"By its contact with the air the water is cooled, falls back into the basin, partially refills the tube, in which it gradually rises, and finally fills the basin as before. Detonations are heard at intervals, and risings of the water in the basin. These are so many futile attempts at an eruption, for not until the water in the tube comes sufficiently near its boiling temperature, to make the lifting of the column effective, can we have a true eruption." The principal geyser regions of the world are in Iceland, in New Zealand, and in the Yellowstone National Park in the United States. There are several geyser regions in Iceland. The best known lies in the neighborhood of Mt. Hecla. Here is a great geyser that shoots up a column of water to a height of about 100 feet every thirty hours. Fig. 35 represents the appearance of the crater of the great geyser in Iceland. [Illustration: FIG. 35. CRATER OF THE GREAT GEYSER OF ICELAND] It is a well-known fact that in geyser regions generally, the throwing of stones or other materials into the tube will frequently hasten an eruption. This is probably due to the fact that the throwing in of these things results in the raising of the water in the tube, thus hastening the eruption. The New Zealand region is in the neighborhood of Lake Rotomahama in the northern island. The geyser region in the Yellowstone Park is by far the most interesting of all geyser regions. This region is situated principally around Fire-Hole Fork of the Madison, and near Shoshone Lake at the head of Lake Fork of the Snake River. There are many geysers in this region, as well as simple hot springs. The temperature of their waters varies from between 160° and 200° F. to the boiling point of water at this elevation. As you are probably aware, water boils at the temperature of 212° F. only under the condition of the ordinary atmospheric pressure that exists at the level of the sea. At higher elevations, such as on the slopes of mountains, or on high plateaus, water boils at a lower temperature. The height of the country in which the Yellowstone Park is situated is so great that the water boils at temperatures of from 198° to 199° F. The conical hillock of geyser cones from which the waters flow assume various shapes, two of which are shown in Figs. 36 and 37. [Illustration: FIG. 36. GIANT GEYSER _From Dana's Manual of Geology_] [Illustration: FIG. 37. BEE HIVE _From Dana's Manual of Geology_] That shown in Fig. 36 represents the shape of the cone of the giant geyser in the upper geyser basin of the Fire-Hole, Yellowstone National Park. This cone is about ten feet in height, and twenty-four feet in diameter. As shown in the figure it is broken on one of its sides. It throws out, at long intervals, a column of water the height of which varies from ninety to 200 feet. Fig. 38 represents the crater of a cone known as the Bee Hive in eruption.