There are five large springs and half a dozen smaller ones in this basin, all of them strongly impregnated with sulphur, alum and arsenic. The water from all the larger springs is dark brown or nearly black. The largest spring is fifteen to eighteen feet in diameter, and the water boils up like a cauldron from 18 to 30 inches, and one instinctively draws back from the edge as the hot sulphur steam rises around him. Another of the larger springs is intermittent. The smaller springs are farther up on the bank than the larger ones. The deposit of sinter bordering one of them, with the emission of steam and smoke combined, gives it a resemblance to a chimney of a miner's cabin. Around them all is an incrustation formed from the bases of the spring deposits, arsenic, alum, sulphur, etc. This incrustation is sufficiently strong in many places to bear the weight of a man, but more frequently it gave way, and from the apertures thus created hot steam issued, showing it to be dangerous to approach the edge of the springs; and it was with the greatest difficulty that I obtained specimens of the incrustation. This I finally accomplished by lying at full length upon that portion of the incrustation which yielded the least, but which was not sufficiently strong to bear my weight while I stood upright, and at imminent risk of sinking in the infernal mixture, I rolled over and over to the edge of the opening; and, with the crust slowly bending and sinking beneath me, hurriedly secured the coveted prize of black sulphur, and rolled back to a place of safety. [Illustration: SECURING A SPECIMEN AT HELL-BROTH SPRINGS.] From the springs to the mouth of the creek we followed along the bank, the bed or bottom being too rough and precipitous for us to travel in it, the total fall in the creek for the three miles being about fifteen hundred feet. Standing upon the high point at the junction of the creek with the Yellowstone, one first gets some idea of the depth of the cañon through which the river runs. From this height the sound of the waters of the Yellowstone, tumbling over tremendous rocks and boulders, could not be heard. Everything around us--mountains, valleys, cañon and trees, heights and depths--all are in such keeping and proportion that all our estimates of distances are far below the real truth. To-day we passed the mouth of Hell-Roaring river on the opposite side of the Yellowstone.