The dimensions of glacière caves vary greatly. Some are large, others are small. Saint Georges, a roofed pit cave, is some twenty-five meters by twelve meters, with a depth of about twelve meters. Chaux-les-Passavant, a cave at the end of a pit tunnel, has a diameter of some twenty-seven meters. The measures of Dóbsina, a cave at the bottom of a cliff, are given as follows: Height of roof above ice floor, 10 to 11 meters; length 120 meters; breadth, 35 to 60 meters, and surface about 4644 meters. The Frauenmauerhöhle is a gallery about one hundred meters long before the ice floor is reached, and this is some fifty meters more in length by about seven meters in width. The glacière cave near Frain, on the contrary, is so small that one can only crawl in some two or three meters. In fact, glacière caves vary in size between great halls and little tunnels where one cannot stand up straight. The entrances of glacière caves also vary greatly in their dimensions. For instance, the Friedrichsteinerhöhle is on one side of a huge pit and is as large and deep as the pit. Saint Georges, on the contrary, has, near one end of the roof, a couple of holes, some three meters in diameter. The entrance to the Schafloch is four meters wide by four meters seventy centimeters high, while the entrance to Roth is not over one meter each way. A classification of subterranean ice formations, and one which applies to all the different forms, is into permanent and periodic glacières. When in any underground spot, ice remains throughout the year, the place may be called a permanent glacière; when on the contrary the ice melts away for part of the year, the place may be called a periodic glacière. This classification, which several observers have used already, is convenient and valuable. _Movements of Air._--Another classification of glacières can be made in accordance with the movements of air underground. Glacières may be divided into those where there are no strong draughts in summer and those where there are draughts: or into "apparently static caves"; and "dynamic caves" or "windholes." The first class includes those caves where there is one or more openings close together and those above the body of the cave. In such hollows the air in summer is nearly still, while in winter there are distinct rotary movements of the air as soon as the temperature outside is lower than that within. Almost all glacière caves belong to this class of caves without strong draughts in summer. Sometimes, however, ice is found in hollows where there are two or more openings, at different altitudes and at different ends of the hollow, and where there are draughts. Occasionally, also, there are fissures in the sides or rear of apparently static caves, which allow something like draughts at times, as is the case at the Grand Cave de Montarquis.