The tramp of our horses' feet as we rode over the incrustation at the base of the mountain returned a hollow sound; yet while some of our party were not disposed to venture upon it with their horses, still I think with care in selecting a route there is very little danger in riding over it. On the mountain, large quantities of sulphur formed by the condensation of the vapor issuing from the crevices, now closed, but once in activity in the incrusted covering, have been deposited, and we collected many specimens of pure and crystallized sulphur. Thousands of pounds of pure and nearly pure sulphur are now lying on the top and sides of the mountain, all of which can be easily gathered with the aid of a spade to detach it from the mountain side incrustations to which it adheres in the process of condensation. We gave to this mountain the name "Crater hill." Five miles further on we camped near the "Mud geyser." Our course to-day has been for the greater part over a level valley, which was plainly visible from the top of Mount Washburn. The water of the river at this point is strongly impregnated with the mineral bases of the springs surrounding our camp, and that empty into the river above it. Friday, September 2.--To-day we have occupied ourselves in examining the springs and other wonders at this point. At the base of the foot-hills adjoining our camp are three large springs of thick boiling mud, the largest of which resembles an immense cauldron. It is about thirty feet in diameter, bordered by a rim several feet wide, upon which one can stand within reach of the boiling mass of mud, the surface of which is four or five feet below the rim enclosing it, the rim being a little raised above the surrounding level. Some twelve or fifteen rods from this spring are two other springs from ten to twelve feet in diameter. Near by is a hot (not boiling) spring of sulphur, fifteen to eighteen feet in diameter, too hot to bathe in. From these we passed over the timbered hill at the base of which these springs are situated. In the timber along the brow of the hill and near its summit, and immediately under the living trees, the hot sulphur vapor and steam issue from several fissures or craters, showing that the hottest fires are raging at some point beneath the surface crust, which in a great many places gives forth a hollow sound as we pass over it. Through a little coulee on the other side of the hill runs a small stream of greenish water, which issues from a small cavern, the mouth of which is about five feet high and the same dimension in width. From the mouth, the roof of the cavern descends at an angle of about fifteen degrees, till at the distance of twenty feet from the entrance it joins the surface of the water. The bottom of the cavern under the water seems to descend at about the same angle, but as the water is in constant ebullition, we cannot determine this fact accurately. The water is thrown out in