On the east side of the Yellowstone, close to the margin of the river, are a few turbid springs, and mud-springs strongly impregnated with alum. The mud is yellow and contains much sulphur. These, the discoverers, Dr. Hayden and his company, called Mud-sulphur Springs. The main basin is 15 by 30 feet, and has three centres of ebullition, showing that deep in the earth are three independent orifices for the emission of heated waters. Dr. Hayden's description of the roaring spring issuing from a cavern, coincides with that given above. He called it the Grotto. Around all these springs he observed an abundance of grasses, rushes, mosses, and other plants growing with a surprising luxuriance. The recent mud-volcano described by Mr. Langford was considered by Dr. Hayden as the most remarkable mud-spring thus far discovered in the West. "It does not boil with an impulse like most of the mud-springs," he says, "but with a constant roar which shakes the ground for a considerable distance, and may be heard for half a mile. A dense column of steam is ever rising, filling the crater, but now and then a passing breeze will remove it for a moment, revealing one of the most terrific sights one could well imagine. The contents are composed of thin mud in a continual state of the most violent agitation, like an immense caldron of mush submitted to a constant, uniform, but most intense heat.... All the indications around this most remarkable caldron show that it has broken out at a recent period; that the caving in of the sides so choked up the orifice that it relieved itself, hurling the muddy contents over the living pines in the vicinity."