Another kind of frozen water is the hoar frost which forms on the rock roofs and walls. This is not at all rare. It is an open question whether this is not the same thing as that which has been described as subterranean snow.[29] I found myself in Dóbsina a small sheet of what to look and touch was snow. I wrote of this as snow in my first paper about glacières[30], but I am of the opinion now that it was the hoar frost detached from the roof and not genuine snow.
[29] See Part III.: Ziegenloch, [page 247]; Creux de Souci, [page 207].
[30] Ice Caves and the Causes of Subterranean Ice, November, 1896, and March, 1897.
At Dóbsina, also, I noticed that the ice of the ice wall of the Korridor assumed a stratified or laminated form. Mr. John F. Lewis of Philadelphia suggested to me that this was probably due to a precipitation of the hoar frost from the roof, and I think his explanation is correct. The hoar frost forming at a certain degree of cold, would doubtless be precipitated at a rise of temperature, and would then act much as do the different layers of snow in the upper portion of glaciers.[31] It would consolidate gradually, layer over layer, and form strata, producing the banded or laminated structure visible in the vertical ice of the Dóbsina Korridor.
[31] Whymper: Scrambles amongst the Alps, 1871, page 426.
The ice in caverns is sometimes found with a structure which is, I believe, of rare occurrence above ground. This is when it takes the shape known as prismatic ice, which means that if a lump is broken from a column or icicle, the fracture will show regular prisms. This phenomenon is not as yet satisfactorily accounted for; the only thing certain about it is, that it does not occur in ice of recent formation. From my own observations, I should say that ice became prismatic at the end of summer; at least I have always found it in August or September rather than in June or July.[32]
[32] See Part IV.: Browne, [page 289]; Lohmann, [page 303].
Besides building up ice heaps, the drip, also, has the function of destroying its own creations. If there are no crevasses, there are holes and runnels. These are generally found at or leading to the lowest point of the ice floor. Occasionally the holes are deep, sometimes many meters in depth. They are certainly cut out by the melting water, to which they offer an exit; in fact they are a part of the drainage system present in all glacière caves, where there must be some outlet for surplus water at or near the lowest point: and as the caves are always in porous or broken rock, the drainage takes place through the cracks and fissures.
The drip produces also the exact opposite of pyramids in the shape of ice basins. These are cut in the floor by an extra strong drip from the roof at those spots. Basins exactly like these are not seen on glaciers. Not infrequently they are full of water of considerable depth.
Lakes and pools are found in glacière caves. Sometimes they are on the ice floor, and in this case they are due either to rain-water collecting faster than it can flow off, or else because the cave is in a state of thaw. Sometimes these pools are among the rocks in one part of a cave, while the ice is in another part.