observe how unlike the trees are which thrive on opposite sides. On the southerly slopes that come down to the water is an open forest of yellow pine, and on the opposite side, the south bank, a dense forest of Douglas spruce. If one be told the altitude, the slope, and the moisture conditions of a place on the Rockies, he should, if acquainted with the Rockies, be able to name the kinds of trees growing there. Some trees grow only in moist places, others only in dry places, some never below or above a certain altitude. Indeed, so regular is the tree-distribution over the Rockies that I feel certain, if I were to awaken from a Rip Van Winkle sleep in the forests on the middle or upper slopes of these mountains, I could, after examining a few of the trees around me, tell the points of the compass, the altitude above sea-level, and the season of the year. [Illustration: ASPENS]