The most interesting exhibit of the Katmai National Monument, however, is a group of neighboring valleys just across the western divide, the principal one of which Mr. Griggs, with picturesque inaccuracy, named the "Valley of Ten Thousand Smokes"; for, from its floor and sides and the floors and sides of smaller tributary valleys, superheated steam issues in thousands of hissing columns. It is an appalling spectacle. The temperatures of this steam are extremely high; Griggs reports one instance of 432 degrees Centigrade, which would equal 948 degrees Fahrenheit; in some vents he found a higher temperature at the surface than a few feet down its throat. The very ground is hot. This phenomenal valley is not to be fully explained offhand; as Griggs says, there are many problems to work out. The steam vents appear to be very recent. They did not exist when Spurr crossed the valley in 1898, and Martin heard nothing of them when he was in the near neighborhood in 1903 and 1904. The same volcanic impulse which found its main relief in the explosive eruption of near-by Katmai in 1912 no doubt cracked the deep-lying rocks beneath this group of valleys, exposing superheated rocks to subterranean waters which forthwith turned to steam and forced these vents for escape. Griggs reports that volcanic gases mingle freely with the steam. The waters may have one or more of several sources; perhaps they come from deep springs originating in surface snows and rains; perhaps they seep in from the sea. Whatever their origin the region especially interests us as a probably early stage of phenomena whose later stages find conspicuous examples in several of our national parks. Some day, with the cooling of the region, this may become the valley of ten thousand hot springs. But it is useful and within scientific probability to carry this conception much further. The comparison between Katmai's steaming valleys and the geyser basin of Yellowstone is especially instructive because Yellowstone's basins doubtless once were what Katmai's steaming valleys are now. The "Valley of Ten Thousand Smokes" may well be a coming geyser-field of enormous size. The explanation is simple. Bunsen's geyser theory, now generally accepted, presupposes a column of water filling the geyser vent above a deep rocky superheated chamber, in which entering water is being rapidly turned into steam. When this steam becomes plentiful enough and sufficiently compressed to overcome the weight of the water in the vent, it suddenly expands and hurls the water out. That is what makes the geyser play.