Returning to the river and crossing we find at the water's edge, nearly opposite the Grotto, the Riverside Geyser, and a short distance below, on the same side, is the Fan. The latter geyser has a double orifice, which discharges five radiating jets to the height of sixty feet, the falling drops and spray giving the appearance of a feather fan. The effect is very beautiful. Its eruptions are frequent, lasting usually from ten to thirty minutes. A vent connected with it, about forty feet distant, expels dense masses of vapor fifty or sixty feet high, accompanied by loud, sharp reports, during the time the geyser is in action. Lieutenant Doane describes the curious action of these vents as follows: "First the steam would rush from the upper crater, roaring violently, then this would suddenly cease, to be followed by a fan-like jet of water rising from the lower crater to the height of over forty feet, playing for perhaps two minutes; then this would suddenly stop flowing, and the steam would rush forth again for a time. Occasionally the small crater threw a transverse stream, alternating with the others; and thus they played on for hours, after which all would subside to a gentle bubbling." [Illustration: FAN GEYSER.] Along both banks of the river are small craters built up in every conceivable shape. Several streams pour out cascades from round holes in the rocky bank of the river, and all around are little geysers playing at intervals from six to forty feet. A plateau opposite the Fan contains fifteen hot springs of various characteristics; some are of a deep blue color and have fantastic caverns distinctly visible below the surface of the water. The openings at the surface are often beautifully edged with delicately wrought rock fringes. One variety deposits a red or brown leathery substance, partially adhering to the sides and bottom of the cavern and waving to and fro like water plants. In size these springs vary from five to forty feet in diameter. Two hundred yards below the Fan are two lively geysers called the Sentinels. The one on the right bank of the stream is in constant agitation, its waters revolving horizontally with great violence, occasionally spouting upward to the height of twenty feet, with a lateral projection of fifty feet. Much steam is thrown off at each eruption. The crater of this geyser is three feet by ten. The companion Sentinel on the other side of the stream is smaller and less active. At this point the river-valley is narrow and the stream rapid, with a considerable fall. Forty or fifty comparatively unimportant geysers and boiling springs are scattered along the narrow valley to the junction of Iron Spring Creek, the lower limit of the Upper Geyser Basin.