THE great subalpine lakes surround the Alps like a necklace of jewels. They literally depend upon and from the mountains, and the threads by which they are attached are silver torrents and glittering streams coursing down from on high. The jewels in this necklace are made iridescent by the play and interplay of sun and season. They respond to the action of distant snow masses and glaciers on the march.
Of the Italian lakes in particular it may be said that they are great reflectors of the Alps, lying meekly at the feet of the giants and mirroring outline and colour upon their polished faces.
From the valleys on the Italian side the Alps are seen to rise to their full stature, for the southern slope is much steeper than the northern one. Hence the views from the Italian lakes region permit a special breadth and height and enable one to study mountain formations with a certain degree of comprehension. In order to obtain some idea of prevalent theories in regard to the origin of the Alps, and hence of the great water pockets or lake reservoirs at their feet, take your stand upon one of those lesser, but commanding, heights in the Italian lakes region, whence Alps and plain can be swept by the eye, Monte Motterone, Sasso del Ferro, Monte Generoso, or any other of the summits favourably placed for a bird’s-eye view. Then start your theory by imagining yourself back in the Permian, Liassic, Jurassic, or Cretaceous period, when the deep sea is believed to have lain upon the surface of the earth where the Alps now rise, and the very height to which you have climbed was not.
Let us now suppose these ages to have disappeared into the dim perspective of the past, and the quiet which brooded upon the face of the waters to have been broken by a total transformation. The earth, in cooling, has contracted, the crust has been crumpled into folds and the raw material of the Alps, the strata out of which the peaks are to be carved, stand up above the sea, upheaved, not by pressure from below, but from the sides. As soon as these vast arching folds have risen from the bottom of the sea into the clouds, the process of disintegration and denudation begins under the influence of heat and cold, wind and water, snow and rain. Rivers form, and wear and tear great chasms, gorges, and valleys down the flanks of the folds on their way to the sea. Presently the once solid mass is no longer intact, but is cut into ridges and ranges, sections and groups. The Alps stand forth as lofty peaks; the rivers deposit their débris and detritus, the refuse of the heights, in all directions, and fill up Central Europe with sand and gravel. The Ice Age follows, and when that period of cold is finally broken, the Alps appear somewhat as we see them today, and perhaps some of the lakes, too.
But the peaks point skyward and must take the consequences. The disintegrating elemental forces that make for a dead level will not leave them alone. The destructive agencies cut and slash, peck and pinch the giants, nipping off a bit here, tearing down a corner there. No sooner has a creditable outline, a rounded form, or a noble horn been established, than these destructive agencies, like tireless imps, are found at work there with their little hammers, pincers, augers, gimlets, and saws, chipping and disfiguring the fair mountain faces. They try to alter even the mountain meadows, familiar to many generations of men in the valleys below, and seek to tamper with the kindly mountain slopes that have fed the grazing cattle and supported the forests from which to build many thousand cottages and kindle countless fires upon family hearthstones. Still there are compensations and readjustments. The denudation of the Alps fertilizes the plain, filling it with alluvial deposits. In the case of the plain of Lombardy borings indicate that the alluvium is of tremendous, but as yet unknown, depth.
But what of the alpine and subalpine lakes? What say modern theories as to their origin? Much study has been devoted to this question of lake formation by conscientious natural scientists, among others by Englishmen such as Tyndall, Ramsay, Ball, and Lubbock, by the Italians Gastaldi and De Mortillet, and by the Swiss Desor, Studer, and Favre. According to these investigators, there would seem to be room for considerable difference of opinion in regard to the origin of the great lakes which surround the Alps and catch their snow and rain fall, north and south. The lakes doubt-less arose after the worst of the Ice Age was past and coincidentally with the retreat of the glaciers from the plains, back nearer to their mountain fastnesses and snow sources.
Some of the smaller alpine lakes have been produced by moraines, or rockfalls, blocking the progress of torrents or rivers down to the valleys and causing the water to back up and rise, until it once more made an outlet for itself. Lakes Orta and Iseo arose in this manner.
As for the larger alpine lakes, it was at one time quite generally held in geological circles that their basins had been scooped out wholly by the action of glaciers, rein-forced by rivers. But the great depth of most of the Italian subalpine lakes seems to make this theory unsatisfactory. The bottoms of some of these lakes descend below the level of the sea, those of Maggiore and Como more than twelve hundred feet below sea-level. It would be difficult to imagine such profound excavations made by ice or water, so far below the normal water level.
Another explanation has therefore been gaining ground more recently, which is based on the supposition that there has been a subsidence of the Central Alps since the Ice Age. This subsidence would tend to raise the surrounding country, at least relatively, and the rivers which flowed downward from the Alps would find the lower ends of their valleys seemingly tilted up, as it were, and their waters would be caught in veritable pockets or reservoirs. Thus the lakes, as we see them to-day, would be the result, first of ice and water carving out valleys, and then of subsidence altering the level of the valley floors. There is still, however, the possibility that the larger Italian subalpine lakes are the remnants of a sea which once undoubtedly covered the whole plain of Lombardy.
The natural tendency has been for the same process which denudes the Alps also to diminish the area of the Italian lakes. Material has been deposited upon the lake bottoms by the rivers that drain them. Especially is this filling-in process noticeable at the upper ends of the lakes. Thus Lago Maggiore doubtless once extended as far north as Bellinzona and Lake Como to Chiavenna.
The colour of alpine and subalpine lakes has long been a source of special joy and wonder to tourists and travellers, artists and poets. There is considerable variety and wide alternation between the extremes of ultramarine blue and deep green. Every intermediate shade is to be found somewhere, in some alpine or subalpine lake, or in some portion of such a lake. Among the Italian lakes a rich blue, similar to that of the Mediterranean, predominates, but there is also a great diversity in colour which serves to emphasize the special characteristics of each lake. Above all, the changing conditions of atmosphere, seasons, wind, and rain, and especially of sun, cause a constant play and interplay which largely modify the original, or basic colour and act as secondary influences. It has been popularly supposed that the blueness of water in general is due to the reflection of the blue sky, but actual experiments indicate that pure water is naturally blue, and so it would follow that the clearest lakes are also the bluest. The green of certain lakes may be due to minute quantities of vegetable matter in solution, to the shallowness of water lying over yellowish sand or rock, to the action of storms in stirring up sediment, or even to microscopic algæ.
Whatever the supposed causes of their changing colours, the Italian lakes them-selves remain ever attractive in a sort of unexpectedly spontaneous way. When we think their beauties have been sufficiently differentiated, arranged, sorted, and classified, and their relative values compared, then a day of unusual conditions makes itself felt and all calculations fail. Criticism can-not thrive in their atmosphere nor uncharitableness face their kindly loveliness. They are all friends of men and vary only in their special virtues, they have no faults.