The weather being perfect after a rain the day before, there was no need of haste to get indoors, so we lingered into the afternoon and then drove to the Mammoth Spring, in Arkansas, a short distance south of the Missouri state line, where the Cave River, just visited, comes to the surface in a bounding spring of great force. The distance being little less than nine miles. The basin filled by the Spring might be called a lake, as its size of two hundred by three hundred feet gives it that appearance, and the color is a remarkable deep blue. The volume of water is so nearly uniform that the height seldom varies more than two or three inches, but three years ago a storm of unusual violence carried out most of the native fish, and in restocking from Government supplies, the clear, cold water suggested an experiment with mountain trout which are found to be doing well. Where Mammoth Spring flows out its power is utilized by a flour mill on one bank and a cotton mill on the other, and the water flowing on forms Spring River, well known for the charm of its beautiful scenery. This Spring is described by Dr. David Dale Owen in his First Report of a Geological Reconnoissance of the northern counties of Arkansas, 1857 and 1858, pp. 60-61. CHAPTER VIII. THE BLACK HILLS AND BAD LANDS. In order to thoroughly appreciate and enjoy the wonderful caves of South Dakota, which are found within the limits of the Black Hills, it is necessary to have some knowledge of the geological character and history of that peculiar region. Prof. J.E. Todd, State Geologist, in his "Preliminary Report on the Geology of South Dakota," gives an interesting "Historical Sketch of Explorations" in his state, beginning with the expedition of Captains Lewis and Clark to the upper Missouri regions in 1804-6 to explore that portion of the recent Louisiana Purchase for the government and notify the Indians of the transfer; and including all other important expeditions since that time down to his own official tour of the Black Hills and Bad Lands in 1894. His own descriptions are so concise and graphic as to invite quotation. Of the Hills he says: