The dreams and fasts of the Dakotas, and the time passed by them in solitude, explain much that is strange and exceptional in their nature. It is thus intelligible how it happens, that the young Indians have such an earnest and vivid belief in the spiritual nature of the unknown and mysterious world, and that they invest with supernatural attributes the mysterious powers which surround them. It must seem natural to them, that thunder and lightning, sun, moon, mountains, and rivers, should be considered as manifestations of powerful spirits, that require to receive worship and sacrifice. What, however, is not so obvious, is the cause which impels them to worship large rocks and stones, which cannot, by any stretch of the imagination, be supposed to possess active powers of good or evil. Upon this subject I asked the Indians for their explanation, saying, that I supposed they did not directly worship a stone, such as that near Mendota, but the spirit who had placed it there. Faribault said, that this worship also followed upon dreams, and the Indians, who were present, concurred in his statement. It sometimes happens that a Sioux, in his dream, instead of seeing the image of the sun or some animal, will see nothing but one of these large Spirit rocks. It is thus conveyed to his mind, that this is his god, by which his actions and fate are to be governed during his life, and to whom he must offer sacrifices. The whole tribe will occasionally take part in the worship of a boulder.[49] A dreamer, usually in this case, a man who is supposed to be gifted with prophetic power, dreams that it has become necessary to propitiate some unknown spirit. Then if he afterwards dreams of one of these boulders he acquaints the tribe with the nature of his dream, and the camp is immediately moved to the neighbourhood of the particular stone that is to receive sacrifices. This worship of Spirit rocks continues to take place. There is a large rounded mass of granite on the west bank of the Mississippi, lying upon the prairie a few miles below Lake Pepin, which is still visited by wandering bands of Sioux. It had been painted a bright red colour. When passing near the spot where it was situated, I saw the fires of the encampment of Indians who had come there to perform their ceremonies.