In the game pocket of your coat stow a lunch and an emergency ration, along with the small canteen of water. Somebody should carry a cup, as you may have to catch drip-water. Let another man bear a cold-chisel and a small hammer for collecting specimens, marking passages, and cutting nicks for handhold and foothold. If there is any likelihood of descending into a lower gallery, take about fifty feet of Alpine rope (to be had of some camp outfitters).
Large cavern chambers cannot be illuminated with lanterns. So go provided with strips of magnesium ribbon. Do not try to use this ribbon as a substitute for flash-powder in photographing: it will show the most freakish bolts of lightning in your pictures. Satisfactory interiors, in caves, can only be taken with a wide-angle lens, as the range is nearly always short.
In estimating distances beware of "cave miles." It is almost impossible to keep from overestimating distances in labyrinths um derground, unless one trails a cord behind him wherever he goes. A cave mile, when tried by tape-line, generally proves to be only a few hundred yards long. Heights, depths, and widths are also very deceptive by lantern light.
It may be asked, How are heights of cavern domes measured? They used to be "measured" by timing the flight of rockets made for the purpose, but such expedients were very inaccurate. The only easy and reliable way that I know of is by sending up toy balloons with cord attached. There are no draughts in the interior of caves, and this method can be depended on, no matter how high the vault may be.
Do not be afraid of fire-damp, unless you are going down a sink-hole that may have been sealed at the bottom. The air of a true cave is purer and more invigorating than any to be breathed on earth. One can work with less fatigue in a cave than in the open air.
The chance of finding caverns that no one else has explored is now limited, in our country, mostly to those that can be entered by descending sinkholes. This is work that calls for deliberate preparation and cool heads. After effecting an opening in the bottom of the 'sink," if it has been closed, erect a strong frame over the opening to hold a hoisting-tackle, and use a rope which has been stretched enough to insure that it will not spin round when a weight is suspended from it. This rig is better than a windlass, if for no other reason than that the explorer has more confidence that it will not let fly and drop him. For short descents it is sufficient to fasten the rope around the left ankle of the adventurer and then make a stirrup-loop for his foot. Generally it is better to rig a boatswain's chair to sit in (Fig. 149). This is simply a board seat with an auger-hole at each end through which a slack rope is roved and the ends knotted, after which the hoisting rope is made fast to the middle of the slack at a convenient height.
Before a man starts down he fastens a signal cord to his waist, which is then passed to one side of the opening, where it cannot become entangled with the hoisting rope, and is managed there by somebody who has no other duty to distract him. One jerk on this cord means stop, two, lower, three hoist. Such an appliance is absolutely necessary in deep holes, unless some sort of telephone is substituted. There should be three trusty men for the main rope and one for the signal-cord. The explorer should have a staff to help him swing clear of impediments, and it must be tied to him by a lanyard.
Before the descent is made all loose stones should be removed from around the mouth of the pit, for a pebble falling from a considerable height may stun or kill a man. A ball of something like cotton waste, saturated with oil, should be ignited and dropped into the pit before descending, to guard against accident from fire-damp.
The chief commerv cial product of caves, up to date, is the so-called "Mexican Onyx," which is a fine-grained, translucent, and beautifully colored variety of dripstone. Occasionally the "cave pearls" found in shallow pools, where they have been polished by attrition, have been set as gems. In olden times nearly all the niter used by our forefathers in making gun^ powder was procured from caverns. Guano, ochre, and the sulphates of soda and of magnesia are found in caves. The chance of discovering mineral veins is lessened by the incrustation of dripstone that coats the walls; there is no "bloom" to attract the eye.
The animal life of caverns is peculiar. It includes transparent fish, white crayfish, cave lizards, white mice and rats, cave crickets, and minor species —all blind, and some of them quite eyeless—besides the usual colonies of bats. Snakes are never met inside of caverns, but sometimes may be encountered in sink-holes, or in the "rock-houses" previously mentioned.
Digging in the floors of caves for relics of prehistoric man has long been a favorite branch of science in Europe, but comparatively little of this wrork has been done in America. Sometimes human skeletons of our own era are found encased in the dripstone, as at Luray, at Mammoth Cave, in the Adelsberg, and in the Cave of Melidoni, where the remains of three hundred Cretans, who were -smoked to death by the Turks in 1822, are gradually disappearing in a stony shroud.