Wednesday, August 31.--This has been a "red-letter" day with me, and one which I shall not soon forget, for my mind is clogged and my memory confused by what I have to-day seen. General Washburn and Mr. Hedges are sitting near me, writing, and we have an understanding that we will compare our notes when finished. We are all overwhelmed with astonishment and wonder at what we have seen, and we feel that we have been near the very presence of the Almighty. General Washburn has just quoted from the psalm: "When I behold the work of Thy hands, what is man that Thou art mindful of him!" My own mind is so confused that I hardly know where to commence in making a clear record of what is at this moment floating past my mental vision. I cannot confine myself to a bare description of the falls of the Yellowstone alone, for these two great cataracts are but one feature in a scene composed of so many of the elements of grandeur and sublimity, that I almost despair of giving to those who on our return home will listen to a recital of our adventures, the faintest conception of it. The immense cañon or gorge of rocks through which the river descends, perhaps more than the falls, is calculated to fill the observer with feelings of mingled awe and terror. This chasm is seemingly about thirty miles in length. Commencing above the upper fall, it attains a depth of two hundred feet where that takes its plunge, and in the distance of half a mile from that point to the verge of the lower fall, it rapidly descends with the river between walls of rock nearly six hundred feet in vertical height, to which three hundred and twenty feet are added by the fall. Below this the wall lines marked by the descent of the river grow in height with incredible distinctness, until they are probably two thousand feet above the water. There is a difference of nearly three thousand feet in altitude between the surface of the river at the upper fall and the foot of the cañon. Opposite Mount Washburn the cañon must be more than half a vertical mile in depth. As it is impossible to explore the entire cañon, we are unable to tell whether the course of the river through it is broken by other and larger cataracts than the two we have seen, or whether its continuous descent alone has produced the enormous depth to which it has attained. Rumors of falls a thousand feet in height have often reached us before we made this visit. At all points where we approached the edge of the cañon the river was descending with fearful momentum through it, and the rapids and foam from the dizzy summit of the rock overhanging the lower fall, and especially from points farther down the cañon, were so terrible to behold, that none of our company could venture the experiment in any other manner than by lying prone upon the rock, to gaze into its awful depths; depths so amazing that the sound of the rapids in their course over immense boulders, and lashing in fury the base of the rocks on