Passing from this room by a long, narrow passage, in the walls of which are observed many beautiful little pockets of crystals, attention is presently called to Lincoln's Fireplace, a perfectly natural specimen of the old-fashioned design broadly open in the chimney; doubtless just such an one as Mr. Lincoln's good mother hung the crane in and set the Dutch oven before. A little beyond and on the opposite side of the crevice is Prairie-dog town, not a very extensive town, to be sure, but so true a copy that one unfamiliar with the small animal and his style of architecture would afterwards easily recognize both. At one time his dogship was carried away by a too eager collector, but a letter to the suspected visitor brought him home by the next freight. The Dutch Clock occupies a position on a shelf near by, and all southern visitors greet the Alligator as a familiar friend, as all of us joyfully meet any acquaintance from home. A long narrow passage, formerly a "tight crawl," but later opened up by heavy blasting, must be traversed before we come to the Snow Ball Room, beautiful with round spots of untinted carbonate of lime, as if fresh soft snow had been thrown by the handful over walls and ceilings, with the additional ornamentation of calcite crystals. In the crevice beyond rises the Church Steeple, diminishing regularly, though roughly, in size, to a height of sixty feet, but not degraded with the little squirming stairway usually seen in Church spires. The next room is the Post Office, in which we are for the first time introduced to the greatest peculiarity and most abundant formation known to the cave. Being a newly discovered addition to geology it has no scientific name and therefore is simply called box work, because it resembles boxes of many shapes and sizes. The formation of the box work is generally regarded as an unexplained and unexplainable mystery, but a careful study of various portions of the cave shows it in all stages of development and suggests a reasonable theory as to the cause of its origin and variety of development. The volcanic disturbances which have already been discussed as having been responsible for the various uplifts and depressions of the Black Hills region, and also for opening the fissures which gave the cave a beginning, must have supplied the conditions that were necessary to the formation of box work. And these preliminary conditions were merely cracks in the rock. By the violence of earth movement the limestone has been crushed, probably when the land was undergoing depression, prior to the upheaval which opened the great parallel fissures. The varying hardness of the rock, as well as proximity to the surface, would readily account for the difference in size of the fractures, which is from one-half inch to twelve inches; the largest being the most distant from the surface. That this crushing was done before the salt waters retired from the region, which was towards