Along the eastern side of this Lower Geyser Basin are several extensive areas abounding in mud-springs, boiling springs and geysers, whose infinitely varied characteristics can have no more than the briefest notice. Beginning at the north, the first that commands attention is that whose central object of interest is the Thud Geyser, so called from the peculiar noise it makes as the water rises and recedes. It is situated on the slope of a small hill, is about twenty feet in diameter, and has a crater five feet wide and five high, composed of geyserite of a greyish color, full of deep pockets containing balls of the same material, about the size of walnuts, each one covered with little rosette-like formations. The column of water thrown out by this geyser during its eruptions is very wide, and reaches the height of fifty feet. Near it was obtained some pieces of wood, coated with geyserite of a delicate pink tinge: the silica had thoroughly penetrated the woody fibre. There were found, also, pine-cones coated in the same manner, forming beautiful specimens. A few yards back of the geyser are three large mud-springs, in one of which the mud is red, in another white, and in the third pink--the jets of steam causing the mud to assume the form of small conical points throughout the basins. They are situated in a bed of clay, the red color being due to iron. Below these latter are some chalybeate springs whose bright-red iron deposit have spread over a considerable area, in glaring contrast with the white color of the silicious deposits of their neighbors. In the same group is a fissure spring forty feet long, four feet wide and ten deep, clear as crystal; also a large basin nearly circular, fifty feet in diameter with a number of huge apertures, some of which throw up water thirty feet. One orifice shoots a constant stream six feet high. All around this geyser-group are smaller springs continually bubbling, and large numbers of small geysers, some constantly playing to heights not exceeding ten feet, while others merely keep up a violent ebullition, rising and falling with a pulsating motion. There is also one beautiful quiet spring, with a basin so large that it looks like a small lake. Into its clear depths one may look down thirty or forty feet, beholding a fairy-like palace adorned with more brilliant colors than any structure made by human hands. The aggregate waters of the group form a little stream which flows westward into the small lake already noticed in connection with the mud-springs at the lower end of the basin.