The quiescent spring seems to stand at the opposite pole from the geyser. The conditions are such that the water nowhere reaches a temperature sensibly above the boiling point. The surface therefore steams quietly away, unruffled except by the passing breeze. The great attraction of these springs is in the inimitable coloring of the water. It is not simply the beautiful green or blue of great depths of clear water. In no ordinary pool can one find all the colors of the spectrum, flitting about, as though seen through a revolving prism. Sometimes there is an iridescent effect similar to that of a film of oil upon water; but there is no oil here. There are doubtless many contributing causes that produce these remarkable effects. There is first a great depth of clear water which always presents a beautiful appearance. Then there are the mineral deposits on the sides of the crater, producing indefinite reflection, the effects of which are multiplied by the refractive power of the water. The mineral ingredients dissolved or suspended in the water doubtless add to the effect. The hot springs on the Gardiner River are wholly different in character from those in any other part of the Park. The water of these springs holds carbonate of lime in solution while most of the others contain silica. To this fact must be attributed the peculiar character of the formations at Mammoth Hot Springs. Wherever the deposits of springs are calcareous, the character of the formations is the same, and generally different from those produced by the deposit of silica. They rise in terraces one above another, and mold for themselves overhanging bowls of transcendent beauty in form and color. In the tints displayed by the water, however, these springs are not unlike others in the Park. [Illustration: _Terry Engr. Co._ _Haynes, Photo., St. Paul._ Cleopatra Terrace.] The rims about the quiescent springs are often very beautiful, and the observer is astonished to see how they stand up above the general surface of the ground so evenly built that the water has hardly a choice of route in flowing away. Tyndall, however, makes this puzzling phenomenon clear. He says: "Imagine the case of a simple thermal siliceous spring, whose waters trickle down a gentle incline; the water thus exposed evaporates speedily, and silica is deposited. This deposit gradually elevates the side over which the water passes, until finally the latter has to take another course. The same takes place here; the ground is elevated as before, and the spring has to move forward. Thus it is compelled to travel round and round, discharging its silica and deepening the shaft in which it dwells, until finally, in the course of ages, the simple spring has produced that wonderful apparatus which has so long puzzled and astonished both the traveler and the philosopher."