The desire for novel adventure which urges the members of the Alpine Club up the sides of virgin mountains, has led Mr. Browne to acquaint himself with eternal ice in the dark recesses of natural glacières, where more gains to science may be expected, and less danger to limb demanded.
Very little was known about natural ice-caves, except that they did exist. The little that was known Mr. Browne made himself acquainted with, and then set out on his tour of examination of twelve glacicres, the localities of which he had succeeded in discovering. The general reader will end his narrative full of interesting adventure, and lively description of the scenes through which he passed, as well as of the wonders he found in the caves. For the man of science they contain many interesting facts and puzzling phenomena which must rest some time before they can be thoroughly understood and expounded.
Ice-caves occur at depths varying from 50 to 200 feet below the surface of the earth, unconnected with glaciers or snow-mountains, and in latitudes and at altitudes where ice would not under ordinary circumstances be supposed to exist. They are employed, when the artificial stores of ice are exhausted, to supply this now almost necessary luxury. The ice is sometimes opaque, but frequently perfectly clear and transparent, and often formed into masses of the most beautiful or the most grotesque forms. We do not wonder that Mr. Browne, even with benumbed fingers and wet feet, crawling on all-fours on slippery ice, gets occasionally into raptures with the wondrous scene suddenly revealed to his view bythe light of his torch.
The great difficulty with regard to these ice-caves or glacieres, is to account for their existence. Our author, after recounting the numerous-many of them most absurd-theories which have been offered in explanation, gives one which to our miml is as unsatisfactory as any of the rest. It is, as he tells us, that of Deluce's, but arrived at by himself independently. He thus states it:‘ The heavy cold air of winter sinks down into the glacieres, and the lighter warm air of summer cannot on ordinary principles of gravitation dislodge it, so that heat is very slowly spread in the caves; and even when some amount of heat does reach the ice, the latter ' melts but slowly, for ice absorbs 60° C. of heat in melting; and thus, when ice is once formed, it becomes a material guarantee for the permanence of ice in the cave.
We doubt if the air is so stable a body as this theory demands. Its power of conducting heat is also considerable. It is true that the air is always cold in thc caves; but this is easily explained by the generally wet surface of the ice, which in melting absorbs so much heat. May not the earth rather than the air be the cause of the ice in the caves? There are different temperature-layers in the earth's crust, as they are erected by external heat. First, there is the thin surface-layer, affected by the varying temperature of day and night. Then there is the season temperature plane, varying with the uniformity of the seasons and the conducting power of the materials of the crust, being at the Equator only a foot below the surface, in the Arctic regions from 3 to 12, while in the Temperate Zone it is 50 or 60 feet. Then there is the layer of climate temperature, where the summer's heat and the wiuter's cold are alike unfelt; in the Temperate Zone this varies from 200 to 400 feet, and in the Arctic regions from 8 or l0 to 90. Below this we have a plane of terrestrial temperature beyond the reach of external influences.
It would be interesting to know the relation of the ico-caves to their dilferent planes of temperature. If they occur in regions where the winter is long or very severe, and the summer short or very mild, and at such a distance from the surface that seasonal changes do not affect them, then it is quite easy to understand how icc would be found in them. It would be well if explorers would direct their attention a little'to this matter. The prismatic structure of the ice, so common in the glaciéres, is another interesting subject of enquiry. The Frenchman's suggestion at Bath, that it might be something akin to the rhomboidal form assumed by dried mud, we believe not to be far from the mark.
But whether the desiccation results from heat or great cold, we cannot determine. We would associate with these other phenomena having, as we believe, a similar- origin-as, for instance, the columnar structure in basalt, which has nothing whatever of a crystalline structure in it. It is curious to observe that basaltic prisms occur in exactly the same relation to the altered substance as do the prisms of ice-that is to say, in beds extending from the one surface to the other, and in cylindrical columns radiating from the centre to the circumference. The same cause produces the columns in wheaten starch. The walls of the vitritied forts in Scotland often exhibit beautiful specimens of the same structure in places where they have been subjected to great heat, though not sufficient to produce vitrificarion. We have also seen very beautiful and remarkably regular pentagonal and hexagonal columns produced in the brick iloor of a baker's oven which had been long in use, and consequently subjected to frequent aud considerable changes of temperature, though never sudicient to produce fusion. And we have often gathered good examples of hexagonal columns from the exposed bituminos shale-beds at Wardie, near Edinburgh.
Review by the Geological magazine (1865), Volume 2, issue 16: