Wind Cave is twelve miles north of Hot Springs by a good road which offers somewhat meager attractions to the artist, but is more liberal towards the geologist, and especially so in fine exposures of the gypsum bearing Red Beds of the Triassic.  Limited patches of it are also exposed in each of the caves, generally carrying small quantities of selenite, which is crystallized gypsum, or in other words, crystallized sulphate of lime.  This brilliant red color is so prominent in portions of the Hills, and attracts so much wondering attention in other well known regions of the West, that it would seem an unpardonable neglect of opportunity should we fail to again quote Prof.  Todd for an explanation of the cause of the vivid coloring.  Commencing he says:  “Newton remarks concerning this:[4] ’A large percentage of peroxide of iron in the red beds, to which they owe their bright red color, bears an interesting relation to the absence of fossils.  The material of which sediments are formed is derived, by the various processes of denudation, from the rocks of older land surfaces.  Whatever iron they contain is dissolved from the land and transported in a condition of protoxide and some proto salt, such as the carbonate, and the process is facilitated by the presence of carbonic acid in the water.  Now iron occurs in these older rocks as protoxide and peroxide, the former of which is soluble and the latter insoluble in water.  The peroxide, however, by the action of organic matter, such as is held in solution in boggy waters, may be deprived of a portion of its oxygen and converted into protoxide and thus be rendered soluble.  If the iron-bearing water is confined first in a shallow basin and exposed long to the action of the atmosphere the protoxide of iron absorbs the oxygen and is precipitated as an insoluble red peroxide of iron.  If, however, plant or animal life be present in sufficient quantities, this oxidation is prevented.  In case but little foreign material, clay or sand, has been brought by the waters, the deposit will be an iron ore.  In case large quantities of foreign material are deposited from the waters at the same time, there will be produced, in the absence of life, a brown or red clay or sandstone, and in its presence a white or light colored formation containing the iron as a carbonate.  We reason therefore from the condition in which the iron is found in the red beds, that there could have been little or no life, animal or vegetable, in the water from which it was deposited.  The conclusion is strengthened by the fact of the large quantities of gypsum which are usually derived from the evaporation of saline waters.  The degree of saline concentration which the precipitation of gypsum indicates, would be highly inimical to life.  The presence of gypsum helps to account for the absence of life, and the absence of life accounts for the brilliant color.  The three prominent characteristics of the formation (that is the red beds) are therefore quite in harmony with each other.’” (Geol.  Blk.  Hills, p. 138.)