by Grant Allen
It may sound at first hearing a strange thing to say so, but the whole of that vast gulf, from Turin to Venice, has been entirely filled up within the human period by the mud sheet brought down by mountain torrents from the Alps and the Apennines.
A parallel elsewhere will make this easier of belief. You have looked down, no doubt, from the garden of the hotel at Glion upon the lake of Geneva and the valley of the Rhone about Villeneuve and Aigle. If so, you can understand from personal knowledge the first great stage in the mud-filling process; for you must have observed for yourself from that commanding height that the lake once extended a great deal farther up country towards Bex and St. Maurice than it does at present. You can still trace at once on either side the old mountainous banks, descending into the plain as abruptly and unmistakably as they still descend to the water’s edge at Montreux and Vevey. But the silt of the Rhone, brought down in great sheets of glacier mud (about which more anon) from the Furca and the Jungfrau and the Monte Rosa chain, has completely filled in the upper nine miles of the old lake basin with a level mass of fertile alluvium. There is no doubt about the fact: you can see it for yourself with half an eye from that specular mount (to give the Devil his due, I quote Milton’s Satan): the mud lies even from bank to bank, raised only a few inches above the level of the lake, and as lacustrine in effect as the veriest geologist on earth could wish it. Indeed, the process of filling up still continues unabated at the present day where the mud-laden Rhone enters the lake at Bouveret, to leave it again, clear and blue and beautiful, under the bridge at Geneva. The little delta which the river forms at its mouth shows the fresh mud in sheets gathering thick upon the bottom. Every day this new mud-bank pushes out farther and farther into the water, so that in process of time the whole basin will be filled in, and a level plain, like that which now spreads from Bex and Aigle to Villeneuve, will occupy the entire bed from Montreux to Geneva.
Turn mentally to the upper feeders of the Po itself, and you find the same causes equally in action. You have stopped at Pallanza — Garoni’s is so comfortable. Well, then, you know how every Alpine stream, as it flows, full-gorged, into the Italian lakes, is busily engaged in filling them up as fast as ever it can with turbid mud from the uplands. The basins of Maggiore, Como, Lugano, and Garda are by origin deep hollows scooped out long since during the Great Ice Age by the pressure of huge glaciers that then spread far down into what is now the poplar-clad plain of Lombardy. But ever since the ice cleared away, and the torrents began to rush headlong down the deep gorges of the Val Leventina and the Val Maggia, the mud has been hard at work, doing its level best to fill those great ice-worn bowls up again. Near the mouth of each main stream it has already succeeded in spreading a fan-shaped delta. I will not insult you by asking you at the present time of day whether you have been over the St. Gothard. In this age of trains de luxe I know to my cost everybody has been everywhere. No chance of pretending to superior knowledge about Japan or Honolulu; the tourist knows them. Very well, then; you must remember as you go past Bellinzona — revolutionary little Bellinzona with its three castled crags — you look down upon a vast mud flat by the mouth of the Ticino. Part of this mud flat is already solid land, but part is mere marsh or shifting quicksand. That is the first stage in the abolition of the lakes: the mud is annihilating them.
Maggiore, indeed, least fortunate of the three main sheets, is being attacked by the insidious foe at three points simultaneously. At the upper end, the Ticino, that furious radical river, has filled in a large arm, which once spread far away up the valley towards Bellinzona. A little lower down, the Maggia near Locarno carries in a fresh contribution of mud, which forms another fan-shaped delta, and stretches its ugly mass half across the lake, compelling the steamers to make a considerable detour eastward. This delta is rapidly extending into the open water, and will in time fill in the whole remaining space from bank to bank, cutting off the upper end of the lake about Locarno from the main basin by a partition of lowland. This upper end will then form a separate minor lake, and the Ticino will flow out of it across the intervening mud flat into the new and smaller Maggiore of our great-great-grandchildren. If you doubt it, look what the torrent of the Toce, the third assailing battalion of the persistent mud force, has already done in the neighbourhood of Pallanza. It has entirely cut off the upper end of the bay, that turns westward towards the Simplon, by a partition of mud; and this isolated upper bit forms now in our own day a separate lake, the Lago di Mergozzo, divided from the main sheet by an uninteresting mud bank. In process of time, no doubt, the whole of Maggiore will be similarly filled in by the advancing mud sheet, and will become a level alluvial plain, surrounded by mountains, and greatly admired by the astute Piedmontese cultivator.
What is going on in Maggiore is going on equally in all the other sub-Alpine lakes of the Po valley. They are being gradually filled in, every one of them, by the aggressive mud sheet. The upper end of Lugano, for example, has already been cut off, as the Lago del Piano, from the main body; and the piano itself, from which the little isolated tarn takes its name, is the alluvial mud fiat of a lateral torrent — the mud flat, in fact, which the railway from Porlezza traverses for twenty minutes before it begins its steep and picturesque climb by successive zigzags over the mountains to Menaggio. Similarly the influx of the Adda at the upper end of Como has cut off the Lago di Mezzola from the main lake, and has formed the alluvial level that stretches so drearily all around Colico. Slowly the mud fiend encroaches everywhere on the lakes; and if you look for him when you go, there you can see him actually at work every spring under your very eyes, piling up fresh banks and deltas with alarming industry, and preparing (in a few hundred thousand years) to ruin the tourist trade of Cadenabbia and Bellagio.
If we turn from the lakes themselves to the Lombard plain at large, which is an immensely older and larger basin, we see traces of the same action on a vastly greater scale. A glance at the map will show the intelligent and ever courteous reader that the ‘wandering Po’ — I drop into poetry after Goldsmith — flows much nearer the foot of the Apennines than of the Alps in the course of its divagations, and seems purposely to bend away from the greater range of mountains. Why is this, since everything in nature must needs have a reason? Well, it is because, when the mud first began to accumulate in the old Lombard bay of the Adriatic, there was no Po at all, whether wandering or otherwise: the big river has slowly grown up in time by the union of the lateral torrents that pour down from either side, as the growth of the mud flat brought them gradually together. Careful study of a good map will show how this has happened, especially if it has the plains and mountains distinctively tinted after the excellent German fashion. The Ticino, the Adda, the Mincio, if you look at them close, reveal themselves as tributaries of the Po, which once flowed separately into the Lombard bay; the Adige, the Piave, the Tagliamento farther along the coast, reveal themselves equally as tributaries of the future Po, when once the great river shall have filled up with its mud the space between Trieste and Venice, though for the moment they empty themselves and their store of detritus into the open Adriatic.
Fix your eyes for a moment on Venetia proper, and you will see how this has all happened and is still happening. Each mountain torrent that leaps from the Tyrolese Alps bring down in its lap a rich mass of mud, which has gradually spread over a strip of sea some forty or fifty miles wide, from the base of the mountains to the modern coast-line of the province. Near the sea — or, in other words, at the temporary outlet — it forms banks and lagoons, of which those about Venice are the best known to tourists, though the least characteristic. For miles and miles between Venice and Trieste the shifting north shore of the Adriatic consists of nothing but such accumulating mud banks. Year after year they push farther seaward, and year after year fresh islets and shoals grow out into the waves beyond the temporary deltas. In time, therefore, the gathering mud banks of these Alpine torrents must join the greater mud bank that runs rapidly seaward at the delta of the
Po. As soon as they do so the rivers must rush together, and what was once an independent stream, emptying itself into the Adriatic, must become a tributary of the Po, helping to swell the waters of that great united river. The Adige has now just reached this state: its delta is continuous with the delta of the Po, and their branches interosculate. The Mincio and the Adda reached it ages since: the Piave and the Livenia will not reach it for ages. In Roman days Hatria was still on the sea: it is now some fifteen miles inland.
From all this you can gather why the existing Po flows far from the Alps and nearer the base of the Apennines. The Alpine streams in far distant days brought down relatively large floods of glacial mud; formed relatively large deltas in the old Lombard bay; filled up with relative rapidity their larger half of the basin. The Apennines, less lofty, and free from glaciers, sent down shorter and smaller torrents, laden with far less mud, and capable therefore of doing but little alluvial work for the filling in of the future Lombardy. So the river was pushed southward by the Alpine deposits of the northern streams, leaving the great plains of Cisalpine Gaul spread away to the north of it.
And this land-making action is ceaseless and continuous. About Venice, Chioggia, Maestra, Comacchio, the delta of the Po is still spreading seaward. In the course of ages — if nothing unforeseen occurs meanwhile to prevent it — the Alpine mud will have filled in the entire Adriatic; and the Ionian Isles will spring like isolated mountain ridges from the Adriatic plain, as the Euganean hills — those ‘mountains Euganean’ where Shelley ‘stood listening to the pæan with which the legioned rocks did hail the sun’s uprise majestical’ — spring in our own time from the dead level of Lombardy. Once they in turn were the Euganean islands, and even now to the trained eye of the historical observer they stand up island-like from the vast green plain that spreads flat around them.
Perhaps it seems to you a rather large order to be asked to believe that Lombardy and Venetia are nothing more than an outspread sheet of deep Alpine mud. Well, there is nothing so good for incredulity, don’t you know, as capping the climax. If a man will not swallow an inch of fact, the best remedy is to make him gulp down an ell of it. And, indeed, the Lombard plain is but an insignificant mud flat compared with the vast alluvial plains of Asiatic and American rivers. The alluvium of the Euphrates, of the Mississippi, of the Hoang Ho, of the Amazons would take in many Lombardies and half-a-dozen Venetias without noticing the addition. But I will insist upon only one example — the rivers of India, which have formed the gigantic deep mud flat of the Ganges and the Jumna, one of the very biggest on earth, and that because the Himalayas are the highest and newest mountain chain exposed to denudation. For, as we saw foreshadowed in the case of the Alps and Apennines, the bigger the mountains on which we can draw the greater the resulting mass of alluvium. The Rocky Mountains give rise to the Missouri (which is the real Mississippi); the Andes give rise to Amazons and the La Plata; the Himalayas give rise to the Ganges and the Indus. Great mountain, great river, great resulting mud sheet.
At a very remote period, so long ago that we cannot reduce it to any common measure with our modern chronology, the southern table-land of India — the Deccan, as we call it — formed a great island like Australia, separated from the continent of Asia by a broad arm of the sea which occupied what is now the great plain of Bengal, the North-West, and the Punjaub. This ancient sea washed the foot of the Himalayas, and spread south thence for 600 miles to the base of the Vindhyas. But the Himalayas are high and clad with gigantic glaciers. Much ice grinds much mud on those snow-capped summits. The rivers that flowed from the Roof of the World carried down vast sheets of alluvium, which formed fans at their mouths, like the cones still deposited on a far smaller scale in the Lake of Geneva by little lateral torrents. Gradually the silt thus brought down accumulated on either side, till the rivers ran together into two great systems — one westward — the Indus, with its four great tributaries, Jhelum, Chenab, Ravee, Sutlej; one eastward, the Ganges, reinforced lower down by the sister streams of the Jumna and the Brahmapootra. The colossal accumulation of silt thus produced filled up at last all the great arm of the sea between the two mountain chains, and joined the Deccan by slow degrees to the continent of Asia. It is still engaged in filling up the Bay of Bengal on one side by the detritus of the Ganges, and the Arabian Sea on the other by the sand-banks of the Indus.
In the same way, no doubt, the silt of the Thames, the Humber, the Rhine, and the Meuse tend slowly (bar accidents) to fill up the North Sea, and anticipate Sir Edward Watkin by throwing a land bridge across the English Channel. If ever that should happen, then history will have repeated itself, for it is just so that the Deccan was joined to the mainland of Asia.
One question more. Whence comes the mud? The answer is, Mainly from the detritus of the mountains. There it has two origins. Part of it is glacial, part of it is leaf-mould. In order to feel we have really got to the very bottom of the mud problem — and we are nothing if not thorough — we must examine in brief these two separate origins.
The glacier mud is of a very simple nature. It is disintegrated rock, worn small by the enormous millstone of ice that rolls slowly over the bed, and deposited in part as ‘terminal moraine’ near the summer melting-point. It is the quantity of mud thus produced, and borne down by mountain torrents, that makes the alluvial plains collect so quickly at their base. The mud flats of the world are in large part the wear and tear of the eternal hills under the planing action of the eternal glaciers.
But let us be just to our friends. A large part is also due to the industrious earth-worm, whose place in nature Darwin first taught us to estimate at its proper worth. For there is much detritus and much first-rate soil even on hills not covered by glaciers. Some of this takes its origin, it is true, from disintegration by wind or rain, but much more is caused by the earth-worm in person. That friend of humanity, so little recognized in his true light, has a habit of drawing down leaves into his subterranean nest, and there eating them up, so as to convert their remains into vegetable mould in the form of worm-casts. This mould, the most precious of soils, gets dissolved again by the rain, and carried off in solution by the streams to the sea or the lowlands, where it helps to form the future cultivable area. At the same time the earthworms secrete an acid, which acts upon the bare surface of rock beneath, and helps to disintegrate it in preparation for plant life in unfavourable places. It is probable that we owe almost more on the whole to these unknown but conscientious and industrious annelids than even to those ‘mills of God’ the glaciers, of which the American poet justly observes that though they grind slowly, yet they grind exceedingly small.
In the last resort, then, it is mainly on mud that the life of humanity in all countries bases itself. Every great plain is the alluvial deposit of a great river, ultimately derived from a great mountain chain. The substance consists as a rule of the débris of torrents, which is often infertile, owing to its stoniness and its purely mineral character; but wherever it has lain long enough to be covered by earth-worms with a deep black layer of vegetable mould, there the resulting soil shows the surprising fruitfulness one gets (for example) in Lombardy, where twelve crops a year are sometimes taken from the meadows. Everywhere and always the amount and depth of the mud is the measure of possible fertility; and even where, as in the Great American Desert, want of water converts alluvial plains into arid stretches of sand-waste, the wilderness can be made to blossom like the rose in a very few years by artificial irrigation. The diversion of the Arkansas River has spread plenty over a vast sage scrub; the finest crops in the world are now raised over a tract of country which was once the terror of the traveller across the wild west of America.
THE GREENWOOD TREE.
It is a common, not to say a vulgar error, to believe that trees and plants grow out of the ground. And of course, having thus begun by calling it bad names, I will not for a moment insult the intelligence of my readers by supposing them to share so foolish a delusion. I beg to state from
the outset that I write this article entirely for the benefit of Other People. You and I, O proverbially Candid and Intelligent One, it need hardly be said, are better informed. But Other People fall into such ridiculous blunders that it is just as well to put them on their guard beforehand against the insidious advance of false opinions. I have known otherwise good and estimable men, indeed, who for lack of sound early teaching on this point went to their graves with a confirmed belief in the terrestrial origin of all earthly vegetation. They were probably victims of what the Church in its succinct way describes and denounces as Invincible Ignorance.
Now, the reason why these deluded creatures supposed trees to grow out of the ground, instead of out of the air, is probably only because they saw their roots there.
Of course, when people see a wallflower rooted in the clefts of some old church tower, they don’t jump at once to the inane conclusion that it is made of rock — that it derives its nourishment direct from the solid limestone; nor when they observe a barnacle hanging by its sucker to a ship’s hull, do they imagine it to draw up its food incontinently from the copper bottom. But when they see that familiar pride of our country, a British oak, with its great underground buttresses spreading abroad through the soil in every direction, they infer at once that the buttresses are there, not — as is really the case — to support it and uphold it, but to drink in nutriment from the earth beneath, which is just about as capable of producing oak-wood as the copper plate on the ship’s hull is capable of producing the flesh of a barnacle. Sundry familiar facts about manuring and watering, to which I will return later on, give a certain colour of reasonableness, it is true, to this mistaken inference. But how mistaken it really is for all that, a single and very familiar little experiment will easily show one.
