Last summer we were watching the gradual change of the brilliant sunlight on the snows of Mont Blanc as the shadows crept up the pine-covered sides of the valley of Chamonix. We noted how the highest peak—the true summit of Mont Blanc—remained almost white and brilliant when the somewhat lower and nearer Dome de Gouter (so often, when clouds are about, mistaken for the true summit by tourists) had assumed a marvellous shade of saffron-rose colour. The crevasses of the glaciers were marked by an unearthly pale-green tint and delicate purple hues of weird beauty were spreading over the evanescent forms of the great snow-field, when one of the hotel guests—a citizen of Geneva—said, “Ah, yes! Look at them whilst you may, and wonder at them, those glaciers of the Alps. They are but the remnants, the roots, as it were, of the vast glacier which once filled the whole of this vale of Chamonix and spread down into the valley of the Rhone, and ploughed out with the slow movement of its huge mass the deep rock basin of the Lake Leman. Every year they dwindle, as they have dwindled for ages past, and soon—perhaps not more than another 100 years hence—they will have disappeared utterly from human sight and knowledge.” I continued to gaze at the scene, and as the night fell and the distant details were lost to view I felt as though a venerable, but decrepit, friend had passed from my sight, never to return. I was rejoiced to see the glaciers still there when the morning sun showed forth their strange opaque white and faintly green masses on the mountain sides—stupendous outpourings, as it were, of whipped cream tinted with pistachio-nut.

But was it true, that lament of the Genevese savant? Undoubtedly the glaciers in many parts of the Alps have been shrinking for the last thirty years. It is longer than that since I first saw the glaciers of the Chamonix valley, and there is no doubt that they have shrunk up since then, leaving acres of boulders and bare polished rock where was the ice I formerly climbed. The glacier of ArgentiÈre, near the upper end of the valley, is a mile or more shorter than it was; the ice caves which we used to visit at the foot of the Mer de Glace have melted away, and the end of the glacier is now high up above a precipitous surface of polished rock far from the site of the little pavilion, with its gay flag and amiable guardian, who used to exhibit the marvellous ice cavern.

I find on looking into the matter that it is true that there has, during the latter half of the past century, been a great dwindling of the lower end or “snout,” a drawing back, as it were, not only of Swiss glaciers, but of glaciers in other parts of the world—as, for instance, in Alaska and in the Himalayas. But I cannot avoid a feeling of satisfaction in recording the opinion of geological authorities that, contrary to the assertion of the Swiss pessimist, there is not any ground for believing that the present noticeable shrinking is due to a continuous process by which the enormous glaciers of remote ages have been incessantly reduced until now they are but rootlets or stumps of the former masses, destined to evaporate completely under the continued remorseless operation of increasing temperature. On the contrary, it appears that, though there are not accurate records and measurements as to past centuries as there will be as to present and future years, yet there is abundant evidence that Alpine glaciers have grown longer in some centuries and retreated in others. The period of alternate extension and retraction has not been ascertained with accuracy, but by some geologists it is supposed to be about fifty years. The retraction or shrinking is not due to a continuous increase of the temperature of the earth’s atmosphere—or of this hemisphere—but to contending causes which operate alternately towards increase and towards decrease when one or two hundred years are considered. Such are the greater or less rainfall and snowfall over a very large area, and the formation and persistence of clouds, concerned with which are probably those varying quantities—the spots on the sun.

The simple proof that glaciers have extended and again retreated within historic times is furnished by the fact that in some parts of the Alpine range the retreat of a glacier has uncovered ancient miners’ excavations, which must have been worked when the glacier did not reach the spot excavated. Subsequently the glacier advanced, and now after some hundreds of years it has again retreated and exposed the ice-covered borings and workings. The tradition of a glacier-enclosed village in the Zermatt mountains, shut off from the world by the advance of glaciers, lost and mysterious, is evidence that such advance has been observed by the native population.

The natives who live near glaciers know that they advance and retreat, but the fact that the whole glacier is really a slowly flowing viscous mass—a sort of frozen but not immobile river—was only established by scientific observation in the last century. The frozen river is fed by the snow which falls on the higher mountain ridges, and is squeezed into the form of ice instead of snow powder by its own weight as it slips down the inclines, warmed by the unclouded sunshine. The big glaciers move much more rapidly (or perhaps one should say less slowly) in the middle than at the sides. The measurements which have been made differ in different glaciers and in different parts of the same glacier, and show smaller movement in winter than in summer. The advance of the sides is retarded, as in the case of an ordinary river of flowing water, by friction against the rocks, which enclose the glacier as its banks enclose a river. A good average case shows a flow downwards in summer of half a foot a day at the sides and a foot and a half in the middle. The distance below the snow-line to which the flowing glacier descends down a mountain gorge—before it melts away and becomes a river of liquid water—depends, as does the rate at which it moves, in the first place, on the temperature of the region and on the sharpness of the slope. A glacier will flow downwards (as will a lump of pitch) along a scarcely perceptible incline, but more slowly than down a steeper incline, and it will, consequently, get further down into the warm valley without altogether melting away when the slope is steep.

But apart from these considerations, the bigger and thicker (or deeper) the glacier, that is to say, the more snow which each year falls at its starting-place and goes to making it, the further down will it flow before melting away; and it is the heavy snowfall of many years ago or of a series of years long past which has to-day reached in the form of ice the lower end of the glacier. So, though the lower end of the glacier may melt more quickly if the valley has become hotter, yet the heavy snowfalls of fifty years ago may only now have reached the valley, and may quite counterbalance the melting action of the warmer summers. Or reverse conditions, namely, less snow and lower or unchanged temperature in the valley, may prevail.

The Government of India has lately established a definite survey and record of the movement of several Himalayan glaciers and of the variation in the distance to which their “snouts” descend into the valleys. Twelve glaciers were examined last year, and will be properly watched in future. The Yengutsa glacier has gained about two miles in length since Sir Martin Conway visited it in 1892; the great Hispar glacier has slightly retreated. The Hassanabad glacier three years ago increased its length by a rapid progress of the free “snout” of as much as six miles in three months, and is now no longer increasing or advancing! Many years ago it had reached its present position, and then retreated. The rock masses carried on the ice and left in great heaps at the point where the glacier melted away are known as terminal “moraines,” and often serve to show the position to which the snout of a glacier once extended—far below its present limit. A curious fact as to the increase and shrinkage of glaciers is that of two neighbouring glaciers, as in the case of the glacier Blanc and the glacier Noir in DauphinÉ (France), one may be advancing whilst the other is in retreat. Further study and knowledge of the causes of these variations will throw important light on questions of general meteorology.

Although there is no evidence to lead us to suppose that existing glaciers are now actually in a condition of general retreat, leading to their ultimate disappearance, yet it is one of the most certain and interesting results of geological study that some hundred and fifty thousand years ago the northern hemisphere was far colder than it is now, owing partly to the same change in the inclination of the earth’s axis to which I alluded on a former page (p. 81) as affecting the orientation of ancient astronomical temples—a change which diminished, when at its extreme, the effective amount of heat received from the sun in these regions of the earth. The peculiar scratching, polishing, and erosion of rocks, the existence of moraines, and other evidence, prove that enormous glaciers covered the north of Europe, that England and Scotland were in large part covered by a great ice-sheet or glacier, and that the great valleys of Switzerland such as the Rhone Valley and the basin of the Lake of Geneva, were filled by enormous glaciers, which helped to mould and deepen the valleys. The present glaciers are truly the remnants or rootlets of those enormous masses of the glacial epoch. On such of the land surface as was not then covered by ice, existed the hairy elephant or Siberian mammoth, the woolly rhinoceros, wild cattle, lions, bears, hyenas, and other animals now extinct in this part of the world. Man had made his appearance, hunted these animals, and lived in caves. His weapons and carvings and their bones tell us the story in no uncertain terms.

The biggest Swiss glaciers of to-day, compared to the great glacier of the Rhone Valley, of which they are but the highest tributaries, still surviving unmelted among the mountain-tops, are in size as a mountain freshet is to the great stream of Loch Lomond, or as the Serpentine in Hyde Park to the neighbouring Thames. Vast as was the great glacier of the Rhone Valley, and immense as has been the work done by water and ice in carving the great highway in the mountain-mass of Switzerland, it has all been effected since the date of the formation on the sea-bottom and the subsequent elevation of the strata which we call “the chalk”—a deposit which comes not very far down in the series of strata of the earth’s crust. Only 3,000ft. of deposit exist above it, whilst below it are more than 60,000ft. of water-deposited or “sedimentary” rocks. The huge Alps have risen since the date of the “chalk,” for we find strata containing marine shells of the Tertiary period at a height of 10,000ft. in those mountains. Where those shells now are was the bottom of the sea at a comparatively recent date, probably not more than fifty million years ago! And not only have the Alps been raised since then from the sea level to 15,000ft. (the height of Mont Blanc), but the huge mountain valleys and the great chasm of the Rhone Valley many miles wide, with its floor thousands of feet below the mountain ridges, have been scoured out. Deeper and wider it has gradually become as it has taken shape, whilst the mountain sides have been removed first by water and later by ice—by the great glacier consisting of solid ice, miles wide and a thousand and more feet in thickness. The water no longer fills the valley in solid form, but once again rushes along as an irresistible torrent, tearing and wearing the rock without rest or mercy, carrying it off by thousands of tons day by day, year by year, to the plains of Provence and the deep floor of the Mediterranean Sea.

The blue colour of the glacier ice—like that of pure water—is now known to be due to no impurity or admixture of other substances. It does not, as was supposed by Tyndall, owe its blueness to a dust of finest colourless particles as do blue smoke, the blue sky, and as do the blue eyes which have attracted the observation of naturalists (and others) in Ireland and the North of Europe. Water, whether liquid or solid, is blue, just as “blue copperas” is, or as “Prussian blue” is; but light must pass through some ten or twenty feet thickness of it to make the colour evident to our eyes. The green tint is due to an admixture of yellow, the exact cause of which is not quite easy to discover. Probably it is due to minute quantities of earthy matter mixed with the surface snow.

The pressing of the high-lying snow, so as to form solid ice or “glacier,” is concerned with the same property of snow as that which enables us to make snow “bind” into a snowball. You cannot make snowballs during very hard frost—the snow must be in air of a thawing temperature at the moment it is squeezed by the hand. The hand itself will not be warm enough to produce that temperature when the thermometer is below freezing-point. The snow commences to melt in the hand when one squeezes it, and then when the squeezing is stopped the water formed quickly freezes again and cements the snow particles together to form ice, enclosing innumerable minute bubbles. The heat of the sun and the pressure of the weight of the snow itself take the place in the mountains of the warmth and pressure of the human hand. The minute air bubbles make the newest glacier-ice white and opaque, especially when seen in a great mass; but gradually they get squeezed together, and the glacier ice becomes first “fibrous” in appearance, and then, after long years of pressure by its own weight, fairly clear. Ice in great masses has the properties of a viscous body, like pitch or soft sealing-wax, owing to the fact that wherever the solid mass breaks its particles melt a very little and then freeze again. Under increased pressure ice melts at a lower temperature than when it is not subjected to pressure. When the pressure is removed the water freezes again. Thus crushed ice or snow can be put into a “squeeze-mould” and pressed, so as to form a solid mass of ice of any shape you may choose. Four or five slabs of ice, placed one over the other, very soon become, owing to this property, one continuous solid mass. White glacier ice is so full of air bubbles as to be comparable in structure to sponge, or, more closely, to cork. A cube of such ice exposes, owing to its rough air-hole pitted surface, a much larger surface of contact to the atmosphere than does a cube of perfectly smooth clear ice. Consequently in a warm room or chamber the white ice melts much more quickly than does the clear, and hence you should choose clear ice rather than white ice if you wish for a block which will last.

Before leaving the glaciers, let me briefly relate an incident arising from their slow but regular downward flow to the region where they melt away and deposit, as a terminal moraine, the burden of rocks they have received years before in regions far above. A young man of five-and-twenty, on his honeymoon, visited the Alps, and ventured alone on to a glacier. He fell into a deep “crevasse,” or ice-fissure, and his body was not recovered. The exact spot where he fell into the ice-chasm was recognised, and the mountain-folk, who knew their glacier and its rate of movement well, told the broken-hearted young widow that it would take thirty years before that region of the glacier would have moved so far downwards as to reach the lowest limit, and in due course melt away. She haunted the glacier in which her young husband was entombed year after year, and at last, when she was now grey-headed and withered by time, that special tract of ice had descended so far, and was so near the thawing, thinned-out margin of the glacier that they were able to break into it with axe and pole. Then she, an old woman, had a wonderful experience. They led her to the glacier’s edge. Her young husband, preserved these thirty years in the ice, which had melted around him and re-frozen, lay there unchanged. His features were not marred by the lapse of years, nor was his clothing rent or injured. He seemed as one asleep, resting after a long day’s climb, and she, poor soul, had, during a blissful interval, the conviction that all those weary years of waiting were but a long, bad dream, that she, too, still was young, and was waking, as she had loved to do long years ago, in time to see him lift his lids and smile.