The Earth As Modified By Human Action Part 15

"The elements of destruction are increasing in violence. The devastation advances in geometrical progression as the higher slopes are bared of their wood, and 'the ruin from above,' to use the words of a peasant, 'helps to hasten the desolation below.'

"The Alps of Provence present a terrible aspect. In the more equable climate of Northern France, one can form no conception of those parched mountain gorges where not even a bush can be found to shelter a bird, where, at most, the wanderer sees in summer here and there a withered lavender, where all the springs are dried up, and where a dead silence, hardly broken by even the hum of an insect, prevails. But if a storm bursts forth, ma.s.ses of water suddenly shoot from the mountain heights into the shattered gulfs, waste without irrigating, deluge without refres.h.i.+ng the soil they overflow in their swift descent, and leave it even more seared than it was from want of moisture. Man at last retires from the fearful desert, and I have, the present season, found not a living soul in districts where I remember to have enjoyed hospitality thirty years ago."

In 1853, ten years after the date of Blanqui's memoir, M. de Bonville, prefect of the Lower Alps, addressed to the Government a report in which the following pa.s.sages occur:

"It is certain that the productive mould of the Alps, swept off by the increasing violence of that curse of the mountains, the torrents, is daily diminis.h.i.+ng with fearful rapidity. All our Alps are wholly, or in large proportion, bared of wood. Their soil, scorched by the sun of Provence, cut up by the hoofs of the sheep, which, not finding on the surface the gra.s.s they require for their sustenance, gnaw and scratch the ground in search of roots to satisfy their hunger, is periodically washed and carried off by melting snows and summer storms.

"I will not dwell on the effects of the torrents. For sixty years they have been too often depicted to require to be further discussed, but it is important to show that their ravages are daily extending the range of devastation. The bed of the Durance, which now in some places exceeds a mile and a quarter in width, and, at ordinary times, has a current of water less than eleven yards wide, shows something of the extent of the damage." [Footnote: In the days of the Roman Empire the Durance was a navigable, or at least a boatable, river, with a commerce so important that the boatmen upon it formed a distinct corporation.--Ladoucette, Histoire, etc., des Hautes Alpes, p. 354.

Even as early as 1789 the Durance was computed to have already covered with gravel and pebbles not less than 130,000 acres, "which, but for its inundations, would have been the finest land in the province."--Arthur Young, Travels in France, vol i., ch. i.] Where, ten years ago, there were still woods and cultivated grounds to be seen, there is now but a vast torrent; there is not one of our mountains which has not at least one torrent, and new ones are daily forming.

"An indirect proof of the diminution of the soil is to be found in the depopulation of the country. In 1852 I reported to the General Council that, according to the census of that year, the population of the department of the Lower Alps had fallen off no less than 5,000 souls in the five years between 1846 and 1851.

"Unless prompt and energetic measures are taken, it is easy to fix the epoch when the French Alps will be but a desert. The interval between 1851 and 1856 will show a further decrease of population. In 1862 the ministry will announce a continued and progressive reduction, in the number of acres devoted to agriculture; every year will aggravate the evil and in half a century France will count more ruins, and a department the less."

Time has verified the predictions of De Bonville. The later census returns show a progressive diminution in the population of the departments of the Lower Alps, the Isere, Drome, Ariege, the Upper and the Lower Pyrenees, Lozere, the Ardennes, Doubs, the Vosges, and, in short, in all the provinces formerly remarkable for their forests. This diminution is not to be ascribed to a pa.s.sion for foreign emigration, as in Ireland, and in parts of Germany and of Italy; it is simply a transfer of population from one part of the empire to another, from soils which human folly has rendered uninhabitable, by ruthlessly depriving them of their natural advantages and securities, to provinces where the face of the earth was so formed by nature as to need no such safeguards, and where, consequently, she preserves her outlines in spite of the wasteful improvidence of man. [Footnote: Between 1851 and 1856 the population of Languedoc and Provence had increased by 101,000 souls.

The augmentation, however, was wholly in the provinces of the plains, where all the princ.i.p.al cities are found. In these provinces the increase was 204,000, while in the mountain provinces there was a diminution of 103,000. The reduction of the area of arable land is perhaps even more striking. In 1842 the department of the Lower Alps possessed 90,000 hectares, or nearly 245,000 acres, of cultivated soil.

In 1852 it had but 74,000 hectares. In other words, in ten years 25,000 hectares, or 61,000 acres, had been washed away, or rendered worthless for cultivation, by torrents and the abuses of pasturage.--Clave, Etudes, pp. 66, 67.]

Floods of the Ardeche.

The River Ardeche, in the French department of that name, has a perennial current in a considerable part of its course, and therefore is not, technically speaking, a torrent; but the peculiar character and violence of its floods is due to the action of the torrents which discharge themselves into it in its upper valley, and to the rapidity of the flow of the water of precipitation from the surface of a basin now almost bared of its once luxuriant woods. [Footnote: The original forests in which the basin of the Ardeche was rich have been rapidly disappearing for many years, and the terrific violence of the inundations which are now laying it waste is ascribed, by the ablest investigators, to that cause. In an article inserted in the Annales Forestieres for 1843, quoted by Hohenstein, Der Wald, p. 177, it is said that about one-third of the area of the department had already become absolutely barren, in consequence of clearing, and that the destruction of the woods was still going on with great rapidity. New torrents were constantly forming, and they were estimated to have covered more than 70,000 acres of good land, or one-eighth of the surface of the department, with sand and gravel.] A notice of these floods may therefore not inappropriately be introduced in this place.

The floods of the Ardeche and other mountain streams are attended with greater immediate danger to life and property than those of rivers of less rapid flow, because their currents are more impetuous, and they rise more suddenly and with less previous warning. At the same time, their ravages are confined within narrower limits, the waters retire sooner to their accustomed channel, and the danger is more quickly over, than in the case of inundations of larger rivers. The Ardeche drains a basin of 600,238 acres, or a little less than nine hundred and thirty-eight square miles. Its remotest source is about seventy-five miles, in a straight line, from its junction with the Rhone, and springs at an elevation of four thousand feet above that point. At the lowest stage of the river, the bed of the Cha.s.sezac, its largest and longest tributary, is in many places completely dry on the surface--the water being sufficient only to supply the subterranean channels of infiltration--and the Ardeche itself is almost everywhere fordable, even below the mouth of the Cha.s.sezac. But in floods, the river has sometimes risen more than sixty feet at the Pont d'Arc, a natural arch of two hundred feet chord, which spans the stream below its junction with all its important affluents. At the height of the inundation of 1857, the quant.i.ty of water pa.s.sing this point--after deducting thirty per cent.

for material transported with the current and for irregularity of flow--was estimated at 8,845 cubic yards to the second, and between twelve o'clock at noon on the 10th of September of that year and ten o'clock the next morning, the water discharged through the pa.s.sage in question amounted to more than 450,000,000 cubic yards. This quant.i.ty, distributed equally through the basin of the river, would cover its entire area to a depth of more than five inches.

The Ardeche rises so suddenly that, in the inundation of 1846, the women who were was.h.i.+ng in the bed of the river had not time to save their linen, and barely escaped with their lives, though they instantly fled upon hearing the roar of the approaching flood. Its waters and those of its affluents fall almost as rapidly, for in less than twenty-four hours after the rain has ceased in the Cevennes, where it rises, the Ardeche returns within its ordinary channel, even at its junction with the Rhone. In the flood of 1772, the water at La Beaume de Ruoms, on the Beaume, a tributary of the Ardeche, rose thirty-five feet above low water but the stream was again fordable on the evening of the same day.

The inundation of 1827 was, in this respect, exceptional, for it continued three days, during which period the Ardeche poured into the Rhone 1,305,000,000 cubic yards of water.

The Nile delivers into the sea 101,000 cubic feet or 3,741 cubic yards per second, on an average of the whole year. [Footnote: Sir John F.

Herschel, citing Talabot as his authority, Physical Geography (24).

In an elaborate paper on "Irrigation," printed in the United States Patent Report for 1860, p. 169, it is stated that the volume of water poured into the Mediterranean by the Nile in twenty-four hours, at low water, is 150,566,392,368 cubic meters; at high water, 705,514,667,440 cubic metres. Taking the mean of these two numbers, the average daily delivery of the Nile would be 428,081,059,808 cubic metres, or more than 550,000,000,000 cubic yards. There is some enormous mistake, probably a typographical error, in this statement, which makes the delivery of the Nile seventeen hundred times as great as computed by Talabot, and more than physical geographers have estimated the quant.i.ty supplied by all the rivers on the face of the globe.] This is equal to 323,222,400 cubic yards per day. In a single day of flood, then, the Ardeche, a river too insignificant to be known except in the local topography of France, contributed to the Rhone once and a half, and for three consecutive days once and one third, as much as the average delivery of the Nile during the same periods, though the basin of the latter river probably contains 1,000,000 square miles of surface, or more than one thousand times as much as that of the former.

The average annual precipitation in the basin of the Ardeche is not greater t.i.tan in many other parts of Europe, but excessive quant.i.ties of rain frequently fall in that valley in the autumn. On the 9th. of October, 1827, there fell at Joyeuse, on the Beaume, no less than thirty-one inches between three o'clock in the morning and midnight.

Such facts as this explain the extraordinary suddenness and violence of the floods of the Ardeche, and the basins of many other tributaries of the Rhone exhibit meteorological phenomena not less remarkable.

[Footnote: The Drac, a torrent emptying into the Isere a little below Gren.o.ble, has discharged 5,200, the Isere, which receives it, 7,800 cubic yards, and the Durance, above its junction with the Isere, an equal quant.i.ty, per second.--Montluisant, Note sur les Dessechements, etc., Annales des Ponts et Chaussees, 1833, 2me semestre p. 288.

The Upper Rhone, which drains a basin of about 1,900 square miles, including seventy-one glaciers, receives many torrential affluents, and rain-storms and thaws are sometimes extensive enough to affect the whole tributary system of its narrow valley. In such cases its current swells to a great volume, but previously to the floods of the autumn of 1868 it was never known to reach a discharge of 2,600 cubic yards to the second.

On the 28th of September in that year, however, its delivery amounted to 3,700 cubic yards to the second, which is about equal to the mean discharge of the Nile.--Berichte der Experten-Commission uber die Ueberschaeemmungen im Jahr 1868, pp. 174,175.

The floods of some other French rivers, which have a more or less torrential character, scarcely fall behind those of the Rhone. The Loire, above Roanne, has a basin of 2,471 square miles, or about twice and a half the area of that of the Ardeche. In some of its inundations it has delivered above 9,500 cubic yards per second, or 400 times its low-water discharge.--Belgrand, De l'Influence des Forets, etc., Annales des Ponts et Chaussees, 1854, 1er semestre, p.15, note.

The ordinary low-water discharge of the Seine at Paris is nearly 100 cubic yards per second. Belgrand gives a list of eight floods of that river within the last two centuries, in which it has delivered thirty times that quant.i.ty.]

The Rhone, therefore, is naturally subject to great and sudden inundations, and the same remark may be applied to most of the princ.i.p.al rivers of France, because the geographical character of all of them is approximately the same.

The volume of water in the floods of most great rivers is determined by the degree in which the inundations of the different tributaries are coincident in time. Were all the affluents of the Lower Rhone to pour their highest annual floods into its channel at once--as the smaller tributaries of the Upper Rhone sometimes do--were a dozen Niles to empty themselves into its bed at the same moment, its water would rise to a height and rush with an impetus that would sweep into the Mediterranean the entire population of its banks, and all the works that man has erected upon the plains which border it. But such a coincidence can never happen. The tributaries of this river run in very different directions, and some of them are swollen princ.i.p.ally by the melting of the snows about their sources, others almost exclusively by heavy rains.

When a damp southeast wind blows up the valley of the Ardeche, its moisture is condensed, and precipitated in a deluge upon the mountains which embosom the headwaters of that stream, thus producing a flood, while a neighboring basin, the axis of which lies transversely or obliquely to that of the Ardeche, is not at all affected. [Footnote: "There is no example of a coincidence between great floods of the

Ardeche and of the Rhone, all the known inundations of the former having taken place when the latter was very low."--MARDIGNY, Memoire sur les Inondations des Rivieres de l'Ardeche, p. 26.

The same observation may be applied to the tributaries of the Po, their floods being generally successive, not contemporaneous. The swelling of the affluents of the Amazon, and indeed of most large rivers, is regulated by a similar law. See Messedaglia, a.n.a.lisi dell' opera di Champion, etc., p. 103.

The floods of the affluents of the Tiber form an exception to this law, being generally coincident, and this is one of the explanations of the frequency of destructive inundations in that river.--Lombardini, Guida allo Studio dell' Idrologia, ff. 68; same author, Esame degli studi sul Tevere.

I take this occasion to acknowledge myself indebted to Mardigny's interesting memoir just quoted for all the statements I make respecting the floods of the Ardeche, except the comparison of the volume of its water with that of the Nile.] It is easy to see that the damage occasioned by such floods as I have described must be almost incalculable, and it is by no means confined to the effects produced by overflow and the mechanical force of the superficial currents. In treating of the devastations of torrents, I have hitherto confined myself princ.i.p.ally to the erosion of surface and the transportation of mineral matter to lower grounds by them. The general action of torrents, as thus fur shown, tends to the ultimate elevation of their beds by the deposit of the earth, gravel, and stone conveyed by them; but until they have thus raised their outlets so as sensibly to diminish the inclination of their channels--and sometimes when extraordinary floods give the torrents momentum enough to sweep away the acc.u.mulations which they have themselves heaped up--the swift flow of their currents, aided by the abrasion of the rolling rocks and gravel, scoops their beds constantly deeper, and they consequently not only undermine their banks, but frequently sap the most solid foundations which the art of man can build for the support of bridges and hydraulic structures. [Footnote: In some cases where the bed of rapid Alpine streams is composed of very hard rock--as is the case in many of the valleys once filled by ancient glaciers--and especially where they are fed by glaciers not overhung by crumbling cliffs, the channel may remain almost unchanged for centuries.

This is observable in many of the tributaries of the Dora Baltea, which drains the valley of Aosta. Several of these small rivers are spanned by more or less perfect Roman bridges--one of which, that over the Lys at Pont St. Martin, is still in good repair and in constant use. An examination of the rocks on which the abutments of this and some other similar structures are founded, and of the channels of the rivers they cross, shows that the beds of the streams cannot have been much elevated or depressed since the bridges were built. In other cases, as at the outlet of the Val Tournanche at Chatillon, where a single rib of a Roman bridge still remains, there is nothing to forbid the supposition that the deep excavation of the channel may have been partly effected at much later period.

The Roman aqueduct known as the Pont du Gard, near Nismes, was built, in all probability, nineteen centuries ago. The bed of the river Gardon, a rather swift stream, which flows beneath it, can have suffered but slight depression since the piers of the aqueduct were founded.]

In the inundation of 1857, the Ardeche destroyed a stone bridge near La Beaume, which had been built about eighty years before. The resistance of the piers, which were erected on piles, the channel at that point being of gravel, produced an eddying current that washed away the bed of the river above them, and the foundation, thus deprived of lateral support, yielded to the weight of the bridge, and the piles and piers fell up-stream.

By a curious law of compensation, the stream which, at flood, scoops out cavities in its bed, often fills them up again as soon as the diminished velocity of the current allows it to let fall the sand and gravel with which it is charged, so that when the waters return to their usual channel, the bottom shows no sign of having been disturbed. In a flood of the Escontay, a tributary of the Rhone, in 1846, piles driven sixteen feet into its gravelly bed for the foundation of a pier were torn up and carried off, and yet, when the river had fallen to low-water mark, the bottom at that point appeared to have been raised higher than it was before the flood, by new deposits of sand and gravel, while the cut stones of the half-built pier were found buried to a great depth in the excavation which the water had first washed out. The gravel with which rivers thus restore the level of their beds is princ.i.p.ally derived from the crus.h.i.+ng of the rocks brought down by the mountain torrents, and the destructive effects of inundations are immensely diminished by this reduction of large stones to minute fragments. If the blocks hurled down from the cliffs were transported unbroken to the channels of large rivers, the mechanical force of their movement would be irresistible.

They would overthrow the strongest barriers, spread themselves over a surface as wide as the flow of the waters, and convert the most smiling valleys into scenes of the wildest desolation.

As I have before remarked, I have taken my ill.u.s.trations of the action of torrents and mountain streams princ.i.p.ally from French authorities, because the facts recorded by them are chiefly of recent occurrence, and as they have been collected with much care and described with great fulness of detail, the information furnished by them is not only more trustworthy, but both more complete and more accessible than that which can be gathered from any other source. It is not to be supposed, however, that the countries adjacent to France have escaped the consequences of a like improvidence. The southern flanks of the Alps, and, in a less degree, the northern slope of these mountains and the whole chain of the Pyrenees, afford equally striking examples of the evils resulting from the wanton sacrifice of nature's safeguards. But I can afford s.p.a.ce for few details, and as an ill.u.s.tration of the extent of these evils in Italy, I shall barely observe that it was calculated ten years ago that four-tenths of the area of the Ligurian provinces had been washed away or rendered incapable of cultivation in consequence of the felling of the woods. [Footnote: Annali di Agricoltura, Industria e Commercio, vol. i., p. 77. Similar instances of the erosive power of running water might be collected by hundreds from the narratives of travellers in warm countries. The energy of the torrents of the Himalayas is such that the brothers Schlagintweit believe that they will cut gorges through that lofty chain wide enough to admit the pa.s.sage of currents of warm wind from the south, and thereby modify the climate of the countries lying to the north of the mountains.]

Highly colored as these pictures seem, they are not exaggerated, although the hasty tourist through Southern France, Switzerland, the Tyrol, and Northern Italy, finding little in his high-road experiences to justify them, might suppose them so. The lines of communication by locomotive-train and diligence lead generally over safer ground, and it is only when they ascend the Alpine pa.s.ses and traverse the mountain chains, that scenes somewhat resembling those just described fall under the eye of the ordinary traveller. But the extension of the sphere of devastation, by the degradation of the mountains and the transportation of their debris, is producing a.n.a.logous effects upon the lower ridges of the Alps and the plains which skirt them; and even now one needs but an hour's departure from some great thoroughfares to reach sites where the genius of destruction revels as wildly as in the most frightful of the abysses which Blanqui has painted. [Footnote: The Skalara-Tobel, for instance, near Coire. See the description of this and other like scenes in Berlepsch, Die Alpen, pp. 169 et seqq., or in Stephen's English translation.

About an hour from Thusis, on the Splagen road, "opens the awful chasm of the Nolla which a hundred years ago poured its peaceful waters through smiling meadows protected by the wooded slopes of the mountains.

But the woods were cut down and with them departed the rich pastures, the pride of the valley, now covered with piles of rock and rubbish swept down from the mountains. This result is the more to be lamented as it was entirely compa.s.sed by the improvidence of man in thinning the forests."--Morell, Scientific Guide to Switzerland, p. 100.

The recent change in the character of the Mella--a river anciently so remarkable for the gentleness of its current that it was specially noticed by Catullus as flowing molli flumine--deserves more than a pa.s.sing remark. This river rises in the mountain-chain east of Lake Iseo, and traversing the district of Brescia, empties into the Oglio after a course of about seventy miles. The iron-works in the upper valley of the Mella had long created a considerable demand for wood, but their operations were not so extensive as to occasion any very sudden or general destruction of the forests, and the only evil experienced from the clearings was the gradual diminution of the volume of the river.

Within the last thirty years, the superior quality of the arms manufactured at Brescia has greatly enlarged the sale of them, and very naturally stumulated the activity of both the forges and of the colliers who supply them, and the hillsides have been rapidly stripped of their timber. Up to 1850, no destructive inundation of the Mella had been recorded. Buildings in great numbers had been erected upon its margin, and its valley was conspicuous for its rural beauty and its fertility.

But when the denudation of the mountains had reached a certain point, avenging nature began the work of retribution. In the spring and summer of 1850 several new torrents were suddenly formed in the upper tributary valleys, and on the 14th and 15th of August in that year a fall of rain, not heavier than had been often experienced, produced a flood which not only inundated much ground never before overflowed, but destroyed a great number of bridges, dams, factories, and other valuable structures, and, what was a far more serious evil, swept off from the rocks an incredible extent of soil, and converted one of the most beautiful valleys of the Italian Alps into a ravine almost us bare and as barren as the savagest gorge of Southern France. The pecuniary damage was estimated at many millions of francs, and the violence of the catastrophe was deemed so extraordinary, even in a country subject to similar visitations, that the sympathy excited for the sufferers produced, in five months, voluntary contributions for their relief to the amount of nearly $200,000.--Delle Inondazioni del Mella, etc., nella notte del 14 al 15 Agosto, 1850.

The author of this pamphlet has chosen as a motto a pa.s.sage from the Vulgate translation of Job, which is interesting as showing accurate observation of the action of the torrent: "Mons cadens definit, et saxum transfertur de loco suo; lapides excavant aquae et alluvione paullatim terra consumitur."--Job xiv. 18, 19.

The English version is much less striking, and gives a different sense.

The recent date of the change in the character of the Mella is contested, and it is possible that, though the extent of the revolution is not exaggerated, the rapidity with which it has taken place may have been.]

There is one effect of the action of torrents which few travellers on the Continent are heedless enough to pa.s.s without notice. I refer to the elevation of the beds of mountain streams in consequence of the deposit of the debris with which they are charged. To prevent the spread of sand and gravel over the fields and the deluging overflow of the raging waters, the streams are confined by walls and embankments, which are gradually built higher and higher as the bed of the torrent is raised, so that, to reach a river, you ascend from the fields beside it; and sometimes the ordinary level of the stream is above the streets and even the roofs of the towns through which it pa.s.ses. [Footnote: Streffleur quotes from Duile the following observations: "The channel of the Tyrelese brooks is often raised much above the valleys through which they flow. The bed of the Fersina is elevated high above the city of Trent, which lies near it. The Villerbach flows at a much more elevated level than that of the market-place of Neumarkt and Vill, and threatens to overwhelm both of them with its waters. The Talfer at Botzen is at least even with the roofs of the adjacent town, if not above them. The tower-steeples of the villages of Schlanders, Kortsch, and Laas, are lower than the surface of the Gadribach. The Saldurbach at Schluderus menaces the far lower village with destruction, and the chief town, Schwaz, is in similar danger from the Lahnbach."--Streffleur, Ueber die Wildbuche, etc., p. 7.] The traveller who visits the depths of an Alpine ravine, observes the length and width of the gorge and the great height and apparent solidity of the precipitous walls which bound it, and calculates the ma.s.s of rock required to fill the vacancy, can hardly believe that the humble brooklet which purls at his feet has been the princ.i.p.al agent in accomplis.h.i.+ng this tremendous erosion. Closer observation will often teach him, that the seemingly unbroken rock which overhangs the valley is full of cracks and fissures, and really in such a state of disintegration that every frost must bring down tons of it.

If he computes the area of the basin which finds here its only discharge, he will perceive that a sudden thaw of the winter's deposit of snow, or one of those terrible discharges of rain so common in the Alps, must send forth a deluge mighty enough to sweep down the largest ma.s.ses of gravel and of rock. The simple measurement of the cubical contents of the semicircular hillock which he climbed before he entered the gorge, the structure and composition of which conclusively show that it must have been washed out of this latter by torrential action, will often account satisfactorily for the disposal of most of the matter which once filled the ravine. When a torrent escapes from the lateral confinement of its mountain walls and pours out of the gorge, it spreads and divides itself into numerous smaller streams which shoot out from the mouth of the ravine as from a centre, in different directions, like the ribs of a fan from the pivot, each carrying with it its quota of stones and gravel. The plain below the point of issue from the mountain is rapidly raised by newly-formed torrents, the elevation depending on the inclination of the bed and the form and weight of the matter transported. Every flood both increases the height of this central point and extends the entire circ.u.mference of the deposit. Other things being equal, the transporting power of the water is greatest where its flow is most rapid. This is usually in the direction of the axis of the ravine.

The stream retaining most nearly this direction moves with the greatest momentum, and consequently transports the solid matter with which it is charged to the greatest distance.

The untravelled reader will comprehend this the better when he is informed that the southern slope of the Alps generally rises suddenly out of the plain, with no intervening hill to break the abruptness of the transition, except those consisting of comparatively small heaps of its own debris brought down by ancient glaciers or recent torrents. The torrents do not wind down valleys gradually widening to the rivers or the sea, but leap at once from the flanks of the mountains upon the plains below. This arrangement of surfaces naturally facilitates the formation of vast deposits at their points of emergence, and the centre of the acc.u.mulation in the case of very small torrents is not unfrequently a hundred feet high, and sometimes very much more.

The deposits of the torrent which has scooped out the Nantzen Thal, a couple of miles below Brieg in the Valais, have built up a semicircular hillock, which most travellers by the Simplon route pa.s.s over without even noticing it, though it is little inferior in dimensions to the great cones of dejection described by Blanqui. The princ.i.p.al course of the torrent having been--I know not whether spontaneously or artificially--diverted towards the west, the eastern part of the hill has been gradually brought under cultivation, and there are many trees, fields, and houses upon it; but the larger western part is furrowed with channels diverging from the summit of the deposit at the outlet of the Nantzen Thal, which serve as the beds of the water-courses into which the torrent has divided itself. All this portion of the hillock is subject to inundation after long and heavy rain, and as I saw it in the great flood of October, 1866, almost its whole surface seemed covered with an unbrokun sheet of rus.h.i.+ng water.

The semi-conical deposit of detritus at the mouth of the Litznerthal, a lateral branch of the valley of the Adige, at the point where the torrent pours out of the gorge, is a thousand feet high and, measuring along the axis of the princ.i.p.al current, two and a half miles long.

[Footnote: Sonklar, Die Octzthaler Gebirgsgruppe, 1861, p. 231.] The solid material of this hillock--which it is hardly an exaggeration to call a mountain, the work of a single insignificant torrent and its tributaries--including what the river which washes its base has carried off in a comparatively few years, probably surpa.s.ses the ma.s.s of the stupendous pyramid of the Matterhorn. In valleys of ancient geological formation, which extend into the very heart of the mountains, the streams, though rapid, have often lost the true torrential character, if, indeed, they ever possessed it. Their beds have become approximately constant, and their walls no longer crumble and fall into the waters that wash their bases. The torrent-worn ravines, of which I have spoken, are of later date, and belong more properly to what may be called the crust of the Alps, consisting of loose rocks, of gravel, and of earth, strewed along the surface of the great declivities of the central ridge, and acc.u.mulated thickly between their solid b.u.t.tresses. But it is on this crust that the mountaineer dwells. Here are his forests, here his pastures, and the ravages of the torrent both destroy his world, and convert it into a source of overwhelming desolation to the plains below.

I do not mean to a.s.sert that all the rocky valleys of the Alps have been produced by the action of torrents resulting from the destruction of the forests. The greater, and many of the smaller channels, by which that chain is drained, owe their origin to higher causes. They are primitive fissures, ascribable to disruption in upheaval or other geological convulsion, widened and scarped, and often even polished, so to speak, by the action of glaciers during the ice period, and but little changed in form by running water in later eras.

It has been contended that all rivers which take their rise in mountains originated in torrents. These, it is said, have lowered the summits by gradual erosion, and, with the material thus derived, have formed shoals in the sea which once beat against the cliffs; then, by successive deposits, gradually raised them above the surface, and finally expanded them into broad plains traversed by gently flowing streams. If we could get back to earlier geological periods, we should find this theory often verified, and we cannot fail to see that the torrents go on at the present hour, depressing still lower the ridges of the Alps and the Apennines, raising still higher the plains of Lombardy and Provence, extending the coast still farther into the Adriatic and the Mediterranean, reducing the inclination of their own beds and the rapidity of their flow, and thus tending to become river-like in character.