Another old burn visited was a small one in an Engelmann spruce forest on a moderate northern slope. It had been stopped while burning in very inflammable timber. It is probable that on this occasion either a rain or snow had saved the surrounding forest. The regrowth had slowly extended from the margin of the forest to the centre of the burn until it was restocked. One morning I noticed two small fires a few miles down the mountain and went to examine them. Both were two days old, and both had started from unextinguished camp-fires. One had burned over about an acre and the other about four times that area. If the smaller had not been built against an old snag it probably would have gone out within a few hours after the congressman who built it moved camp. It was wind-sheltered and the blaze had traveled slowly in all directions and burned a ragged circle that was about sixty feet across. The outline of the other blaze was that of a flattened ellipse, like the orbit of many a wandering comet in the sky. This had gone before the wind, and the windward end of its orbit closely encircled the place of origin. The camp-fire nucleus of this blaze had also been built in the wrong place,--against a fallen log which lay in a deep bed of decaying needles. Of course each departing camper should put out his camp-fire. However, a camp-fire built on a humus-covered forest floor, or by a log, or against a dead tree, is one that is very difficult to extinguish. With the best of intentions one may deluge such a fire with water without destroying its potency. A fire thus secreted appears, like a lie, to have a spark of immortality in it. A fire should not be built in contact with substances that will burn, for such fuel will prolong the fire's life and may lead it far into the forest. There is but little danger to the forest from a fire that is built upon rock, earth, sand, or gravel. A fire so built is isolated and it usually dies an early natural death. Such a fire--one built in a safe and sane place--is easily extinguished. The larger of these two incipient fires was burning quietly, and that night I camped within its orbit. Toward morning the wind began to blow, this slow-burning surface fire began to leap, and before long it was a crown fire, traveling rapidly among the tree-tops. It swiftly expanded into an enormous delta of flame. At noon I looked back and down upon it from a mountain-top, and it had advanced about three miles into a primeval forest sea, giving off more smoke than a volcano. I went a day's journey and met a big fire that was coming aggressively forward against the wind. It was burning a crowded, stunted growth of forest that stood in a deep litter carpet. The smoke, which flowed freely from it, was distinctly ashen green; this expanded and maintained in the sky a smoky sheet that was several miles in length.