"April 8.--The river-banks exhibit indications of volcanic agency. The bluffs which we passed to-day are upwards of one hundred feet high, composed of yellow clay and sand, with horizontal strata of carbonated wood resembling pit-coal, from one to five feet in thickness, scattered through the bluff at different elevations. Great quantities of pumice-stone and lava are seen in many parts of the hills, where they are broken and washed into gullies by the rain. We passed a bluff which is on fire, and throws out quantities of smoke, which has a strong, sulphurous smell. On the sides of the hills is a white substance, which appears in considerable quantities on the surface, and tastes like a mixture of common salt with Glauber salts. Many of the springs which come from the foot of the hills are so impregnated with this substance, that the water has an unpleasant taste, and a purgative effect." THE PRAIRIE-MICE. "April, 1805.--We saw, but could not procure, an animal that burrows in the ground, similar to the burrowing-squirrel, except that it is only one-third of its size. This may be the animal whose works we have often seen in the plains and prairies. They consist of a little hillock of ten or twelve pounds of loose earth, which would seem to have been reversed from a flower-pot; and no aperture is seen in the ground from which it could have been brought. On removing gently the earth, you discover that the soil has been broken in a circle of about an inch and a half in diameter, where the ground is looser, though still no opening is perceptible. When we stopped for dinner, the Indian woman went out, and, penetrating with a sharp stick the holes of the mice, brought a quantity of wild artichokes, which the mice collect, and hoard in large quantities. The root is white, of an ovate form, from one to three inches long, and generally of the size of a man's finger; and two, four, and sometimes six roots are attached to a single stalk. Its flavor, as well as the stalk that issues from it, resemble those of the Jerusalem artichoke, except that the latter is much larger." THE YELLOW-STONE RIVER. "Certain signs, known to the hunters, induced them to believe that we were at no great distance from the Yellow-stone River. In order to prevent delay, Capt. Lewis determined to go on by land in search of that river, and make the necessary observations, so as to enable us to proceed immediately after the boats should join him. "On leaving the party, he pursued his route along the foot of the hills; ascending which, the wide plains watered by the Missouri and the Yellow-stone spread themselves before his eye, occasionally varied with the wood of the banks, enlivened by the windings of the two rivers, and animated by vast herds of buffaloes, deer, elk, and antelope." NATURAL HISTORY.