How long it took each growth to reach maturity; how long it flourished afterward before destruction; and how long the several lava flows suspended vegetable growth; are matters largely conjectural. But at the very lowest estimate the time represented by these various accumulations can not be less than five thousand years. That these early trees were of a different species from those which now flourish there, need not excite surprise, for climatic and other conditions are wholly changed. But an equal difference seems also to have prevailed between the successive growths, the trees of which were not only unlike each other, but nearly all were of species hitherto unknown to science. Fortunately the rare perfection of some of the specimens, particularly of the leaves and bark, have greatly simplified their classification, and have given valuable clues to their geologic age. The products of these petrifactions in time strewed the surface of the ground with such an abundance of specimens as to give the locality its present name. Most of the lighter specimens, and some of the heavier, have been carried away. Besides the general interest of these old forests to the casual observer, they are of great value to science, for probably in no other part of the globe can a similar chapter of its history be found more clearly recorded. CHAPTER VI. FAUNA OF THE YELLOWSTONE. The universal curiosity of people to see what are popularly called wild animals, especially those larger species which never frequent the precincts of civilization, is a fact of which it is not easy to give a philosophical explanation. In this country the rapid disappearance, amounting almost to annihilation, of the large game is looked upon as a great misfortune; and in later years there has arisen a fixed purpose that protection shall be secured for the surviving remnants of those species which once with the red man held possession of the continent. The statutes of nearly every state give evidence of the universality of this sentiment. As a means of accomplishing such a purpose, no institution promises to be more effectual than the Yellowstone Park. It ought, in this respect, to be a complete realization of Catlin's dream. Its importance as a game preserve was recognized in the Act of Dedication, and has become more and more pronounced as acquaintance with it has increased. The Park is fortunately better adapted for this purpose than any other tract of similar extent in America. It offers very little to tempt the cupidity of man. Its mineral wealth is buried so deeply under the lava that no miner will ever reach it. Its altitude and climate unfit it for agriculture. Its forests, though excellent for shade, are of little value for lumber. But as a home for the native species of the continent, it possesses unrivaled advantages. These are admirably summed up in the following paragraph from the pen of Prof. Hague: [Illustration: _Terry Engr. Co._ _Haynes, Photo., St. Paul._