:
the current had reversed. Soon after this the hole was enlarged to
eighteen by thirty inches and the cave entered by quite a number of
venturesome persons assisted by a long rope and ample personal courage.
No other improvements were made, and only a short distance was explored,
until Mr. J.D. McDonald settled on the property in 1890; since which
time he and his sons have explored ninety-seven miles of passage and
done such extensive work in opening up small passages and placing
ladders, that it is now possible for visitors to travel long distances
with surprising ease and comfort. The measure of distances in the cave
is not by the usual guess-work method which has established the
short-measure reputation for cave miles, but is done with a fair degree
of accuracy by means of the twine used to mark the trail in exploring
new passages. A careful measurement of the twine has shown it to run
nine balls to the mile with a close average of regularity, so it is the
custom to add another mile to the cave record as often as a ninth ball
becomes exhausted.

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 solubl