But the country is not only rugged and mountain-spurred; it possesses curiosities even greater beneath the surface than those which diversify the sun-kissed landscape over which we have just passed. On Elk Creek, and entered from the cañon wall, is Keith’s Crystal Cave, a colossal rent in the mountain bowels, with passages fifteen miles in length. It is beautifully chambered, from which depend the most exquisite crystallizations in the form of stalactites and stalagmites that reflect the torchlight in glorious colors, dancing from column of onyx to pools of pellucid water. But a more remarkable cave than Keith’s is found a little way west of Custer, and twelve miles north of Hot Springs. This marvelous natural excavation is ramified by many passages which have been explored for a distance of sixty-five miles, and the end is not yet. On account of the peculiar respiration of the cave, the air at one time rushing in with great velocity and again being expelled with equal force, it is called the Wind Cave; and no better name can be bestowed, for the cause of this inrushing and regurgitation of air seems to be beyond ascertainment. Like its more northerly cousin, Wind Cave is chambered and adorned with beautiful crystals that shimmer under the glances of the torch and are set aflame with color, with here and there such graceful formations as to suggest studios of monster sculptors. [Illustration: BEECHER ROCKS, NEAR CUSTER CITY.] ------------------------------------------------------------------------ [Illustration: A CHAMBER IN CRYSTAL CAVE, BLACK HILLS.—This wonderful subterraneous chamber is becoming more celebrated in many respects than the famous Mammoth Cave of Kentucky, beautifully photographed and described in later numbers of this work. Crystal Cave has been explored for a distance of sixty-five miles, and the end is not yet discovered. It has a marked peculiarity in its regular respiration or breathing, like a living thing; the air at stated intervals rushes in with great velocity, and is again expelled with equal force. Its chambers are halls of stalactitic splendors, almost rivaling those of the Luray Caverns. ] ------------------------------------------------------------------------ [Illustration: THE CHANCEL, CRYSTAL CAVE, BLACK HILLS.]