The forest is incessantly aggressive and eternally vigilant to hold its territory and to advance. Winds are its most terrible and effective foe. To them is due its weird and picturesque front. Occasionally they rage for days without cessation, blowing constantly from the same quarter and at times with the rending and crushing velocity of more than one hundred miles an hour. These terrific winds frequently flay the trees with cutting blasts of sand. At times the wind rolls down the steeps with the crushing, flattening force of a tidal wave. Many places have the appearance of having been gone over by a terrible harrow or an enormous roller. In some localities all the trees, except the few protected by rocky ledges or closely braced by their encircling fellows, are crippled or overthrown. [Illustration: THE WAY OF THE WIND AT TIMBER-LINE] Although I have visited timber-line in a number of States, most of my studies have been made on the eastern slope of the Continental Divide in Colorado. This ragged edge, with its ups and downs and curves, I have eagerly followed for hundreds of miles. Exploring this during every month of the year, I have had great days and nights along the timber-line. It was ever good to be with these trees in the clear air, up close to the wide and silent sky. Adventurers they appeared, strangely wrapped and enveloped in the shifting fog of low-drifting clouds. In the twilight they were always groups and forms of friendly figures, while by moonlight they were just a romantic camp of fraternal explorers. Many a camp-fire I have had in the alpine outskirts of the forest. I remember especially one night, when I camped alone where pioneer trees, rusty cliffs, a wild lake-shore, and a subdued, far-off waterfall furnished sights and sounds as wild as though man had not yet appeared on earth. This night, for a time, a cave man directed my imagination, and it ran riot in primeval fields. After indulging these prehistoric visions, I made a great camp-fire with a monumental pile of tree-trunks and limbs on the shore of the lake, close to the cliff. These slow-grown woods were full of pitch, and the fire was of such blazing proportions that it would have caused consternation anywhere in Europe. The leaping, eager flames threw wavering lights across the lake on the steeply rising heights beyond. These brought the alarm cry of a coyote, with many an answer and echo, and the mocking laughter of a fox. Even these wild voices in the primeval night were neither so strange nor so eloquent as the storm-made and resolute tree-forms that rose, peered, and vanished where my firelight fell and changed.