Facts like these clearly demonstrate that, from a geologic standpoint, thermal activity in the Park is gradually becoming extinct; and many persons, taking alarm at this evidence, imagine that the unique phenomena of the Yellowstone are of an evanescent character, and that the time is not far remote when they will be known only as matters of history. There is, however, no occasion for such misgiving. The present condition is the result of processes that run back probably for millions of years; certainly for periods of time compared with which recorded history is insignificant. The same rate of progress would produce no perceptible change in the lifetime of an individual. Some who have visited the geyser regions more than once assert that, after an interval of several years, they observe a marked diminution in thermal activity. But this is probably because a second visit ordinarily makes a less vivid impression than a first. The weight of reliable evidence is certainly the other way. Mr. David E. Folsom, leader of the Expedition of 1869, made a tour of the Park during the present season of 1895. He says: "I had a very vivid recollection of all I saw twenty-six years ago, and I note no important change." Professor Arnold Hague, probably the best living authority upon the scientific features of the Park, has compared the hot springs and geysers by means of authentic records covering intervals of several years, and he declares that he finds "no diminution in the intensity of action or in the amount of discharge from the springs and geysers, since they have been subject to careful observation." While it is certain that springs are constantly becoming inactive, it is no less certain that others replace them, and it may be confidently assumed that the progress toward ultimate extinction will be inappreciable in our time or for many generations to come. The distribution of thermal springs over the surface of the earth is probably more general than is commonly supposed. Only one extensive area is practically without them, and that is the Continent of Australia. Africa, also, has very few. But in other parts of the globe they are found almost without number, ranging from the Equator to the Arctic Circle, and from sea-level to the lofty table lands of Thibet. The three localities, however, in which they abound in such numbers and magnitude as to attract marked attention are, in the order of their discovery, Iceland, New Zealand, and the Yellowstone National Park. In extent, variety, and magnitude of accompanying phenomena, and in geologic age, the above order is reversed. Iceland has probably the most famous geyser in the world, principally because it was for a long time the only known geyser, and consequently received a great deal of scientific attention; but judging from published descriptions it is clearly inferior to several now known in the Firehole Geyser Basin.