The provinces of Dauphiny and Provence comprise a territory of fourteen

or fifteen thousand square miles, bounded north-west by the Isere,

north-east and east by the Alps, south by the Mediterranean, west by the

Rhone, and extending from 42 degrees to about 45 degrees of north

latitude. The surface is generally hilly and even mountainous, and

several of the peaks in Dauphiny rise above the limit of perpetual snow.

Except upon the mountain ridges, the climate, as compared with that of

the United States in the same latitude, is extremely mild. Little snow

falls, except upon the higher mountains, the frosts are light, and the

summers long, as might, indeed, be inferred from the vegetation; for in

the cultivated districts, the vine and the fig everywhere flourish; the

olive thrives as far north as 43 and one half degrees, and upon the

coast grow the orange, the lemon, and the date-palm. The forest trees,

too, are of southern type, umbrella pines, various species of evergreen

oaks, and many other trees and shrubs of persistent broad-leaved

foliage, characterizing the landscape.

The rapid slope of the mountains naturally exposed these provinces to

damage by torrents, and the Romans diminished their injurious effects by

erecting, in the beds of ravines, barriers of rocks loosely piled up,

which permitted a slow escape of the water, but compelled it to deposit

above the dikes the earth and gravel with which it was charged.

[Footnote: Whether Palissy was acquainted with this ancient practice, or

whether it was one of those original suggestions of which his works are

so full, I know not, but in his treatise, Des Eaux et Fontaines, he thus

recommends it, by way of reply to the objections of "Theorique," who had

expressed the fear that "the waters which rush violently down from the

heights of the mountain would bring with them much earth, sand, and

other things," and thus spoil the artificial fountain that "Practique"

was teaching him to make: "And for hindrance of the mischiefs of great

waters which may be gathered in a few hours by great storms, when thou

shalt have made ready thy parterre to receive the water, thou must lay

great atones athwart the deep channels which lead to thy parterre. And

so the force of the rushing currents shall be deadened, and thy water

shall flow peacefully into his cisterns."--Oeuvres Completes, p. 178.]

At a later period the Crusaders brought home from Palestine, with much

other knowledge gathered from the wiser Moslems, the art of securing the

hillsides and making them productive by terracing and irrigation. The

forests which covered the mountains secured an abundant flow of springs,

and the process of clearing the soil went on so slowly that, for

centuries, neither the want of timber and fuel, nor the other evils

about to be depicted, were seriously felt. Indeed, throughout the Middle

Ages, these provinces were well wooded, and famous for the fertility and

abundance, not only of the low grounds, but of the hills.

Such was the state of things at the close of the fifteenth century. The

statistics of the seventeenth show that while there had been an increase

of prosperity and population in Lower Provence, as well as in the

correspondingly situated parts of the other two provinces I have

mentioned, there was an alarming decrease both in the wealth and in the

population of Upper Provence and Dauphiny, although, by the clearing of

the forests, a great extent of plough-land and pasturage had been added

to the soil before reduced to cultivation. It was found, in fact, that

the augmented violence of the torrents had swept away, or buried in sand

and gravel, more land than had been reclaimed by clearing; and the taxes

computed by fires or habitations underwent several successive reductions

in consequence of the gradual abandonment of the wasted soil by its

starving occupants. The growth of the large towns on and near the Rhone

and the coast, their advance in commerce and industry, and the

consequently enlarged demand for agricultural products, ought naturally

to have increased the rural population and the value of their lands; but

the physical decay of the uplands was such that considerable tracts were

deserted altogether, and in Upper Provence, the fires which, in 1471

counted 897, were reduced to 747 in 1699, to 728 in 1733, and to 635 in

1776. [Footnote: These facts I take from the La Provence au point de vue

des Bois, des Torrents et des Inondations, of Charles de Ribbe, one of

the highest authorities.]

Surell--whose admirable work, Etude sur les Torrents des Hautes Alpes,

first published in 1841, [Footnote: A second edition of this work, with

an additional volume of great value by Ernest Cezanne, was published at

Paris, in two 8vo volumes, in 1871-72.] presents a most appalling

picture of the desolations of the torrent, and, at the same time, the

most careful studies of the history and essential character of this

great evil--in speaking of the valley of Devoluy, on page 152, says:

"Everything concurs to show that it was anciently wooded. In its

peat-bogs are found buried trunks of trees, monuments of its former

vegetation. In the framework of old houses, one sees enormous timber,

which is no longer to be found in the district. Many localities, now

completely bare, still retain the name of 'wood,' and one of them is

called, in old deeds, Comba nigra [Black forest or dell], on account of

its dense woods. These and many other proofs confirm the local

traditions which are unanimous on this point.

"There, as everywhere in the Upper Alps, the clearings began on the

flanks of the mountains, and were gradually extended into the valleys

and then to the highest accessible peaks. Then followed the Revolution,

and caused the destruction of the remainder of the trees which had thus

far escaped the woodman's axe."

In a note to this passage the writer says: "Several persons have told me

that they had lost flocks of sheep, by straying, in the forests of Mont

Auroux, which covered the flanks of the mountain from La Cluse to

Agneres. These declivities are now as bare as the palm of the hand."

The ground upon the steep mountains being once bared of trees, and the

underwood killed by the grazing of horned cattle, sheep, and goats,

every depression becomes a water-course. "Every storm," says Surell,

page 153, "gives rise to a new torrent. [Footnote: No attentive observer

can frequent the southern flank of the Piedmontese Alps or the French

province of Dauphiny, for half a dozen years, without witnessing with

his own eyes the formation and increase of new torrents. I can bear

personal testimony to the conversion of more than one grassy slope into

the bed of a furious torrent by baring the hills above of their woods.]

Examples of such are shown, which, though not yet three years old, have

laid waste the finest fields of their valleys, and whole villages have

narrowly escaped being swept into ravines formed in the course of a few

hours. Sometimes the flood pours in a sheet over the surface, without

ravine or even bed, and ruins extensive grounds, which are abandoned

forever."

I cannot follow Surell in his description and classification of

torrents, and I must refer the reader to his instructive work for a full

exposition of the theory of the subject. In order, however, to show what

a concentration of destructive energies may be effected by felling the

woods that clothe and support the sides of mountain abysses, I cite his

description of a valley descending from the Col Isoard, which he calls

"a complete type of a basin of reception," that is, a gorge which serves

as a common point of accumulation and discharge for the waters of

several lateral torrents. "The aspect of the monstrous channel," says

he, "is frightful. Within a distance of less than two English miles,

more than sixty torrents hurl into the depths of the gorge the debris

torn from its two flanks. The smallest of these secondary torrents, if

transferred to a fertile valley, would be enough to ruin it."

The eminent political economist Blanqui, in a memoir read before the

Academy of Moral and Political Science on the 25th of November, 1843,

thus expresses himself: "Important as are the causes of impoverishment

already described, they are not to be compared to the consequences which

have followed from the two inveterate evils of the Alpine provinces of

France, the extension of clearing and the ravages of torrents. ... The

most important result of this destruction is this; that the agricultural

capital, or rather the ground itself--which, in a rapidly increasing

degree, is daily swept away by the waters--is totally lost. Signs of

unparalleled destitution are visible in all the mountain zone, and the

solitudes of those districts are assuming an indescribable character of

sterility and desolation. The gradual destruction of the woods has, in a

thousand localities, annihilated at once the springs and the fuel.

Between Grenoble and Briancon, in the valley of the Romanche, many

villages are so destitute of wood that they are reduced to the necessity

of baking their bread with sun-dried cow-dung, and even this they can

afford to do but once a year.

"Whoever has visited the valley of Barcelonette, those of Embrun, and of

Verdun, and that Arabia Petraea of the department of the Upper Alps,

called Devoluy, knows that there is no time to lose--that in fifty years

from this date France will be separated from Savoy, as Egypt from Syria,

by a desert." [Footnote: Ladoucette says the peasant of Devoluy "often

goes a distance of five hours over rocks and precipices for a single

[man's] load of wood;" and he remarks on another page, that "the justice

of peace of that canton had, in the course of forty-three years, but

once heard the voice of the nightingale."--Histoire, etc, des Hautes

Alpes, pp. 220, 434.]

It deserves to be specially noticed that the district here referred to,

though now among the most hopelessly waste in France, was very

productive even down to so late a period as the commencement of the

French Revolution. Arthur Young, writing in 1789, says: "About

Barcelonette and in the highest parts of the mountains, the

hill-pastures feed a million of sheep, besides large herds of other

cattle;" and he adds: "With such a soil and in such a climate, we are

not to suppose a country barren because it is mountainous. The valleys I

have visited are, in general, beautiful." [Footnote: The valley of

Embrun, now almost completely devastated, was once remarkable for its

fertility. In 1800, Hericart de Thury said of it: "In this magnificent

valley nature had been prodigal of her gifts. Its inhabitants have

blindly revelled in her favors, and fallen asleep in the midst of her

profusion."--Becquerel, Des Climats, etc., p. 314.] He ascribes the same

character to the provinces of Dauphiny, Provence, and Auvergne, and,

though he visited, with the eye of an attentive and practised observer,

many of the scenes since blasted with the wild desolation described by

Blanqui, the Durance and a part of the course of the Loire are the only

streams he mentions as inflicting serious injury by their floods. The

ravages of the torrents had, indeed, as we have seen, commenced earlier

in some other localities, but we are authorized to infer that they were,

in Young's time, too limited in range, and relatively too insignificant,

to require notice in a general view of the provinces where they have now

ruined so large a proportion of the soil.

But I resume my citations.

"I do not exaggerate," says Blanqui. "When I shall have finished my

description and designated localities by their names, there will rise, I

am sure, more than one voice from the spots themselves, to attest the

rigorous exactness of this picture of their wretchedness. I have never

seen its equal even in the Kabyle villages of the province of

Constantine; for there you can travel on horseback, and you find grass

in the spring, whereas in more than fifty communes in the Alps there is

absolutely nothing.

"The clear, brilliant, Alpine sky of Embrun, of Gap, of Barcelonette,

and of Digne, which for months is without a cloud, produces droughts

interrupted only by diluvial rains like those of the tropics. The abuse

of the right of pasturage and the felling of the woods have stripped the

soil of all its grass and all its trees, and the scorching sun bakes it

to the consistence of porphyry. When moistened by the rain, as it has

neither support nor cohesion, it rolls down to the valleys, sometimes in

floods resembling black, yellow, or reddish lava, sometimes in streams

of pebbles, and over huge blocks of stone, which pour down with a

frightful roar, and in their swift course exhibit the most convulsive

movements. If you overlook from an eminence one of these landscapes

furrowed with so many ravines, it presents only images of desolation and

of death. Vast deposits of flinty pebbles, many feet in thickness, which

have rolled down and spread far over the plain, surround large trees,

bury even their tops, and rise above them, leaving to the husbandman no

longer a ray of hope. One can imagine no sadder spectacle than the deep

fissures in the flanks of the mountains, which seem to have burst forth

in eruption to cover the plains with their ruins. Those gorges, under

the influence of the sun which cracks and shivers to fragments the very

rocks, and of the rain which sweeps them down, penetrate deeper and

deeper into the heart of the mountain, while the beds of the torrents

issuing from them are sometimes raised several feet in a single year, by

the debris, so that they reach the level of the bridges, which, of

course, are then carried off. The torrent-beds are recognized at a great

distance, as they issue from the mountains, and they spread themselves

over the low grounds, in fan-shaped expansions, like a mantle of stone,

sometimes ten thousand feet wide, rising high at the centre, and curving

towards the circumference till their lower edges meet the plain.

"Such is their aspect in dry weather. But no tongue can give an adequate

description of their devastations in one of those sudden floods winch

resemble, in almost none of their phenomena, the action of ordinary

river-water. They are now no longer overflowing brooks, but real seas,

tumbling down in cataracts, and rolling before them blocks of stone,

which are hurled forwards by the shock of the waves like balls shot out

by the explosion of gunpowder. Sometimes ridges of pebbles are driven

down when the transporting torrent does not rise high enough to show

itself, and then the movement is accompanied with a roar louder than the

crash of thunder. A furious wind precedes the rushing water and

announces its approach. Then comes a violent eruption, followed by a

flow of muddy waves, and after a few hours all returns to the dreary

silence which at periods of rest marks these abodes of desolation.

[Footnote: These explosive gushes of mud and rock appear to be

occasioned by the caving-in of large masses of earth from the banks of

the torrent, which dam up the stream and check its flow until it has

acquired volume enough to burst the barrier and carry all before it. In

1827, such a sudden eruption of a torrent, after the current had

appeared to have ceased, swept off forty-two houses and drowned

twenty-eight persons in the village of Goncelin, near Grenoble, and

buried with rubbish a great part of the remainder of the village."

The French traveller, D'Abbadie, relates precisely similar occurrences

as not unfrequent in the mountains of Abyssinia.--Surrell, Etudes, etc;

2d edition, pp. 224, 295.]

"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, masses of water suddenly shoot from the mountain heights

into the shattered gulfs, waste without irrigating, deluge without

refreshing 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 passages 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 diminishing 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 grass 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 passion 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 principal 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 Chassezac, 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 Chassezac. 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

quantity of water passing 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 passage in

question amounted to more than 450,000,000 cubic yards. This quantity,

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 washing 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 quantity 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 titan in many other parts of Europe, but excessive quantities 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

Grenoble, has discharged 5,200, the Isere, which receives it, 7,800

cubic yards, and the Durance, above its junction with the Isere, an

equal quantity, 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 quantity.]

The Rhone, therefore, is naturally subject to great and sudden

inundations, and the same remark may be applied to most of the principal

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 principally 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, Analisi 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 principally 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 accumulations 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 principally derived from

the crushing 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 illustrations of the action

of torrents and mountain streams principally 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 space for few details, and as an illustration 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 passage 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 passes 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 analogous 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 compassed 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

passing 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 passage 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 pass 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 passes. [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 mass of rock required to fill the vacancy, can hardly

believe that the humble brooklet which purls at his feet has been the

principal agent in accomplishing 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

masses 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 circumference 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 accumulation 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 pass over without

even noticing it, though it is little inferior in dimensions to the

great cones of dejection described by Blanqui. The principal 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 rushing 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 principal 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 surpasses the mass 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 accumulated thickly between their solid buttresses. 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 assert 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.

We cannot measure the share which human action has had in augmenting the

intensity of causes of mountain degradation, and of the formation of

plains and marshes below, but we know that the clearing of the woods

has, in some cases, produced, within two or three generations, effects

as blasting as those generally ascribed to geological convulsions, and

has laid waste the face of the earth more hopelessly than if it had been

buried by a current of lava or a shower of volcanic sand. New torrents

are forming every year in the Alps. Tradition, written records, and

analogy concur to establish the belief that the ruin of most of the now

desolate valleys in those mountains is to be ascribed to the same cause,

and authentic descriptions of the irresistible force of the torrent show

that, aided by frost and heat, it is adequate to level Mont Blanc and

Monte Rosa themselves, unless new upheavals shall maintain their

elevation.

There are cases where torrents cease their ravages of themselves, in

consequence of some change in the condition of the basin where they

originate, or of the face of the mountain at a higher level, while the

plain or the sea below remains in substantially the same state as

before. If a torrent rises in a small valley containing no great amount

of earth and of disintegrated or loose rock, it may, in the course of a

certain period, wash out all the transportable material, and if the

valley is then left with solid walls, it will cease to furnish debris to

be carried down by floods. If, in this state of things, a new channel be

formed at an elevation above the head of the valley, it may divert a

part or even the whole of the rain-water and melted snow which would

otherwise have flowed into it, and the once furious torrent now sinks to

the rank of a humble and harmless brooklet. "In traversing this

department," says Suroll, "one often sees, at the outlet of a gorge, a

flattened hillock, with a fan-shaped outline and regular slopes; it is

the bed of dejection of an ancient torrent. It sometimes requires long

and careful study to detect the primitive form, masked as it is by

groves of trees, by cultivated fields, and often by houses, but, when

examined closely, and from different points of view, its characteristic

figure manifestly appears, and its true history cannot be mistaken.

Along the hillock flows a streamlet, issuing from the ravine, and

quietly watering the fields. This was originally a torrent, and in the

background may be discovered its mountain basin. Such EXTINGUISHED

torrents, if I may use the expression, are numerous." [Footnote: Surrell,

Les Torrents des Hautes Alpes, chap. xxiv. In such cases, the clearing

of the ground, which, in consequence of a temporary diversion of the

waters, or from some other cause, has become rewooded, sometimes renews

the ravages of the torrent. Thus, on the left bank of the Durance, a

wooded declivity had been formed by the debris brought down by torrents,

which had extinguished themselves after having swept off much of the

superficial strata of the mountain of Morgon. "All this district was

covered with woods, which have now been thinned out and are perishing

from day to day; consequently, the torrents have recommenced their

devastations, and if the clearings continue, this declivity, now

fertile, will he ruined, like so many others."--Ibid, p. 155.]

But for the intervention of man and domestic animals, these latter

beneficent revolutions would occur more frequently, proceed more

rapidly. The new scarped mountains, the hillocks of debris, the plains

elevated by sand and gravel spread over them, the shores freshly formed

by fluviatile deposits, would clothe themselves with shrubs and trees,

the intensity of the causes of degradation would be diminished, and

nature would thus regain her ancient equilibrium. But these processes,

under ordinary circumstances, demand, not years, generations, but

centuries; [Footnote: Where a torrent has not been long in operation, and

earth still remains mixed with the rocks and gravel it heaps up at its

point of eruption, vegetation soon starts up and prospers, it protected

from encroachment. In Provence, "several communes determined, about ten

years ago, to reserve the soils thus wasted, that is, to abandon them

for a certain time, to spontaneous vegetation, which was not slow in

making its appearance."-Becquerel, Des Climats, p. 815.] and man, who

even now finds scarce breathing-room on this vast globe, cannot retire

from the Old World to some yet undiscovered continent, and wait for the

slow action of such causes to replace, by a new creation, the Eden he

has wasted.

Crushing Force of Torrents.

I must here notice a mechanical effect of the rapid flow of the torrent,

which is of much importance in relation to the desolating action it

exercises by covering large tracts of cultivated ground with infertile

material. The torrent, as we have seen, shoots or rolls forwards, with

great velocity, masses and fragments of rock, and sometimes rounded

pebbles from more ancient formations. Every inch of this violent

movement is accompanied with crushing concussion, or, at least, with

great abrasion of the mineral material, and, as you follow it along the

course of the waters which transport it, you find the stones gradually

rounding off in form, and diminishing in size, until they pass

successively into gravel, and, in the beds of the rivers to which the

torrents convey it, sand, and lastly impalpable slime.

There are few operations of nature where the effect seems more

disproportioned to the cause than in the crushing and comminution of

rock in the channel of swift waters. Igneous rocks are generally so hard

as to be wrought with great difficulty, and they bear the weight of

enormous superstructures without yielding to the pressure; but to the

torrent they are as wheat to the millstone. The streams which pour down

the southern scarp of the Mediterranean Alps along the Riviera di

Ponente, near Genoa, have short courses, and a brisk walk of a couple of

hours or even less takes you from the sea-beach to the headspring of

many of them. In their heaviest floods, they bring rounded masses of

serpentine quite down to the sea, but at ordinary high water their lower

course is charged only with finely divided particles of that rock.

Hence, while, near their sources, their channels are filled with pebbles

and angular fragments, intermixed with a little gravel, the proportions

are reversed near their months, and, just above the points where their

outlets are partially choked by the rolling shingle of the beach, their

beds are composed of sand and gravel to the almost total exclusion of

pebbles.

Guglielmini argued that the gravel and sand of the beds of running

streams were derived from the trituration of rocks by the action of the

currents, and inferred that this action was generally sufficient to

reduce hard rock to sand in its passage from the source to the outlet of

rivers. Frisi controverted this opinion, and maintained that river-sand

was of more ancient origin, and he inferred from experiments in

artificially grinding stones that the concussion, friction, and

attrition of rock in the channel of running waters were inadequate to

its comminution, though he admitted that these same causes might reduce

silicious sand to a fine powder capable of transportation to the sea by

the currents. [Footnote: Frisi, Del modo di regolare i Fiumi e i

Torrenti, pp. 4-19. See in Lombardini, Sulle Inondazioni in Francia, p.

87, notices of the action of currents transporting only fine material in

wearing down hard rock. In the sluices for gold-washing in California

having a grade of 1 to 14 1/2, and paved with the hardest stones, the

wear of the bottom is at the rate of two inches in three

months.--Raymond, Mineral Statistics, 1870, p. 480.] Frisi's experiments

were tried upon rounded and polished river-pebbles, and prove nothing

with regard to the action of torrents upon the irregular, more or less

weathered, and often cracked and shattered rocks which lie loose in the

ground at the head of mountain valleys. The fury of the waters and of

the wind which accompanies them in the floods of the French Alpine

torrents is such, that large blocks of stone are hurled out of the bed

of the stream to the height of twelve or thirteen feet. [Footnote:

Surrell, Etude sur les Torrents, pp. 81-86.] The impulse of masses

driven with such force overthrows the most solid masonry, and their

concussion cannot fail to be attended with the crushing of the rocks

themselves.

The greatest depth of the basin of the Ardeche is seventy-five miles,

but most of its tributaries have a much shorter course. "These

affluents," says Mardigny, "hurl into the bed of the Ardeche enormous

blocks of rock, which this river, in its turn bears onwards, and grinds

down, at high water, so that its current rolls only gravel at its

confluence with the Rhone." [Footnote: At Rinkenberg, on the right bank

of the Vorder Rhein, in the flood of 1868, a block of stone computed to

weigh nearly 9,000 cwt. was carried bodily forwards, not rolled, by a

torrent, a distance of three-quarter of a mile.--Coaz, die Hochwasser im

1868, p. 54.

Memoire sur les Inondations des Rivieres de l'Ardeche, p. 16. "The

terrific roar, the thunder of the raging torrents proceeds principally

from the stones which are rolled along in the bed of the stream. This

movement is attended with such powerful attrition that, in the Southern

Alps, the atmosphere of valleys where the limestone contains bitumen,

has, at the time of floods, the marked bituminous smell produced by

rubbing pieces of such limestone together."--Wessely, Die

Oesterreichischen Alpenlander, i., p. 113.] Duponchel makes the

following remarkable statement: "The river Herault rises in a granitic

region, but soon reaches calcareous formations, which it traverses for

more than sixty kilometres, rolling through deep and precipitous

ravines, into which the torrents are constantly discharging enormous

masses of pebbles belonging to the hardest rocks of the Jurassian

period. These debris, continually renewed, compose, even below the exit

of the gorge where the river enters into a regular channel cut in a

tertiary deposit, broad beaches, prodigious accumulations of rolled

pebbles, extending several kilometres down the stream, but they diminish

in size and weight so rapidly that above the mouth of the river, which

is at a distance of thirty or thirty-five kilometres from the gorge,

every trace of calcareous matter has disappeared from the sands of the

bottom, which are exclusively silicious." [Footnote: Avant-projet pour

la creation d'un sol fertile, p. 20.]

Similar effects of the rapid flow of water and the concussion of stones

against each other in river-beds may be observed in almost every Alpine

gorge which serves as the channel of a swift stream. The tremendous

cleft through which the well-known Via Mala is carried receives, every

year, from its own crumbling walls and from the Hinter Rhein and its

mild tributaries, enormous quantities of rock, in blocks and boulders.

In fact, the masses hurled into it in a single flood like those of 1868

would probably fill it up, at its narrow points, to the

level of the road 400 feet above its bottom, were not the stones crushed

and carried off by the force of the current. Yet below the outlet at

Thusis only small rounded boulders, pebbles, and gravel, not rock, are

found in the bed of the river. The Swiss glaciers bring down thousands

of cubic yards of hard rock every season. Where the glacier ends in a

plain or wide valley, the rocks are accumulated in a terminal moraine,

but in numerous instances the water which pours from the ice-river has

forces enough to carry down to larger streams the masses delivered by

the glacier, and there they, with other stones washed out from the earth

by the current, are ground down, so that few of the affluents of the

Swiss lakes deliver into them anything but fine sand and slime. Great

rivers carry no boulders to the sea, and, in fact, receive none from

their tributaries. Lombardini found, twenty years ago, that the mineral

matter brought down to the Po by its tributaries was, in general,

comminuted to about the same degree of fineness as the sands of its bed

at their points of discharge. In the case of the Trebbia, which rises

high in the Apennines and empties into the Po at Piacenza, it was

otherwise, that river rolling pebbles and coarse gravel into the channel

of the principal stream. The banks of the other affluents--excepting

some of those which discharge their waters into the great lakes--then

either retained their woods, or had been so long clear of them that the

torrents had removed most of the disintegrated and loose rock in their

upper basins. The valley of the Trebbia had been recently cleared, and

all the forces which tend to the degradation and transportation of rock

were in full activity. [Footnote: Since the date of Lombardini's

observations, many Alpine valleys have been stripped of their woods. It

would be interesting to know whether any sensible change has been

produced in the character or quantity of the matter transported by the

rivers to the Po.--Notice sur les Rivieres de la Lombardie, Annales des

Ponts et Chaussees, 1847, 1er semestre, p. 131.]

Transporting Power of Water.

But the geographical effects of the action of torrents are not confined

to erosion of earth and comminution of rock; for they and the rivers to

which they contribute transport the debris of the mountains to lower

levels and spread them out over the dry land and the bed of the sea,

thus forming alluvial deposits, sometimes of a beneficial, sometimes of

an injurious, character, and of vast extent. [Footnote: Lorentz, in an

official report quoted by Marchand, says: "The felling of the woods

produces torrents which cover the cultivated soil with pebbles and

fragments of rock, and they do not confine their ravages to the vicinity

of the mountains, but extend them into the fertile fields of Provence

and other departments, to the distance of forty or fifty

leagues."--Entwaldung der Gebirge, p. 17.]

A mountain rivulet swollen by rain or melted snow, when it escapes from

its usual channel and floods the adjacent fields, naturally deposits

pebbles and gravel upon them; but even at low water, if its course is

long enough for its grinding action to have full scope, it transports

the solid material with which it is charged to some larger stream, and

there lets it fall in a state of minute division, and at last the spoil

of the mountain is used to raise the level of the plains or carried down

to the sea.

An instance that fell under my own observation, in 1857, will serve to

show something of the eroding and transporting power of streams which,

in these respects, fall incalculably below the torrents of the Alps. In

a flood of the Ottaquechee, a small river which flows through Woodstock,

Vermont, a mill-dam on that stream burst, and the sediment with which

the pond was filled, estimated after careful measurement at 13,000 cubic

yards, was carried down by the current. Between this dam and the

slackwater of another, four miles below, the bed of the stream, which is

composed of pebbles interspersed in a few places with larger stones, is

about sixty-five feet wide, though, at low water, the breadth of the

current is considerably less. The sand and fine gravel were smoothly and

evenly distributed over the bed to a width of fifty-five or sixty feet,

and, for a distance of about two miles, except at two or three

intervening rapids, filled up all the interstices between the stones,

covering them to the depth of nine or ten inches, so as to present a

regularly formed concave channel, lined with sand, and reducing the

depth of water, in some places, from five or six feet to fifteen or

eighteen inches. Observing this deposit after the river had subsided and

become so clear that the bottom could be seen, I supposed that the next

flood would produce an extraordinary erosion of the banks and some

permanent changes in the channel of the stream, in consequence of the

elevation of the bed and the filling up of the spaces between the stones

through which formerly much water had flowed; but no such result

followed. The spring freshet of the next year entirely washed out the

sand its predecessor had left, deposited some of it in ponds and

still-water reaches below, carried the residue beyond the reach of

observation, and left the bed of the river almost precisely in its

former condition, though, of course, with the displacement of the

pebbles which every flood produces in the channels of such streams. The

pond, though often previously discharged by the breakage of the dam, had

then been undisturbed for about twenty-five years, and its contents

consisted almost entirely of sand, the rapidity of the current in floods

being such that it would let fall little lighter sediment, even above an

obstruction like a dam. The quantity I have mentioned evidently bears a

very inconsiderable proportion to the total erosion of the stream during

that period, because the wash of the banks consists chiefly of fine

earth rather than of sand, and after the pond was once filled, or nearly

so, even this material could no longer be deposited in it. The fact of

the complete removal of the deposit I have described between the two

dams in a single freshet, shows that, in spite of considerable

obstruction from roughness of bed, large quantities of sand may be taken

up and carried off by streams of no great rapidity of inclination; for

the whole descent of the bed of the river between the two dams--a

distance of four miles--is but sixty feet, or fifteen feet to the mile.

[Footnote: In a sheet-iron siphon, 1,000 feet long, with a diameter of

four inches, having the entrance 18 feet, the orifice of discharge 40

feet below the summit of the curve, employed in draining a mine In

California, the force of the current was such as to carry through the

tube great quantities of sand and coarse gravel, some of the grains of

which were as large as an English walnut. --Raymond, Mining Statistics,

1870, p. 602.] The facts which I have adduced may aid us in forming an

idea of the origin and mode of transportation of the prodigious deposits

at the mouth of great rivers like the Mississippi, the Nile, the Ganges,

and the Hoang-Ho, the delta of which last river, composed entirely of

river sediment, has a superficial extent of not less than 96,500 square

miles. But we shall obtain a clearer conception of the character of this

important geographical process by measuring, more in detail, the mass of

earth and rock which a well--known river and its tributaries have washed

from the mountains and transported to the plains or the sea, within the

historic period.

The Po and its Deposits.

The current of the River Po, for a considerable distance after its

volume of water is otherwise sufficient for continuous navigation, is

too rapid for that purpose until near Cremona, where its velocity

becomes too much reduced to transport great quantities of mineral

matter, except in a state of minute division. Its southern affluents

bring down from the Apennines a large quantity of fine earth from

various geological formations, while its Alpine tributaries west of the

Ticino are charged chiefly with rock ground down to sand or gravel. The

bed of the river has been somewhat elevated by the deposits in its

channel, though not by any means above the level of the adjacent plains

as has been so often represented. The dikes, which confine the current

at high water, at the same time augment its velocity and compel it to

carry most of its sediment to the Adriatic. It has, therefore, raised

neither its own channel nor its alluvial shores, as it would have done

if it had remained unconfined. But, as the surface of the water in

floods is above the general level of the plains through which it flows,

the Po can, at that period, receive no contributions of earth from the

washing of the fields of Lombardy, and there is no doubt that a large

proportion of the sediment it now deposits at its mouth descended from

the Alps in the form of rock, though reduced by the grinding action of

the waters, in its passage seaward, to the condition of fine sand, and

often of silt.

We know little of the history of the Po, or of the geography of the

coast near the point where it enters the Adriatic, at any period more

than twenty centuries before our own. Still less can we say how much of

the plains of Lombardy had been formed by its action, combined with

other causes, before man accelerated its levelling operations by felling

the first woods on the mountains whence its waters are derived. But we

know that since the Roman conquest of Northern Italy, its deposits have

amounted to a quantity which, if recemented into rock, recombined into

gravel, common earth, and vegetable mould, and restored to the

situations where eruption or upheaval originally placed or vegetation

deposited it, would fill up hundreds of deep ravines in the Alps and

Apennines, change the plan and profile of their chains, and give their

southern and northern faces respectively a geographical aspect very

different from that they now present. Ravenna, forty miles south of the

principal mouth of the Po, was built like Venice, in a lagoon, and the

Adriatic still washed its walls at the commencement of the Christian

era. The mud of the Po has filled up the lagoon, and Ravenna is now four

miles from the sea. The town of Adria, which lies between the Po and the

Adige, at the distance of some four or five miles from each, was once a

harbor famous enough to have given its name to the Adriatic Sea, and it

was still accessible to large vessels, if not by the open sea at least

by lagoons, in the time of Augustus. The combined action of the two

rivers has so advanced the coast-line that Adria is now more than

fourteen miles inland, and, in other places, the deposits made within

the same period by these and other neighboring streams have a width of

twenty miles.

What proportion of the earth with which they are charged these rivers

have borne out into deep water, during the last two thousand years, we

do not know, but as they still transport enormous quantities, as the

North Adriatic appears to have shoaled rapidly, and as long islands,

composed in great part of fluviatile deposits, have formed opposite

their mouths, it must evidently have been very great. The floods of the

Po occur but once, or sometimes twice, in a year. [Footnote: In the

earlier medieval centuries, when the declivities of the mountains still

retained a much larger proportion of their woods, the moderate annual

floods of the Po were occasioned by the melting of the snows on the

lower slopes, and, according to a passage of Tasso quoted by Castellani

(Dell' Influenza delle Selve, i., p. 58, note), they took place in May.

The usually more violent inundations of later ages are due to rains, the

waters of which are no longer retained by a forest-soil, but conveyed at

once to the rivers--and they occur almost uniformly in the autumn or

late summer. Castellani, on the page just quoted, says that even so late

as about 1780, the Po required a heavy rain of a week to overflow its

banks, but that forty years later it was sometimes raised to full flood

in a single day. Pliny says: "The Po, which is inferior to no river in

swiftness of current, is in flood about the rising of the dog-star, the

snow then melting, and though so rapid in flow, it washes nothing from

the soil, but leaves it increased in fertility."--Natural History, Book

iii, 20.

The first terrible inundation of the Po in 1872 took place in May, and

appears to have been occasioned by heavy rains on the southern flank of

the Alps, and to have received little accession from snow. The snow on

the higher Alps does not usually thaw so as to occasion floods before

August, and often considerably later. The more destructive flood of

October, 1872, was caused both by thaws in the high mountains and by an

extraordinary fall of rain. See River Embankments; post. Pliny's remark

as to enrichment of the soil by the floods appear to be verified in the

case of that of October, 1872, for it is found that the water has left

very extensively a thick deposit of slime on the fields. See a list of

the historically known great inundations of the Po by the engineer

Zuccholli in Torelli, Progetto di Legge per la Vendita di Beni incolti.

Roma, 1873.]

At other times, its waters are comparatively limpid and seem to hold no

great amount of mud or fine sand in mechanical suspension; but at high

water it contains a large proportion of solid matter, and, according to

Lombardini, it annually transports to the shores of the Adriatic not

less than 42,760,000 cubic metres, or very nearly 55,000,000 cubic

yards, which carries the coast-line out into the sea at the rate of more

than 200 feet in a year. [Footnote: This change of coast-line cannot be

ascribed to upheaval, for a comparison of the level of old

buildings--as, for instance, the church of San Vitale and the tomb of

Theodoric at Ravenna--with that of the sea, tends to prove a depression

rather than an elevation of their foundations. A computation by a

different method makes the deposits at the mouth of the Po 2,123,000

metres less; but as both of them omit the gravel and silt carried down

at ordinary and low water, we are safe in assuming the larger quantity.]

The depth of the annual deposit is stated at eighteen centimetres, or

rather more than seven inches, and it would cover an area of not much

less than ninety square miles with a layer of that thickness. The Adige,

also, brings every year to the Adriatic many million cubic yards of

Alpine detritus, and the contributions of the Brenta from the same

source are far from inconsiderable. The Adriatic, however, receives but

a small proportion of the soil and rock washed away from the Italian

slope of the Alps and the northern declivity of the Apennines by

torrents. Nearly the whole of the debris thus removed from the southern

face of the Alps between Monte Rosa and the sources of the Adda--a

length of watershed [Footnote: Sir John F. W. Herschel (Physical

Geography, 137, and elsewhere) spells this word water-sched, because he

considers it a translation, or rather an adoption, of the German

"Wasser-scheide, separation of the waters, not water-SHED the slope DOWN

WHICH the waters run." As a point of historical etymology, it is

probable that the word in question was suggested to those who first used

it by the German Wasserscheide; but the spelling WATER-SCHED, proposed

by Herschel, is objectionable, both because SCH is a combination of

letters wholly unknown to modern English orthography, and properly

representing no sound recognized in English orthoepy, and for the still

better reason that WATER-SHED, in the sense of DIVISION-OF-THE-WATERS,

has a legitimate English etymology. The Anglo-Saxon sceadan meant both

to separate or divide, and to shade or shelter. It is the root of the

English verbs TO SHED and TO SHADE, and in the former meaning is the A.

S. equivalent of the German verb scheiden. SHED in Old English had the

meaning to SEPARATE or DISTINGUISH. It is so used in the Owl and the

Nightingale, v. 107. Palsgrave (Lesclarcissement, etc., p. 717) defines

I SHEDE, I departe thinges asonder; and the word still means TO DIVIDE

in several English local dialects. Hence, watershed, the division or

separation of the waters, is good English both in etymology and in

spelling.] not less than one hundred and fifty miles--is arrested by the

still waters of the Lakes Maggiore and Como, and some smaller lacustrine

reservoirs, and never reaches the sea. The Po is not continuously

embanked except for the lower half of its course. Above Cremona,

therefore, it spreads and deposits sediment over a wide surface, and the

water withdrawn from it for irrigation at lower points, as well as its

inundations in the occasional ruptures of its banks, carry over the

adjacent soil a large amount of slime. [Footnote: The quantity of

sediment deposited by the Po on the plains which border it, before the

construction of the continuous dikes and in the floods which

occasionally burst through them, is vast, and the consequent elevation

of those plains is very considerable. I do not know that this latter

point has been made a subject of special investigation, but vineyards,

with the vines still attached to the elms which supported them, have

been found two or three yards below the present surface at various

points on the plains of Lombardy.]

If to the estimated annual deposits of the Po at its mouth, we add the

earth and sand transported to the sea by the Adige, the Brenta, and

other less important streams, the prodigious mass of detritus swept into

Lago Maggioro by the Tosa, the Maggia, and the Ticino, into the lake of

Como by the Maira and the Adda, into the lakes of Garda, Lugano, Iseo,

and Idro, by their affluents, [Footnote: The Po receives about

four-tenths of its waters from these lakes. See Lombardini, Dei

cangiamenti nella condizione del Po, p. 29. All the sediment carried

into the lakes by their tributaries is deposited in them, and the water

which flows out of them is perfectly limpid. From their proximity to the

Alps and the number of torrents which empty into them, they no doubt

receive vastly more transported matter than is contributed to the Po by

the six-tenths of its waters received from other sources.] and the yet

vaster heaps of pebbles, gravel, and earth permanently deposited by the

torrents near their points of eruption from mountain gorges, or spread

over the wide plains at lower levels, we may safely assume that we have

an aggregate of not less than ten times the quantity carried to the

Adriatic by the Po, or 550,000,000 cubic yards of solid matter,

abstracted every year from the Italian Alps and the Apennines, and

removed out of their domain by the force of running water. [Footnote:

Mengotti estimated the mass of solid matter annually "united to the

waters of the Po" at 822,000,000 cubic metres, or nearly twenty times as

much as, according to Lombardini, that river delivers into the Adriatic.

Castellani supposes the computation of Mengotti to fall much below the

truth, and there can be no doubt that a vastly larger quantity of earth

and gravel is washed down from the Alps and the Apennines than is

carried to the sea.--Castellani, Dell Immediata Influenza delle Salce

sul corso delle Acqua, i., pp. 42,43.

I have contented myself with assuming less than one-half of Mengotti's

estimate.] The present rate of deposit at the mouth of the Po has

continued since the year 1600, the previous advance of the coast, after

the year 1200, having been only one-third as rapid. The great increase

of erosion and transport is ascribed by Lombardini chiefly to the

destruction of the forests in the basin of that river and the valleys of

its tributaries, since the beginning of the seventeenth century.

[Footnote: Baumgarten, An. des Ponts et Chaussees, 1847, 1er semestre,

p. 175.] We have no data to show the rate of deposit in any given

century before the year 1200, and it doubtless varied according to the

progress of population and the consequent extension of clearing and

cultivation. The transporting power of torrents is greatest soon after

their formation, because at that time their points of delivery are

lower, and, of course, their general slope and velocity more rapid, than

after years of erosion above, and deposit below, have depressed the beds

of their mountain valleys, and elevated the channels of their lower

course. Their eroding action also is most powerful at the same period,

both because their mechanical force is then greatest, and because the

loose earth and stones of freshly cleared forest-ground are most easily

removed. Many of the Alpine valleys west of the Ticino--that of the Dora

Baltea, for instance--were nearly stripped of their forests in the days

of the Roman Empire, others in the Middle Ages, and, of course, there

must have been, at different periods before the year 1200, epochs when

the erosion and transportation of solid matter from the Alps and the

Apennines were at least as great as since the year 1600.

Upon the whole, we shall not greatly err if we assume that, for a period

of not less than two thousand years, the walls of the basin of the

Po--the Italian slope of the Alps, and the northern and north-eastern

declivities of the Apennines--have annually sent down into the lakes,

the plains, and the Adriatic, not less than 375,000,000 cubic yards of

earth and disintegrated rock. We have, then, an aggregate of

750,000,000,000 cubic yards of such material, which, allowing to the

mountain surface in question an area of 50,000,000,000 square yards,

would cover the whole to the depth of fifteen yards. [Footnote: The total

superficies of the basin of the Po, down to Ponte Lagoscuro [Ferrara]--a

point where it has received all its affluents--is 6,938,200 hectares,

that is, 4,105,600 in mountain lands, 2,832,600 in plain lands.--Dumont,

Travaux Publics, etc., p. 272. These latter two quantities are equal

respectively to 10,145,348, and 6,999,638 acres, or 15,852 and 10,937

square miles.] There are very large portions of this area, where, as we

know from ancient remains--roads, bridges, and the like--from other

direct testimony, and from geological considerations, very little

degradation has taken place within twenty centuries, and hence the

quantity to be assigned to localities where the destructive causes have

been most active is increased in proportion.

If this vast mass of pulverized rock and earth were restored to the

localities from which it was derived, it certainly would not obliterate

valleys and gorges hollowed out by great geological causes, but it would

reduce the length and diminish the depth of ravines of later formation,

modify the inclination of their walls, reclothe with earth many bare

mountain ridges, essentially change the line of junction between plain

and mountain, and carry back a long reach of the Adriatic coast many

miles to the west. [Footnote: I do not use these quantities as factors

the value of which is precisely ascertained; nor, for the purposes of

the present argument, is quantitative exactness important. I employ

numerical statements simply as a means of aiding the imagination to form

a general and certainly not extravagant idea of the extent of

geographical revolutions which man has done much to accelerate, if not,

strictly speaking, to produce.

There is an old proverb, Dolus latet in generalibus, and Arthur Young in

not the only public economist who has warned his readers against the

deceitfulness of round numbers. I think, on the contrary, that vastly

more error has been produced by the affectation of precision in cases

where precision is impossible.

In all the great operations of terrestrial nature, the elements are so

numerous and so difficult of exact appreciation, that, until the means

of scientific observation and measurement are much more perfected than

they now are, we must content ourselves with general approximations. I

say TERRESTRIAL nature, because in cosmical movements we have fewer

elements to deal with, and may therefore arrive at much more rigorous

proportional accuracy in determination of time and place than we can in

fixing and predicting the quantities and the epochs of variable natural

phenomena on the earth's surface.

Travellers are often misled by local habits in the use of what may be

called representative numbers, where a definite is put for an indefinite

quantity. A Greek, who wished to express the notion of a great but

undetermined number, "myriad, or ten thousand;" a Roman, "six hundred;"

an Oriental, "forty," or, at present, very commonly, "fifteen thousand."

Many a tourist has gravely repeated, as an ascertained fact; the vague

statement of the Arabs and the monks of Mount Sinai, that the ascent

from the convent of St. Catherine to the summit of Gebel Moosa counts

"fifteen thousand" steps, though the difference of level is two thousand

feet; and the "Forty" Thieves, the "forty" martyr-monks of the convent

of El Arbain--not to speak of a similar use of this numeral in more

important cases--have often been understood as expressions of a known

number, when in fact they mean simply MANY. The number "fifteen

thousand" has found its way to Rome, and De Quincey seriously informs

us, on the authority of a lady who had been at much pains to ascertain

the EXACT truth, that, including closets large enough for a bed, the

Vatican contains fifteen thousand rooms. Any one who has observed the

vast dimensions of most of the apartments of that structure will admit

that we make a very small allowance of space when we assign a square

rod, sixteen and a half feet square, to each room upon the average. On

an acre, there might be one hundred and sixty such rooms, including

partition walls; and, to contain fifteen thousand of them, a building

must cover more than nine acres, and be ten stories high, or possess

other equivalent dimensions, which, as every traveller knows, many times

exceeds the truth.

The value of a high standard of accuracy in scientific observation can

hardly be overrated; but habits of rigorous exactness will never be

formed by an investigator who allows himself to trust implicitly to the

numerical precision or the results of a few experiments. The wonderful

accuracy of geodetic measurements in modern times is, in general,

attained by taking the mean of a great number of observations at every

station, and this final precision is but the mutual balance and

compensation of numerous errors.

The pretended exactness of statistical tables is too often little better

than an imposture; and those founded not on direct estimation by

competent observers, but on the report of persons who have no particular

interest in knowing the truth, but often have a motive for distorting

it, are commonly to be regarded as but vague guesses at the actual

fact.]

It is, indeed, not to be supposed that all the degradation of the

mountains is due to the destruction of the forests--that the flanks of

every Alpine valley in Central Europe below the snow-line were once

covered with earth and green with woods, but there are not many

particular cases in which we can, with certainty, or even with strong

probability, affirm the contrary.

Mountain Slides.

Terrible as are the ravages of the torrent and the river-flood, the

destruction of the woods exposes human life and industry to calamities

even more appalling than those which I have yet described. The slide in

the Notch of the White Mountains, by which the Willey family lost their

lives, is an instance of the sort I refer to, though I am not able to

say that in this particular case the slip of the earth and rock was

produced by the denudation of the surface. It may have been occasioned

by this cause, or by the construction of the road through the Notch, the

excavations for which, perhaps, cut through the natural buttresses that

supported the sloping strata above.

Not to speak of the fall of earth when the roots which held it together,

and the bed of leaves and mould which sheltered it both from

disintegrating frost and from sudden drenching and dissolution by heavy

showers, are gone, it is easy to see that, in a climate with severe

winters, the removal of the forest, and, consequently, of the soil it

had contributed to form, might cause the displacement and descent of

great masses of rock. The woods, the vegetable mould, and the soil

beneath, protect the rocks they cover from the direct action of heat and

cold, and from the expansion and contraction which accompany them. Most

rocks, while covered with earth, contain a considerable quantity of

water. [Footnote: Rock is permeable by water to a greater extent than is

generally supposed. Freshly quarried marble, and even granite, as well

as most other stones, are sensibly heavier, as well as softer and more

easily wrought, than after they are dried and hardened by air-seasoning.

Many sandstones are porous enough to serve as filters for liquids, and

much of that of Upper Egypt and Nubia hisses audibly when thrown into

water, from the escape of the air forced out of it by hydrostatic

pressure and the capillary attraction of the pores for water. Even the

denser silicious stones are penetrable by fluids and the coloring matter

they contain, to such an extent that agates and other forms of silex may

be artificially stained through their substance. The colors of the

stones cut at Oberstein are generally produced, or at least heightened,

by art. This art was known to and practised by the ancient lapidaries,

and it has been revived in recent times.]

A fragment of rock pervaded with moisture cracks and splits, if thrown

into a furnace, and sometimes with a loud detonation; and it is a

familiar observation that the fire, in burning over newly cleared lands,

breaks up and sometimes almost pulverizes the stones. This effect is due

partly to the unequal expansion of the stone, partly to the action of

heat on the water it contains in its pores. The sun, suddenly let in

upon rock which had been covered with moist earth for centuries,

produces more or less disintegration in the same way, and the stone is

also exposed to chemical influences from which it was sheltered before.

But in the climate of the United States as well as of the Alps, frost is

a still more powerful agent in breaking up mountain masses. The soil

that protects the lime and sandstone, the slate and the granite from the

influence of the sun, also prevents the water which filters into their

crevices and between their strata from freezing in the hardest winters,

and the moisture descends, in a liquid form, until it escapes in

springs, or passes off by deep subterranean channels. But when the

ridges are laid bare, the water of the autumnal rains fills the minutest

pores and veins and fissures and lines of separation of the rocks, then

suddenly freezes, and bursts asunder huge, and apparently solid blocks

of adamantine stone. [Footnote: Palissy had observed the action of frost

in disintegrating rock, and he thus describes it, in his essay on the

formation of ice: "I know that the stones of the mountains of Ardennes

be harder than marble. Nevertheless, the people of that country do not

quarry the said stones in winter, for that they be subject to frost; and

many times the rocks have been seen to fall without being cut, by means

whereof many people have been killed, when the said rocks were thawing."

Palissy was ignorant of the expansion of water in freezing--in fact, he

supposed that the mechanical force exerted by freezing-water was due to

compression, not dilatation--and therefore he ascribes to thawing alone

effects resulting not less from congelation.

Various forces combine to produce the stone avalanches of the higher

Alps, the fall of which is one of the greatest dangers incurred by the

adventurous explorers of those regions--the direct action of the sun

upon the stone, the expansion of freezing-water, and the loosening of

masses of rock by the thawing of the ice which supported them or held

them together.]

Where the strata are inclined at a considerable angle, the freezing of a

thin film of water over a large interstratal area might occasion a slide

that should cover miles with its ruins; and similar results might be

produced by the simple hydrostatic pressure of a column of water,

admitted, by the removal of the covering of earth, to flow into a

crevice faster than it could escape through orifices below. Earth or

rather mountain slides, compared to which the catastrophe that buried

the Willey family in New Hampshire was but a pinch of dust, have often

occurred in the Swiss, Italian, and French Alps. The land-slip, which

overwhelmed, and covered to the depth of seventy feet, the town of Plurs

in the valley of the Maira, on the night of the 4th of September, 1618,

sparing not a soul of a population of 2,430 inhabitants, is one of the

most memorable of these catastrophes, and the fall of the Rossberg or

Rufiberg, which destroyed the little town of Goldan in Switzerland, and

450 of its people, on the 2d of September, 1806, is almost equally

celebrated. In 1771, according to Wessely, the mountain-peak Piz, near

Alleghe in the province of Belluno, slipped into the bed of the

Cordevole, a tributary of the Piave, destroying in its fall three

hamlets and sixty lives. The rubbish filled the valley for a distance of

nearly two miles, and, by damming up the waters of the Cordevole, formed

a lake about three miles long, and a hundred and fifty feet deep, which

still subsists, though reduced to half its original length by the

wearing down of its outlet. [Footnote: Wessely, Die Oesterreichischen

Alpenlander und ihre Forste, pp. 125, 126. Wessely records several other

more or less similar occurrences in the Austrian Alps. Some of them,

certainly, are not to be ascribed to the removal of the woods, but in

most cases they are clearly traceable to that cause. See Revue des Eaux

et Forets for 1860, pp. 182, 205.]

The important provincial town of Veleia, near Piacenza, where many

interesting antiquities have been discovered within a few years, was

buried by a vast land-slip, probably about the time of Probus, but no

historical record of the event has survived to us.

On the 14th of February, 1855, the hill of Belmonte, a little below the

parish of San Stefano, in Tuscany, slid into the valley of the Tiber,

which consequently flooded the village to the depth of fifty feet, and

was finally drained off by a tunnel. The mass of debris is stated to

have been about 3,500 feet long, 1,000 wide, and not less than 600

high. [Footnote: Bianchi, Appendix to the Italian translation of Mrs.

Somerville'S Physical Geography, p. xxxvi.]

Occurrences of this sort have been so numerous in the Alps and

Apennines, that almost every Italian mountain commune has its tradition,

its record, or its still visible traces of a great land-slip within its

own limits. The old chroniclers contain frequent notices of such

calamities, and Giovanni Villani even records the destruction of fifty

houses and the loss of many lives by a slide of what seems to have been

a spur of the hill of San Giorgio in the city of Florence, in the year

1284. [Footnote: Cronica di Giovani Villani, lib. vii., cap. 97. For

descriptions of other slides in Italy, see same author, lib. xi, cap.

26; Fanfani, Antologia Italiana, parte ii., p. 95; Giuliani, Linguaggio

vivente della Toscana, 1865, lettera 63.]

Such displacements of earth and rocky strata rise to the magnitude of

geological convulsions, but they are of so rare occurrence in countries

still covered by the primitive forest, so common where the mountains

have been stripped of their native covering, and, in many cases, so

easily explicable by the drenching of incohesive earth from rain, or the

free admission of water between the strata of rocks--both of which a

coating of vegetation would have prevented--that we are justified in

ascribing them for the most part to the same cause as that to which the

destructive effects of mountain torrents are chiefly due--the felling of

the woods. [Footnote: There is good reason for thinking that many of the

earth and rock slides in the Alps occurred at an earlier period than the

origin of the forest vegetation which, in later ages, covered the flanks

of those mountains. See Bericht uber die Untersuchung der

Schweizerischen Hochgebirgswaldungen, 1862, p. 61.

Where more recent slides have been again clothed with woods, the trees,

shrubs, and smaller plants which spontaneously grow upon them are

usually of different species from those observed upon soil displaced at

remote periods. This difference is so marked that the site of a slide

can often be recognized at a great distance by the general color of the

foliage of its vegetation.]

In nearly every case of this sort the circumstances of which are

known--except the rare instances attributable to earthquakes--the

immediate cause of the slip has been the imbibition of water in large

quantities by bare earth, or its introduction between or beneath solid

strata. If water insinuates itself between the strata, it creates a

sliding surface, or it may, by its expansion in freezing, separate beds

of rock, which had been nearly continuous before, widely enough to allow

the gravitation of the superincumbent mass to overcome the resistance

afforded by inequalities of face and by friction; if it finds its way

beneath hard earth or rock reposing on clay or other bedding of similar

properties, it converts the supporting layer into a semi-fluid mud,

which opposes no obstacle to the sliding of the strata above.

The upper part of the mountain which buried Goldau was composed of a

hard but brittle conglomerate, called nagelflue, resting on unctuous

clay, and inclining rapidly towards the village. Much earth remained

upon the rock, in irregular masses, but the woods had been felled, and

the water had free access to the surface, and to the crevices which sun

and frost had already produced in the rock, and, of course, to the slimy

stratum beneath. The whole summer of 1806 had been very wet, and an

almost incessant deluge of rain had fallen the day preceding the

catastrophe, as well as on that of its occurrence. All conditions, then,

were favorable to the sliding of the rock, and, in obedience to the laws

of gravitation, it precipitated itself into the valley as soon as its

adhesion to the earth beneath it was destroyed by the conversion of the

latter into a viscous paste. The mass that fell measured between two and

a half and three miles in length by one thousand feet in width, and its

average thickness is thought to have been about a hundred feet. The

highest portion of the mountain was more than three thousand feet above

the village, and the momentum acquired by the rocks and earth in their

descent carried huge blocks of stone far up the opposite slope of the

Rigi.

The Piz, which fell into the Cordevole, rested on a steeply inclined

stratum of limestone, with a thin layer of calcareous marl intervening,

which, by long exposure to frost and the infiltration of water, had lost

its original consistence, and become a loose and slippery mass instead

of a cohesive and tenacious bed.

Protection against Avalanches.

In Switzerland and other snowy and mountainous countries, forests render

a most important service by preventing the formation and fall of

destructive avalanches, and in many parts of the Alps exposed to this

catastrophe, the woods are protected, though too often ineffectually, by

law. No forest, indeed, could arrest a large avalanche once in full

motion, but the mechanical resistance afforded by the trees prevents

their formation, both by obstructing the wind, which gives to the dry

snow of the Staub-Lawine, or dust-avalanche, its first impulse, and by

checking the disposition of moist snow to gather itself into what is

called the Rutsch-Lawine, or sliding avalanche. Marchand states that,

the very first winter after the felling of the trees on the higher part

of a declivity between Sannen and Gsteig where the snow had never been

known to slide, an avalanche formed itself in the clearing, thundered

down the mountain, and overthrew and carried with it a hitherto

unviolated forest to the amount of nearly a million cubic feet of

timber. [Footnote: Entwaldung der Gebirge, p. 41.] Elisee Reclus informs

us in his remarkable work, La Terre, vol. i., p. 212, that a mountain,

which rises to the south of the Pyrenaean village Araguanet in the upper

valley of the Neste, having been partially stripped of its woods, a

formidable avalanche rushed down from a plateau above in 1846, and swept

off more than 15,000 pine-trees. The path once opened down the flanks of

the mountain, the evil is almost beyond remedy. The snow sometimes

carries off the earth from the face of the rock, or, if the soil is

left, fresh slides every winter destroy the young plantations, and the

restoration of the wood becomes impossible. The track widens with every

new avalanche. Dwellings and their occupants are buried in the snow, or

swept away by the rushing mass, or by the furious blasts it occasions

through the displacement of the air; roads and bridges are destroyed;

rivers blocked up, which swell till they overflow the valley above, and

then, bursting their snowy barrier, flood the fields below with all the

horrors of a winter inundation. [Footnote: The importance of the wood in

preventing avalanches is well illustrated by the fact that, where the

forest is wanting, the inhabitants of localities exposed to snow-slides

often supply the place of the trees by driving stakes through the snow

into the ground, and thus checking its propensity to slip. The woods

themselves are sometimes thus protected against avalanches originating

on slopes above them, and as a further security, small trees are cut

down along the upper line of the forest, and laid against the trunks of

larger trees, transversely to the path of the slide, to serve as a fence

or dam to the motion of an incipient avalanche, which may by this means

be arrested before it acquires a destructive velocity and force.

In the volume cited in the text, Reclus informs us that "the village and

the great thermal establishment of Bareges in the Pyrenees were

threatened yearly by avalanches which precipitated themselves from a

height of 1,200 metres and at an angle of 35 degrees; so that the

inhabitants had been obliged to leave large spaces between the different

quarters of the town for the free passage of the descending masses.

Attempts have been recently made to prevent those avalanches by means

similar to those employed by the Swiss mountaineers. They cut terraces

three or four yards in width across the mountain slopes and supported

these terraces by a row of iron piles. Wattled fences, with here and

there a wall of stone, shelter the young shoots of trees, which grow up

by degrees under the protection of these defences. Until natural trees

are ready to arrest the snows, these artificial supports take their

place and do their duty very well. The only avalanche which swept down

the slope in the year 1860, when these works were completed, did not

amount to 350 cubic yards, while the masses which fell before this work

was undertaken contained from 75,000 to 80,000 cubic yards."--La Terre,

vol. i., p. 233.]

Minor Uses of the Forest.

Besides the important conservative influences of the forest and its

value as the source of supply of a material indispensable to all the

arts and industries of human life, it renders other services of a less

obvious and less generally recognized character.

Woods often subserve a valuable purpose in preventing the fall of rocks,

by mere mechanical resistance. Trees, as well as herbaceous vegetation,

grow in the Alps upon declivities of surprising steepness of

inclination, and the traveller sees both luxuriant grass and flourishing

woods on slopes at which the soil, in the dry air of lower regions,

would crumble and fall by the weight of its own particles. When loose

rocks lie scattered on the face of these declivities, they are held in

place by the trunks of the trees, and it is very common to observe a

stone that weighs hundreds of pounds, perhaps even tons, resting against

a tree which has stopped its progress just as it was beginning to slide

down to a lower level. When a forest in such a position is cut, these

blocks lose their support, and a single wet season is enough not only to

bare the face of a considerable extent of rock, but to cover with earth

and stone many acres of fertile soil below. [Footnote: See in Kohl,

Alpenreisen, i., 120, an account of the ruin of fields and pastures, and

even of the destruction of a broad belt of forest, by the fall of rocks

in consequence of cutting a few large trees. Cattle are very often

killed in Switzerland by rock-avalanches, and their owners secure

themselves from loss by insurance against this risk as against damage by

fire or hail.]

In alluvial plains and on the banks of rivers trees are extremely useful

as a check to the swift flow of the water in inundations, and the spread

of the mineral material it transports; but this will be more

appropriately considered in the chapter on the Waters; and another most

important use of the woods, that of confining the loose sands of dunes

and plains, will be treated of in the chapter on the Sands.

Small Forest Plants, and Vitality of Seed.

Another function of the woods, to which I have barely alluded, deserves

a fuller notice than can be bestowed upon it in a treatise the scope of

which is purely economical. The forest is the native habitat of a large

number of humbler plants, to the growth and perpetuation of which its

shade, its humidity, and its vegetable mould appear to be indispensable

necessities. [Footnote: "A hundred and fifty paces from my house is a

hill of drift-sand, on which stood a few scattered pines (Pinus

sylvestris). Sempervivum tectorum in abundance, Statice armeria, Ammone

vernalis, Dianthus carthusianorum, with other sand-plants, were growing

there. I planted the hill with a few birches, and all the plants I have

mentioned completely disappeared, though there were many naked spots of

sand between the trees. It should be added, however, that the hillock is

more thickly wooded than before. . . . It seems then that Sempervivum

tectorum, etc., will not bear the neighborhood of the birch, though

growing well near the Pinus sylvestris. I have found the large red

variety of Agaricus deliciosus only among the roots of the pine; the

greenish-blue Agaricus deliciosus among alder roots, but not near any

other tree. Birds have their partialities among trees and shrubs. The

Silvioe prefer the Pinus Larix to other trees. In my garden this Pinus

is never without them, but I never saw a bird perch on Thuja

occidentalis or Juniperus sabina, although the thick foliage of these

latter trees affords birds a better shelter than the loose leafage of

other trees. Not even a wren ever finds its way to one of them. Perhaps

the scent of the Thuja and the Juniperus is offensive to them. I have

spoiled one of my meadows by cutting away the bushes. It formerly bore

grass four feet high, because many umbelliferous plants, such as

Heracleum spondylium, Spiraea ulmaria, Laserpitium latifolia, etc., grew

in it. Under the shelter of the bushes these plants ripened and bore

seed, but they gradually disappeared as the shrubs wore extirpated, and

the grass now does not grow to the height of more than two feet, because

it is no longer obliged to keep pace with the umbellifera which

flourished among it." See a paper by J.G. Buttner, of Kurland, in

Berghaus s Geographicsches Jahrbuch, 1852, No. 4, pp. 14, 15.

These facts are interesting as illustrating the multitude of often

obscure conditions upon which the life or vigorous growth of smaller

organisms depends. Particular species of truffles and of mushrooms are

found associated with particular trees, without being, as is popularly

supposed, parasites deriving their nutriment from the dying or dead

roots of those trees. The success of Rousseau's experiments seem

decisive on this point, for he obtains larger crops of truffles from

ground covered with young seedling oaks than from that filled with roots

of old trees. See an article on Mont Ventoux, by Charles Martins, in the

Revue des Deux Mondes, Avril, 1863, p. 626.

It ought to be much more generally known than it is, that most if not

all mushrooms, even of the species reputed poisonous, may be rendered

harmless and healthful as food by soaking them for two hours in

acidulated or salt water. The water requires two or three spoonfuls of

vinegar or two spoonful of gray salt to the quart, and a quart of water

is enough for a pound of sliced mushrooms. After thus soaking, they are

well washed in fresh water, thrown into cold water, which is raised to

the boiling-point, and, after remaining half an hour, taken out and

again washed, Gerard, to prove that "crumpets is wholesome," ate one

hundred and seventy-five pounds of the most poisonous mushrooms thus

prepared, in a single month, fed his family ad libitum with the same,

and finally administered them, in heroic doses, to the members of a

committee appointed by the Council of Health of the city of Paris. See

Figuier, L'Annee Scientifique, 1862, pp. 353, 384. It should be observed

that the venomous principle of poisonous mushrooms is not decomposed and

rendered innocent by the process described in the note. It is merely

extracted by the acidulated or saline water employed for soaking the

plants, and care should be taken that this water be thrown away out of

the reach of mischief.

It has long been known that the Russian peasantry eat, with impunity,

mushrooms of species everywhere else regarded as very poisonous. Is it

not probable that the secret of rendering them harmless--which was known

to Pliny, though since forgotten in Italy--is possessed by the rustic

Muscovites ]

We cannot positively say that the felling of the woods in a given

vegetable province would involve the final extinction of the smaller

plants which are found only within their precincts. Some of these,

though not naturally propagating themselves in the open ground, may

perhaps germinate and grow under artificial stimulation and protection,

and finally become hardy enough to maintain an independent existence in

very different circumstances from those which at present seem essential

to their life.

Besides this, although the accounts of the growth of seeds, which have

lain for ages in the ashy dryness of Egyptian catacombs, are to be

received with great caution, or, more probably, to be rejected

altogether, yet their vitality seems almost imperishable while they

remain in the situations in which nature deposits them. When a forest

old enough to have witnessed the mysteries of the Druids is felled,

trees of other species spring up in its place; and when they, in their

turn, fall before the axe, sometimes even as soon as they have spread

their protecting shade over the surface, the germs which their

predecessors had shed years, perhaps centuries before, sprout up, and in

due time, if not choked by other trees belonging to a later stage in the

order of natural succession, restore again the original wood. In these

cases, the seeds of the new crop may have been brought by the wind, by

birds, by quadrupeds, or by other causes; but, in many instances, this

explanation is not probable.

When newly cleared ground is burnt over in the United States, the ashes

are hardly cold before they are covered with a crop of fire-weed,

Senecio hieracifolius, a tall, herbaceous plant, very seldom seen

growing under other circumstances, and often not to be found for a

distance of many miles from the clearing. Its seeds, whether the fruit

of an ancient vegetation or newly sown by winds or birds, require either

a quickening by a heat which raises to a certain high point the

temperature of the stratum where they lie buried, or a special pabulum

furnished only by the combustion of the vegetable remains that cover the

ground in the woods.

Earth brought up from wells or other excavations soon produces a harvest

of plants often very unlike those of the local flora, and Hayden informs

us that on our great Western desert plains, "wherever the earth is

broken up, the wild sun-flower (Helianthus) and others of the

taller-growing plants, though previously unknown in the vicinity, at

once spring up, almost as if spontaneous generation had taken place."

[Footnote: Geological Survey of Wyoming, p. 455.]

Moritz Wagner, as quoted by Wittwer, [Footnote: Physikalische

Geographie, p. 486.] remarks in his description of Mount Ararat: "A

singular phenomenon to which my guide drew my attention is the

appearance of several plants on the earth-heaps left by the last

catastrophe [an earthquake], which grow nowhere else on the mountain,

and had never been observed in this region before. The seeds of these

plants were probably brought by birds, and found in the loose, clayey

soil remaining from the streams of mud, the conditions of growth which

the other soil of the mountain refused them." This is probable enough,

but it is hardly less so that the flowing mud brought them up to the

influence of air and sun, from depths where a previous convulsion had

buried them ages before.

Seeds of small sylvan plants, too deeply buried by successive layers of

forest foliage and the mould resulting from its decomposition to be

reached by the plough when the trees are gone and the ground brought

under cultivation, may, if a wiser posterity replants the wood which

sheltered their parent stems, germinate and grow, after lying for

generations in a state of suspended animation.

Darwin says: "On the estate of a relation there was a large and

extremely barren heath, which had never been touched by the hand of man,

but several hundred acres of exactly the same nature had been enclosed

twenty-five years previously and planted with Scotch fir. The change in

the native vegetation of the planted part of the heath was most

remarkable--more than is generally seen in passing from one quite

different soil to another; not only the proportional numbers of the

heath-plants were wholly changed, but TWELVE SPECIES of plants (not

counting grasses and sedges) flourished in the plantation which could

not be found on the heath." [Footnote: Origin of Species, American

edition, p. 60.] Had the author informed us that these twelve plants

belonged to species whose seeds enter into the nutriment of the birds

which appeared with the young wood, we could easily account for their

presence in the soil; but he says distinctly that the birds were of

insectivorous species, and it therefore seems more probable that the

seeds had been deposited when an ancient forest protected the growth of

the plants which bore them, and that they sprang up to new life when a

return of favorable conditions awaked them from a sleep of centuries.

Darwin indeed says that the heath "had never been touched by the hand of

man." Perhaps not, after it became a heath; but what evidence is there

to control the general presumption that this heath was preceded by a

forest, in whose shade the vegetables which dropped the seeds in

question might have grown [Footnote: Writers on vegetable physiology

record numerous instances where seeds have grown after lying dormant for

ages. The following cases are mentioned by Dr. Dwight (Travels, ii., pp.

438, 430).

"The lands [in Panton, Vermont], which have here been once cultivated,

and again permitted to lie waste for several years, yield a rich and

fine growth of hickory [Carya Porcina]. Of this wood there is not, I

believe, a single tree in any original forest within fifty miles from

this spot. The native growth was here white pine, of which I did not see

a single stem in a whole grove of hickory."

The hickory is a walnut, bearing a fruit too heavy to be likely to be

carried fifty miles by birds, and besides, I believe it is not eaten by

any bird indigenous to Vermont. We have seen, however, on a former page,

that birds transport the nutmeg, which when fresh is probably as heavy

as the walnut, from one inland of the Indian archipelago to another.