This supposed increase in the frequency and quantity of rain in Lower

Egypt is, I think, an error, or at least not an established fact. I have

heard it disputed on the spot by intelligent Franks, whose residence in

that country began before the plantations of Mehemet Ali and Ibrahim

Pacha, and I have been assured by them that meterological observations,

made at Alexandria about the begiuning of this century, show an annual

fall of rain as great as is usual at this day. The mere fact that it did

not rain during the French occupation is not conclusive. Having

experienced a gentle shower of nearly twenty-four hours' duration in

Upper Egypt, I inquired of the local governor in relation to the

frequency of this phenomenon, and was told by him that not of drop of

rain had fallen at that point for more than two years previous.

The belief in the increase of rain in Egypt rests almost entirely on the

observations of Marshal Marmont, and the evidence collected by him in

1836. His conclusions have been disputed, if not confuted, by Joinard

and others, and are probably erroneous. See Foissac, Meteorologie,

German translation, pp. 634-639.

It certainly sometimes rains briskly at Cairo, but evaporation is

exceedingly rapid in Egypt--as any one who ever saw a Fellah woman wash

a napkin in the Nile, and dry it by shaking it a few moments in the air,

can testify; and a heap of grain, wet a few inches below the surface,

would probably dry again without injury. At any rate, the Egyptian

Government often has vast quantities of wheat stored at Boulak in

uncovered yards through the winter, though it must be admitted that the

slovenliness and want of foresight in Oriental life, public and private,

are such that we cannot infer the safety of any practice followed in the

East merely from its long continuance.

Grain, however, may be long kept in the open air in climates much less

dry than that of Egypt, without injury, except to the superficial

layers; for moisture does not penetrate to a great depth in a heap of

grain once well dried and kept well aired. When Louis IX. was making his

preparations for his campaign in the East, he had large quantities of

wine and grain purchased in the Island of Cyprus, and stored up for two

years to await his arrival. "When we were come to Cyprus," says

Joinville, Histoire de Saint Louis, Section 72, 73, "we found there

greate foison of the Kynge's purveyance. . . The wheate and the barley

they had piled up in greate heapes in the feeldes, and to looke vpon,

they were like vnto mountaynes; for the raine, the whyche hadde beaten

vpon the wheate now a longe whyle, had made it to sproute on the toppe,

so that it seemed as greene grasse. And whanne they were mynded to

carrie it to Egypte, they brake that sod of greene herbe, and dyd finde

under the same the wheate and the barley, as freshe as yf menne hadde

but nowe thrashed it."]

Total Climatic Influence of the Forest.

Aside from the question of local disturbances and their compensations,

it does not seem probable that the forests sensibly affect the general

mean of atmospheric temperature of the globe, or the total quantity of

precipitation, or even that they had this influence when their extent

was vastly greater than at present. The waters cover about three-fourths

of the face of the earth, and if we deduct the frozen zones, the peaks

and crests of lofty mountains and their craggy slopes, the Sahara and

other great African and Asiatic deserts, and all such other portions of

the solid surface as are permanently unfit for the growth of wood, we

shall find that probably not one-tenth of the total superficies of our

planet was ever, at any one time in the present geological period,

covered with forests. Besides this, the distribution of forest land, of

desert, and of water, is such as to reduce the possible influence of the

woods to a low expression; for the forests are, in large proportion,

situated in cold or temperate climates, where the action of the sun is

comparatively feeble both in elevating temperature and in promoting

evaporation; while, in the torrid zone, the desert and the sea--the

latter of which always presents an evaporable surface--enormously

preponderate. It is, upon the whole, not probable that so small an

extent of forest, so situated, could produce a sensible influence on the

general climate of the globe, though it might appreciably affect the

local action of all climatic elements. The total annual amount of solar

heat absorbed and radiated by the earth, and the sum of terrestrial

evaporation and atmospheric precipitation, must be supposed constant;

but the distribution of heat and of humidity is exposed to disturbance

in both time and place by a multitude of local causes, among which the

presence or absence of the forest is doubtless one.

So far as we are able to sum up the results, it would appear that, in

countries in the temperate zone still chiefly covered with wood, the

summers would be cooler, moister, shorter, the winters milder, drier,

longer, than in the same regions after the removal of the forest, and

that the condensation and precipitation of atmospheric moisture would

be, if not greater in total quantity, more frequent and less violent in

discharge. The slender historical evidence we possess seems to point to

the same conclusion, though there is some conflict of testimony and of

opinion on this point.

Among the many causes which, as we have seen, tend to influence the

general result, the mechanical action of the forest, if not more

important, is certainly more obvious and direct than the immediate

effects of its organic processes. The felling of the woods involves the

sacrifice of a valuable protection against the violence of chilling

winds and the loss of the shelter afforded to the ground by the thick

coating of leaves which the forest sheds upon it and by the snow which

the woods prevent from blowing away, or from melting in the brief thaws

of winter. I have already remarked that bare ground freezes much deeper

than that which is covered by beds of leaves, and when the earth is

thickly coated with snow, the strata frozen before it fell begin to

thaw. It is not uncommon to find the ground in the woods, where the snow

lies two or three feet deep, entirely free from frost, when the

atmospheric temperature has been for several weeks below the

freezing-point, and for some days even below the zero of Fahrenheit.

When the ground is cleared and brought under cultivation, the leaves are

ploughed into the soil and decomposed, and the snow, especially upon

knolls and eminences, is blown off, or perhaps half thawed, several

times during the winter. The water from the melting snow runs into the

depressions, and when, after a day or two of warm sunshine or tepid

rain, the cold returns, it is consolidated to ice, and the bared ridges

and swells of earth are deeply frozen. [Footnote: I have seen, in

Northern New England, the surface of the open ground frozen to the depth

of twenty-two inches, in the month of November, when in the forest-earth

no frost was discoverable; and later in the winter, I have known an

exposed sand-knoll to remain frozen six feet deep, after the ground in

the woods was completely thawed.] It requires many days of mild weather

to raise the temperature of soil in this condition, and of the air in

contact with it, to that of the earth in the forests of the same

climatic region. Flora is already plaiting her sylvan wreath before the

corn-flowers which are to deck the garland of Ceres have waked from

their winter's sleep; and it is probably not a popular error to believe

that, where man has substituted his artificial crops for the spontaneous

harvest of nature, spring delays her coming. [Footnote: The conclusion

arrived at by Noah Webster, in his very learned and able paper on the

supposed change in the temperature of winter, read before the

Connecticut Academy of Arts and Sciences in 1799, was as follows: "From

a careful comparison of these facts, it appears that the weather, in

modern winters, in the United States, is more inconstant than when the

earth was covered with woods, at the first settlement of Europeans in

the country; that the warm weather of autumn extends further into the

winter months, and the cold weather of winter and spring encroaches upon

the summer; that, the wind being more variable, snow is less permanent,

and perhaps the same remark may be applicable to the ice of the rivers.

These effects seem to result necessarily from the greater quantity of

heat accumulated in the earth in summer since the ground has been

cleared of wood and exposed to the rays of the sun, and to the greater

depth of frost in the earth in winter by the exposure of its uncovered

surface to the cold atmosphere."--Collection of Papers by Noah Webster,

p. 162.]

There are, in the constitution and action of the forest, many forces,

organic and inorganic, which unquestionably tend powerfully to produce

meteorological effects, and it may, therefore, be assumed as certain

that they must and do produce such effects, UNLESS they compensate and

balance each other, and herein lies the difficulty of solving the

question. To some of these elements late observations give a new

importance. For example, the exhalation of aqueous vapor by plants is

now believed to be much greater, and the absorption of aqueous vapor by

them much less, than was formerly supposed, and Tyndall's views on the

relations of vapor to atmospheric heat give immense value to this factor

in the problem. In like manner the low temperature of the surface of

snow and the comparatively high temperature of its lower strata, and its

consequent action on the soil beneath, and the great condensation of

moisture by snow, are facts which seem to show that the forest, by

protecting great surfaces of snow from melting, must inevitably exercise

a great climatic influence. If to these influences we add the mechanical

action of the woods in obstructing currents of wind, and diminishing the

evaporation and refrigeration which such currents produce, we have an

accumulation of forces which MUST manifest great climatic effects,

unless--which is not proved and cannot be presumed--they neutralize each

other. These are points hitherto little considered in the discussion,

and it seems difficult to deny that as a question of ARGUMENT, the

probabilities are strongly in favor of the meteorological influence of

the woods. The EVIDENCE, indeed, is not satisfactory, or, to speak more

accurately, it is non-existent, for there really is next to no

trustworthy proof on the subject, but it appears to me a case where the

burden of proof must be taken by those who maintain that, as a

meteorological agent, the forest is inert.

The question of a change in the climate of the Northern American States

is examined in the able Meteorological Report of Mr. Draper, Director of

the New York Central Park Observatory, for 1871. The result arrived at

by Mr. Draper is, that there is no satisfactory evidence of a diminution

in the rainfall, or of any other climatic change in the winter season,

in consequence of clearing of the forests or other human action. The

proof from meteorological registers is certainly insufficient to

establish the fact of a change of climate, but, on the other hand, it is

equally insufficient to establish the contrary. Meteorological stations

are too few, their observations, in many cases, extend over a very short

period, and, for reasons I have already given, the great majority of

their records are entitled to little or no confidence. [Footnote: Since

these pages were written, the subject of forest meteorology has received

the most important contribution ever made to it, in several series of

observations at numerous stations in Bavaria, from the year 1866 to

1871, published by Ebermayer, at Aschaffenburg, in 1873, under the

title: Die Physikalischen Einwirkungen des Waldes auf Luft und Boden,

und seine Klimatologische und Hygienische Bedeutung. I. Band. So far as

observations of only five years' duration can prove anything, the

following propositions, not to speak of many collateral and subsidiary

conclusions, seem to be established, at least for the localities where

the observations were made:

1. The yearly mean temperature of wooded soils, at all depths, is lower

than that of open grounds, p. 85.

This conclusion, it may be remarked, is of doubtful applicability in

regions of excessive climate like the Northern United States and Canada,

where the snow keeps the temperature of the soil in the forest above the

freezing-point, for a large part and sometimes the whole of the winter,

while in unwooded ground the earth remains deeply frozen.

2. The yearly mean atmospheric temperature, other things being equal, is

lower in the forest than in cleared grounds, p. 84.

3. Climates become excessive in consequence of extensive clearings, p.

117.

4. The ABSOLUTE humidity of the air in the forest is about the same as

in open ground, while the RELATIVE humidity is greater in the former

than in the latter case, on account of the lower temperature of the

atmosphere in the wood, p. 150.

5. The evaporation from an exposed surface of water in the forest is

sixty-four per cent. less than in unwooded grounds, pp. 159,161.

6. About twenty-six per cent. of the precipitation is interrupted and

prevented from reaching the ground by the foliage and branches of forest

trees, p. 194.

7. In the interior of thick woods, the evaporation from water and from

earth is much less than the precipitation, p. 210.

8. The loss of the water of precipitation intercepted by the trees in

the forest is compensated by the smaller evaporation from the ground, p.

219.

9. In elevated regions and during the summer half of the year, woods

tend to increase the precipitation, p. 202.]

Influence of the Forest on the Humidity of the Soil.

I have hitherto confined myself to the influence of the forest on

meteorological conditions, a subject, as has been seen, full of

difficulty and uncertainty. Its comparative effects on the temperature,

the humidity, the texture and consistence, the configuration and

distribution of the mould or arable soil, and, very often, of the

mineral strata below, and on the permanence and regularity of springs

and greater superficial water-courses, are much less disputable as well

as more easily estimated and more important, than its possible value as

a cause of strictly climatic equilibrium or disturbance.

The action of the forest on the earth is chiefly mechanical, but the

organic process of absorption of moisture by its roots affects the

quantity of water contained in the vegetable mould and in the mineral

strata near the surface, and, consequently, the consistency of the soil.

In treating of the effects of trees on the moisture of the atmosphere, I

have said that the forest, by interposing a canopy between the sky and

the ground, and by covering the surface with a thick mantle of fallen

leaves, at once obstructed insulation and prevented the radiation of

heat from the earth. These influences go far to balance each other; but

familiar observation shows that, in summer, the forest-soil is not

raised to so high a temperature as open grounds exposed to irradiation.

For this reason, and in consequence of the mechanical resistance opposed

by the bed of dead leaves to the escape of moisture, we should expect

that, except after recent rains, the superficial strata of woodland-soil

would be more humid than that of cleared land. This agrees with

experience. The soil of the natural forest is always moist, except in

the extremest droughts, and it is exceedingly rare that a primitive wood

suffers from want of humidity. How far this accumulation of water

affects the condition of neighboring grounds by lateral infiltration, we

do not know, but we shall see, in a subsequent chapter, that water is

conveyed to great distances by this process, and we may hence infer that

the influence in question is an important one.

It is undoubtedly true that loose soils, stripped of vegetation and

broken up by the plough or other processes of cultivation, may, until

again carpeted by grasses or other plants, absorb more rain and

snow-water than when they were covered by a natural growth; but it is

also true that the evaporation from such soils is augmented in a still

greater proportion. Rain scarcely penetrates beneath the sod of

grass-ground, but runs off over the surface; and after the heaviest

showers a ploughed field will often be dried by evaporation before the

water can be carried off by infiltration, while the soil of a

neighboring grove will remain half saturated for weeks together. Sandy

soils frequently rest on a tenacious subsoil, at a moderate depth, as is

usually seen in the pine plains of the United States, where pools of

rain-water collect in slight depressions on the surface of earth the

upper stratum of which is as porous as a sponge. In the open grounds

such pools are very soon dried up by the sun and wind; in the woods they

remain unevaporated long enough for the water to diffuse itself

laterally until it finds, in the subsoil, crevices through which it may

escape, or slopes which it may follow to their outcrop or descend along

them to lower strata.

Drainage by Roots of Trees.

Becquerel notices a special function of the forest to which I have

already alluded, but to which sufficient importance has not, until very

recently, been generally ascribed. I refer to the mechanical action of

the roots as conductors of the superfluous humidity of the superficial

earth to lower strata. The roots of trees often penetrate through

subsoil almost impervious to water, and in such cases the moisture,

which would otherwise remain above the subsoil and convert the

surface-earth into a bog, follows the roots downwards and escapes into

more porous strata or is received by subterranean canals or reservoirs.

[Footnote: "The roots of vegetables," says d'Hericourt, "perform the

office of draining in a manner analogous to that artificially practised

in parts of Holland and the British islands. This method consists in

driving deeply down into the soil several hundred stakes to the acre;

the water filters down along the stakes, and in some cases as favorable

results have been obtained by this means as by horizontal

drains."-Annales Forestieres, 1837, p. 312.] When the forest is felled,

the roots perish and decay, the orifices opened by them are soon

obstructed, and the water, after having saturated the vegetable earth,

stagnates on the surface and transforms it into ponds and morasses. Thus

in La Brenne, a tract of 200,000 acres resting on an impermeable subsoil

of argillaceous earth, which ten centuries ago was covered with forests

interspersed with fertile and salubrious meadows and pastures, has been

converted, by the destruction of the woods, into a vast expanse of

pestilential pools and marshes. In Sologne the same cause has withdrawn

from cultivation and human inhabitation not less than 1,100,000 acres of

ground once well wooded, well drained, and productive.

It is an important observation that the desiccating action of trees, by

way of drainage or external conduction by the roots, is greater in the

artificial than in the natural wood, and hence that the surface of the

ground in the former is not characterized by that approach to a state of

saturation which it so generally manifests in the latter. In the

spontaneous wood, the leaves, fruits, bark, branches, and dead trunks,

by their decayed material and by the conversion of rock into loose earth

through the solvent power of the gases they develop in decomposition,

cover the ground with an easily penetrable stratum of mixed vegetable

and mineral matter extremely favorable to the growth of trees, and at

the same time too retentive of moisture to part with it readily to the

capillary attraction of the roots.

The trees, finding abundant nutriment near the surface, and so sheltered

against the action of the wind by each other as not to need the support

of deep and firmly fixed stays, send their roots but a moderate distance

downwards, and indeed often spread them out like a horizontal network

almost on the surface of the ground. In the artificial wood, on the

contrary, the spaces between the trees are greater; they are obliged to

send their roots deeper both for mechanical support and in search of

nutriment, and they consequently serve much more effectually as conduits

for perpendicular drainage.

It is only under special circumstances, however, that this function of

the forest is so essential a conservative agent as in the two cases just

cited. In a champaign region insufficiently provided with natural

channels for the discharge of the waters, and with a subsoil which,

though penetrable by the roots of trees, is otherwise impervious to

water, it is of cardinal importance; but though trees everywhere tend to

carry off the moisture of the superficial strata by this mode of

conduction, yet the precise condition of soil which I have described is

not of sufficiently frequent occurrence to have drawn much attention to

this office of the wood. In fact, in most soils, there are counteracting

influences which neutralize, more or less effectually, the desiccative

action of roots, and in general it is as true as it was in Seneca's

time, that "the shadiest grounds are the moistest." [Footnote: Seneca,

Questiones Naturales, iii. 11, 2.]

It is always observed in the American States, that clearing the ground

not only causes running springs to disappear, but dries up the stagnant

pools and the spongy soils of the low grounds. The first roads in those

States ran along the ridges, when practicable, because there only was

the earth dry enough to allow of their construction, and, for the same

reason, the cabins of the first settlers were perched upon the hills. As

the forests have been from time to time removed, and the face of the

earth laid open to the air and sun, the moisture has been evaporated,

and the removal of the highways and of human habitations from the bleak

hills to the sheltered valleys, is one of the most agreeable among the

many improvements which later generations have witnessed in the interior

of the Northern States. [Footnote: The Tuscan poet Ginati, who hod

certainly had little opportunity of observing primitive conditions of

nature and of man, was aware that such must have been the course of

things in new countries. "You know," says he in a letter to a friend,

"that the hills were first occupied by man, because stagnant waters, and

afterwards continual wars, excluded men from the plains. But when

tranquillity was established and means provided for the discharge of the

waters, the low grounds were soon covered with human habitations."--

Letters, Firenze, 1864, p. 98.]

Recent observers in France affirm that evergreen trees exercise a

special desiccating action on the soil, and cases are cited where large

tracts of land lately planted with pines have been almost completely

drained of moisture by some unknown action of the trees. It is argued

that the alleged drainage is not due to the conducting power of the

roots, inasmuch as the roots of the pine do not descend lower than those

of the oak and other deciduous trees which produce no such effect, and

it is suggested that the foliage of the pine continues to exhale through

the winter a sufficient quantity of moisture to account for the drying

up of the soil. This explanation is improbable, and I know nothing in

American experience of the forest which accords with the alleged facts.

It is true that the pines, the firs, the hemlock, and all the

spike-leaved evergreens prefer a dry soil, but it has not been observed

that such soils become less dry after the felling of their trees. The

cedars and other trees of allied families grow naturally in moist

ground, and the white cedar of the Northern States, Thuya occidentalis,

is chiefly found in swamps. The roots of this tree do not penetrate

deeply into the earth, but are spread out near the surface, and of

course do not carry off the waters of the swamp by perpendicular

conduction. On the contrary, by their shade, the trees prevent the

evaporation of the superficial water; but when the cedars are felled,

the swamp--which sometimes rather resembles a pool filled with aquatic

trees than a grove upon solid ground--often dries up so completely as to

be fit for cultivation without any other artificial drainage than, in

the ordinary course of cultivation, is given to other new soils.

[Footnote: A special dessicative influence has long been ascribed to the

maritime pine, which has been extensively planted on the dunes and

sand-plains of western France, and it is well established that, under

certain conditions, all trees, whether evergreen or deciduous, exercise

this function, but there is no convincing proof that in the cases now

referred to there is any difference in the mode of action of the two

classes of trees. An article by D'Arbois de Jubainville in the Revue des

Eaux et Forets for April, 1869, ascribing the same action to the Pinus

sylvestris, has excited much attention in Europe, and the facts stated

by this writer constitute the strongest evidence known to me in support

of the alleged influence of evergreen trees, as distinguished from the

draining by downward conduction, which is a function exercised by all

trees, under ordinary circumstances, in proportion to their penetration

of a bibulous subsoil by tap or other descending roots. The question has

been ably discussed by Beraud in the Revue des Deux Mondes for April,

1870, the result being that the drying of the soil by pines is due

simply to conduction by the roots, whatever may be the foliage of the

tree. See post: Influence of the Forest on Flow of Springs. It is

however certain, I believe, that evergreens exhale more moisture in

winter than leafless deciduous trees, and consequently some weight is to

be ascribed to this element.]

The Forest in Winter.

The influence of the woods on the flow of springs, and consequently on

the supply for the larger water-courses, naturally connects itself with

the general question of the action of the forest on the humidity of the

ground. But the special condition of the woodlands, as affected by snow

and frost in the winter of excessive climates, like that of the United

States, has not been so much studied as it deserves; and as it has a

most important bearing on the superficial hydrology of the earth, I

shall make some observations upon it before I proceed to the direct

discussion of the influence of the forest on the flow of springs.

To estimate rightly the importance of the forest in our climate as a

natural apparatus for accumulating the water that falls upon the surface

and transmitting it to the subjacent strata, we must compare the

condition and properties of its soil with those of cleared and

cultivated earth, and examine the consequently different action of these

soils at different seasons of the year. The disparity between them is

greatest in climates where, as in the Northern American States and in

the extreme North of Europe, the open ground freezes and remains

impervious to water during a considerable part of the winter; though,

even in climates where the earth does not freeze at all, the woods have

still an important influence of the same character. The difference is

yet greater in countries which have regular wet and dry seasons, rain

being very frequent in the former period, while, in the latter, it

scarcely occurs at all. These countries lie chiefly in or near the

tropics, but they are not wanting in higher latitudes; for a large part

of Asiatic and even of European Turkey is almost wholly deprived of

summer rains. In the principal regions occupied by European cultivation,

and where alone the questions discussed in this volume are recognized as

having, at present, any practical importance, more or less rain falls at

all seasons, and it is to these regions that, on this point as well as

others, I chiefly confine my attention.

Importance of Snow.

Recent observations in Switzerland give a new importance to the

hygrometrical functions of snow, and of course to the forest as its

accumulator and protector. I refer to statements of the condensation of

atmospheric vapor by the snows and glaciers of the Rhone basin, where it

is estimated to be nearly equal to the entire precipitation of the

valley. Whenever the humidity of the atmosphere in contact with snow is

above the point of saturation at the temperature to which the air is

cooled by such contact, the superfluous moisture is absorbed by the snow

or condensed and frozen upon its surface, and of course adds so much to

the winter supply of water received from the snow by the ground. This

quantity, in all probability, much exceeds the loss by evaporation, for

during the period when the ground is covered with snow, the proportion

of clear dry weather favorable to evaporation is less than that of humid

days with an atmosphere in a condition to yield up its moisture to any

bibulous substance cold enough to condense it. [Footnote: The hard

snow-crust, which in the early spring is a source of such keen enjoyment

to the children and youth of the North--and to many older persons in

whom the love of nature has kept awake a relish for the simple pleasures

of rural life--is doubtless due to the congelation of the vapor

condensed by the snow rather than to the thawing and freezing of the

superficial stratum; for when the surface is melted by the sun, the

water is taken up by the absorbent mass beneath before the temperature

falls low enough to freeze it.]

In our Northern States, irregular as is the climate, the first autumnal

snows pretty constantly fall before the ground is frozen at all, or when

the frost extends at most to the depth of only a few inches. [Footnote:

The hard autumnal frosts are usually preceded by heavy rains which

thoroughly moisten the soil, and it is a common saying in the North that

"the ground will not freeze till the swamps are full."] In the woods,

especially those situated upon the elevated ridges which supply the

natural irrigation of the soil and feed the perennial fountains and

streams, the ground remains covered with snow during the winter; for the

trees protect the snow from blowing from the general surface into the

depressions, and new accessions are received before the covering

deposited by the first fall is melted. Snow is of a color unfavorable

for radiation, but, even when it is of considerable thickness, it is not

wholly impervious to the rays of the sun, and for this reason, as well

as from the warmth of lower strata, the frozen crust of the soil, if one

has been formed, is soon thawed, and does not again fall below the

freezing-point during the winter. [Footnote: Dr. Williams, of Vermont,

made some observations on the comparative temperature of the soil in

open and in wooded ground In the years 1789 and 1791, but they generally

belonged to the warmer months, and I do not know that any extensive

series of comparisons between the temperature of the ground in the woods

and in the fields has been attempted in America. Dr. Williams's

thermometer was sunk to the depth of ten inches, and gave the following

results:

----

| Temperature | Temperature |

Time. | of ground in| of ground in| Difference.

| pasture. | woods. |

----

May 23......................| 52 | 46 | 6

" 28......................| 57 | 48 | 9

June 15......................| 64 | 51 | 13

" 27......................| 62 | 51 | 11

July 16......................| 62 | 51 | 11

" 30......................| 65 1/2 | 55 1/2 | 10

Aug. 15......................| 68 | 58 | 10

" 31......................| 59 1/2 | 55 | 4 1/2

Sept.15......................| 59 1/2 | 55 | 4 1/2

Oct. 1......................| 59 1/2 | 55 | 4 1/2

" 15......................| 49 | 49 | 0

Nov. 1......................| 43 | 43 | 0

" 16......................| 43 1/2 | 43 1/2 | 0

On the 14th of January, 1791, in a winter remarkable for its extreme

severity, he found the ground, on a plain open field where the snow had

been blown away, frozen to the depth of three feet and five inches; in

the woods where the snow was three feet deep, and where the soil had

frozen to the depth of six inches before the snow fell, the thermometer,

at six inches below the surface of the ground, stood at 39 degrees. In

consequence of the covering of the snow, therefore, the previously

frozen ground had been thawed and raised to seven degrees above the

freezing-point.--William's Vermont, i., p. 74.

Boussingault's observations are important. Employing three

thermometers, one with the bulb an inch below the surface of powdery

snow; one on the surface of the ground beneath the snow, then four

inches deep; and one in the open air, forty feet above the ground, on

the north side of a building, he found, at 5 P.M., the FIRST

thermometer at -1.5 degrees Centigrade, the second at 0 degrees, and

the THIRD at + 2.5 degrees; at 7 A.M. the next morning, the first stood

at -12 degrees, the second at -3.5 degrees and the third at -3 degrees;

at 5.30 the same evening No. 1 stood at -1.4 degrees, No. 2 at 0

degrees, and No. 3 at + 3 degrees. Other experiments were tried, and

though the temperature was affected by the radiation, which varied with

the hour of the day and the state of the sky, the upper surface of the

snow was uniformly colder than the lower, or than the open air.

According to the Report of the Department of Agriculture for May and

June, 1872, Mr. C. G. Prindle, of Vermont, in the preceding winter,

found, for four successive days, the temperature immediately above the

snow at 13 degrees below zero; beneath the snow, which was but four

inches deep, at 19 degrees above zero; and under a drift two feet deep,

at 27 degrees above.

On the borders and in the glades of the American forest, violets and

other small plants begin to vegetate as soon as the snow has thawed the

soil around their roots, and they are not unfrequently found in full

flower under two or three feet of snow.--American Naturalist, May, 1869,

pp. 155, 156.

In very cold weather, when the ground is covered with light snow, flocks

of the grouse of the Eastern States often plunge into the snow about

sunset, and pass the night in this warm shelter. If the weather

moderates before morning, a frozen crust is sometimes formed on the

surface too strong to be broken by the birds, which consequently

perish.] The snow in contact with the earth now begins to melt, with

greater or less rapidity, according to the relative temperature of the

earth and the air, while the water resulting from its dissolution is

imbibed by the vegetable mould, and carried off by infiltration so fast

that both the snow and the layers of leaves in contact with it often

seem comparatively dry, when, in fact, the under-surface of the former

is in a state of perpetual thaw. No doubt a certain proportion of the

snow is given off to the atmosphere by direct evaporation, but in the

woods, the protection against the sun by even leafless trees prevents

much loss in this way, and besides, the snow receives much moisture from

the air by absorption and condensation. Very little water runs off in

the winter by superficial water-courses, except in rare cases of sudden

thaw, and there can be no question that much the greater part of the

snow deposited in the forest is slowly melted and absorbed by the earth.

The immense importance of the forest, as a reservoir of this stock of

moisture, becomes apparent, when we consider that a large proportion of

the summer rain either flows into the valleys and the rivers, because it

falls faster than the ground can imbibe it; or, if absorbed by the warm

superficial strata, is evaporated from them without sinking deep enough

to reach wells and springs, which, of course, depend much on winter

rains and snows for their entire supply. This observation, though

specially true of cleared and cultivated grounds, is not wholly

inapplicable to the forest, particularly when, as is too often the case

in Europe, the underwood and the decaying leaves are removed.

The quantity of snow that falls in extensive forests, far from the open

country, has seldom been ascertained by direct observation, because

there are few meteorological stations in or near the forest. According

to Thompson, [Footnote: Thompson's Vermont, Appendix, p. 8.] the

proportion of water which falls in snow in the Northern States does not

exceed one-fifth of the total precipitation, but the moisture derived

from it is doubtless considerably increased by the atmospheric vapor

absorbed by it, or condensed and frozen on its surface. I think I can

say from experience--and I am confirmed in this opinion by the testimony

of competent observers whose attention has been directed specially to

the point--that though much snow is intercepted by the trees, and the

quantity on the ground in the woods is consequently less than in open

land in the first part of the winter, yet most of what reaches the

ground at that season remains under the protection of the wood until

melted, and as it occasionally receives new supplies the depth of snow

in the forest in the latter half of winter is considerably greater than

in the cleared fields. Careful measurements in a snowy region in New

England, in the month of February, gave a mean of 38 inches in the open

ground and 44 inches in the woods. [Footnote: As the loss of snow by

evaporation has been probably exaggerated by popular opinion, an

observation or two on the subject may not be amiss in this place. It is

true that in the open grounds, in clear weather and with a dry

atmosphere, snow and ice are evaporated with great rapidity even when

the thermometer is much below the freezing-point; and Darwin informs us

that the snow on the summit of Aconcagua, 23,000 feet high, and of

course in a temperature of perpetual frost, is sometimes carried off by

evaporation. The surface of the snow in our woods, however, does not

indicate much loss in this way. Very small deposits of snow-flakes

remain unevaporated in the forest, for many days after snow which fell

at the same time in the cleared field has disappeared without either a

thaw to melt it or a wind powerful enough to drift it away. Even when

bared of their leaven, the trees of a wood obstruct, in an important

degree, both the direct action of the sun's rays on the snow and the

movement of drying and thawing winds.

Dr. Piper (Trees of America, p. 48) records the following observations:

"A body of snow, one foot in depth and sixteen feet square, was

protected from the wind by a tight board fence about five feet high,

while another body of snow, much more sheltered from the sun than the

first, six feet in depth, and about sixteen feet square, was fully

exposed to the wind. When the thaw came on, which lasted about a

fortnight, the larger body of snow was entirely dissolved in less than a

week, while the smaller body was not wholly gone at the end of the

second week. "Equal quantities of snow were placed in vessels of the

samekind and capacity, the temperature of the air being seventy degrees.

In the one case, a constant current of air was kept passing over the

open vessel, while the other was protected by a cover. The snow in the

first was dissolved in sixteen minutes, while the latter had a small

unthawed proportion remaining at the end of eighty-five minutes." The

snow in the woods is protected in the same way, though not literally to

the same extent, as by the fence in one of these cases and the cover in

the other.]

The general effect of the forest in cold climates is to assimilate the

winter state of the ground to that of wooded regions under softer skies;

and it is a circumstance well worth noting, that in Southern Europe,

where Nature has denied to the earth a warm winter-garment of flocculent

snow, she has, by one of those compensations in which her empire is so

rich, clothed the hillsides with umbrella and other pines, ilexes,

cork-oaks, bays and other trees of persistent foliage, whose evergreen

leaves afford to the soil a protection analogous to that which it

derives from snow in more northern climates.

The water imbibed by the soil in winter sinks until it meets a more or

less impermeable or a saturated stratum, and then, by unseen conduits,

slowly finds its way to the channels springs, or oozes out of the ground

in drops which unite in rills, and so all is conveyed to the larger

streams, and by them finally to the sea. The water, in percolating

through the vegetable and mineral layers, acquires their temperature,

and is chemically affected by their action, but it carries very little

matter in mechanical suspension.

The process I have described is a slow one, and the supply of moisture

derived from the snow, augmented by the rains of the following seasons,

keeps the forest-ground, where the surface is level or but moderately

inclined, in a state of approximate saturation throughout almost the

whole year. [Footnote: The statements I have made, here and elsewhere,

respecting the humidity of the soil in natural forests, have been, I

understand, denied by Mr. T. Meehan, a distinguished American

naturalist, in a paper which I have not seen He is quoted as

maintaining, among other highly questionable propositions that no ground

is "so dry in its subsoil as that which sustains a forest on its

surface." In open, artificially planted woods, with a smooth and regular

surface, and especially in forests where the fallen leaves and branches

are annually burnt or carried off, both the superficial and the

subjacent strata may under certain circumstances, become dry, but this

rarely, if ever, happens in a wood of spontaneous growth, undeprived of

the protection afforded by its own droppings, and of the natural

accidents of surface which tend to the retention of water. See, on this

point, a very able article by Mr. Henry Stewart, in the New York Tribune

of November 23, 1873.] It may be proper to observe here that in Italy,

and in many parts of Spain and France, the Alps, the Apennines, and the

Pyrenees, not to speak of less important mountains, perform the

functions which provident nature has in other regions assigned to the

forest, that is, they act as reservoirs wherein is accumulated in winter

a supply of moisture to nourish the parched plains during the droughts

of summer. Hence, however enormous may be the evils which have accrued

to the above-mentioned countries from the destruction of the woods, the

absolute desolation which would otherwise have smitten them through the

folly of man, has been partially prevented by those natural

dispositions, by means of which there are stored up in the glaciers, in

the snow-fields, and in the basins of mountains and valleys, vast

deposits of condensed moisture which are afterwards distributed in a

liquid form during the season in which the atmosphere furnishes a

slender supply of the beneficent fluid so indispensable to vegetable and

animal life. [Footnote: The accumulation of snow and ice upon the Alps

and other mountains--which often fills up valleys to the height of

hundreds of feet--is due not only to the fall or congealed and

crystallized vapor in the form of snow, to the condensation of

atmospheric vapor on the surface of snow-fields and glaciers, and to a

temperature which prevents the rapid melting of snow, but also to the

well-known fact that, at least up to the height of 10,000 feet, rain and

snow are more abundant on the mountains than at lower levels.

But another reason may be suggested for the increase of atmospheric

humidity, and consequently of the precipitation of aqueous vapor on

mountain chains. In discussing the influence of mountains on

precipitation, meteorologists have generally treated the popular belief,

that mountains "attract" to them clouds floating within a certain

distance from them, as an ignorant prejudice, and they ascribe the

appearance of clouds about high peaks solely to the condensation of the

humidity of the air carried by atmospheric currents up the slopes of the

mountain to a colder temperature. But if mountains do not really draw

clouds and invisible vapors to them, they are an exception to the

universal law of attraction. The attraction of the small Mount

Shehallien was found sufficient to deflect from the perpendicular, by a

measurable quantity, a plummet weighing but a few ounces. Why, then,

should not greater masses attract to them volumes of vapor weighing many

tons, and floating freely in the atmosphere within moderate distances of

the mountains ]

Summer Rains, Importance of.

Babinet quotes a French proverb: "Summer rain wets nothing," and

explains it by saying that at that season the rainwater is "almost

entirely carried off by evaporation." "The rains of summer," he adds,

"however abundant they may be, do not penetrate the soil beyond the

depth of six or eight inches. In summer the evaporating power of the

heat is five or six times greater than in winter, and this force is

exerted by an atmosphere capable of containing five or six times as much

vapor as in winter." "A stratum of snow which prevents evaporation [from

the ground], causes almost all the water that composes it to filter into

the earth, and forms a provision for fountains, wells, and streams which

could not be furnished by any quantity whatever of summer rain. This

latter, useful to vegetation like the dew, neither penetrates the soil

nor accumulates a store to supply the springs and to be given out again

into the open air." [Footnote: Etudes et Lectures, vol. vi., p. 118. The

experiments or Johnstrup in the vicinity of Copenhagen, where the mean

annual precipitation is 23 1/2 inches, and where the evaporation must be

less than in the warmer and drier atmosphere of France, form the most

careful series of observations on this subject which I have met with.

Johnstrup found that at the depth at a metre and a half (50 inches) the

effects of rain and evaporation were almost imperceptible, and became

completely so at a depth of from two to three metres (6 1/2 to 10 feet).

During the summer half of the year the evaporation rather exceeded the

rainfall; during the winter half the entire precipitation was absorbed

by the soil and transmitted to lower strata by infiltration. The stratum

between one metre and a half (50 inches) and three metres (10 feet) from

the surface was then permanently in the condition of a saturated sponge,

neither receiving nor losing humidity during the summer half of the

year, but receiving from superior, and giving off to lower, strata an

equal amount of moisture during the winter half.--Johnstrup, Om

Fugtighedens Bezagelse i den naturlige Jordbund. Kjobenhavn, 1866.]

This conclusion, however applicable to the climate and to the soil of

France, is too broadly stated to be received as a general truth; and in

countries like the United States, where rain is comparatively rare

during the winter and abundant during the summer half of the year,

common observation shows that the quantity of water furnished by deep

wells and by natural springs depends almost as much upon the rains of

summer as upon those of the rest of the year, and consequently that a

large portion of the rain of that season must find its way into strata

too deep for the water to be wasted by evaporation.

[Footnote: According to observations at one hundred military stations in

the United States, the precipitation ranges from three and a quarter

inches at Fort Yuma in California to about seventy-two inches at Fort

Pike, Louisiana, the mean for the entire territory, not including

Alaska, being thirty-six inches. In the different sections of the Union

it is as follows:

North-eastern States.................. 41 inches,

New York.............................. 36 "

Middle States......................... 40 1/2 "

Ohio.................................. 40 "

Southern States....................... 51 "

S. W. States and Indian Territories... 39 1/2 "

Western States and Territories........ 30 "

Texas and New Mexico.................. 24 1/2 "

California............................ 18 1/2 "

Oregon and Washington Territory....... 50 "

The mountainous regions, it appears, do not recieve the greatest amount

of precipitation. The avenge downfall of the Southern States bordering

on the Atlantic and the Gulf of Mexico exceeds the mean of the whole

United States, being no less than fifty-one inches, while on the Pacific

coast it ranges from fifty to fifty-six inches.

As a general rule, it may be stated that at the stations on or near the

sea-coast the precipitation is greatest in the spring months, though

there are several exceptions to this remark, and at a large majority of

the stations the downfall is considerably greater in the summer months

than at any other season.]

Dalton's experiments in the years 1796, 1797, and 1798 appeared to show

that the mean absorption of the downfall by the earth in those years was

twenty-nine per cent.

Dickinson, employing the same apparatus for eight years, found the

absorption to vary widely in different years, the mean being forty-seven

per cent.

Charnock's experiments in two years show an absorption of from seventeen

to twenty-seven per cent.] Besides, even admitting that the water from

summer rains is so completely evaporated as to contribute nothing

directly to the supply of springs, it at least tends indirectly to

maintain their flow, because it saturates in part the atmosphere, and at

the same time it prevents the heat of the sun from drying the earth to

still greater depths, and bringing within the reach of evaporation the

moisture of strata which ordinarily do not feel the effects of solar

irradiation.

Influence of the Forest on the Flow of Springs.

It is an almost universal and, I believe, well-founded opinion, that the

protection afforded by the forest against the escape of moisture from

its soil by superficial flow and evaporation insures the permanence and

regularity of natural springs, not only within the limits of the wood,

but at some distance beyond its borders, and thus contributes to the

supply of an element essential to both vegetable and animal life. As the

forests are destroyed, the springs which flowed from the woods, and,

consequently, the greater water-courses fed by them, diminish both in

number and in volume. This fact is so familiar throughout the American

States and the British Provinces, that there are few old residents of

the interior of those districts who are not able to testify to its truth

as a matter of personal observation. My own recollection suggests to me

many instances of this sort, and I remember one case where a small

mountain spring, which disappeared soon after the clearing of the ground

where it rose, was recovered about twenty years ago, by simply allowing

the bushes and young trees to grow up on a rocky knoll, not more than

half an acre in extent, immediately above the spring. The ground was

hardly shaded before the water reappeared, and it has ever since

continued to flow without interruption. The hills in the Atlantic States

formerly abounded in springs and brooks, but in many parts of these

States which were cleared a generation or two ago, the hill-pastures now

suffer severely from drought, and in dry seasons furnish to cattle

neither grass nor water.

Almost every treatise on the economy of the forest adduces facts in

support of the doctrine that the clearing of the woods tends to diminish

the flow of springs and the humidity of the soil, and it might seem

unnecessary to bring forward further evidence on this point. [Footnote:

"Why go so far for the proof of a phenomenon that is repeated every day

under our own eyes, and of which every Parisian may convince himself,

without venturing beyond the Bois de Boulogne or the forest of Meudon

Let him, after a few rainy days, pass alone the Chevreuse road, which is

bordered on the right by the wood, on the left by cultivated fields. The

fall of water and the continuance of the rain have been the same on both

sides; but the ditch on the side of the forest will remain filled with

water proceeding from the infiltration through the wooded soil, long

after the other, contiguous to the open ground, has performed its office

of drainage and become dry. The ditch on the left will have discharged

in a few hours a quantity of water, which the ditch on the right

requires several days to receive and carry down to the valley."--Clave,

Etudes, etc., pp. 53, 54.] But the subject is of too much practical

importance and of too great philosophical interest to be summarily

disposed of; and it ought to be noticed that there is at least one

case--that of some loose sandy soils which, as observed by

Valles, [Footnote: Valles, Etudes sur les Inondations, p. 472.] when

bared of wood very rapidly absorb and transmit to lower strata the water

they receive from the atmosphere--where the removal of the forest may

increase the flow of springs at levels below it, by exposing to the rain

and melted snow a surface more bibulous, and at the same time less

retentive, than its original covering. Under such circumstances, the

water of precipitation, which had formerly been absorbed by the

vegetable mould and retained until it was evaporated, might descend

through porous earth until it meets an impermeable stratum, and then be

conducted along it, until, finally, at the outcropping of this stratum,

it bursts from a hillside as a running spring. But such instances are

doubtless too rare to form a frequent or an important exception to the

general law, because it is very seldom the case that such a soil as has

just been supposed is covered by a layer of vegetable earth thick enough

to retain, until it is evaporated, all the rain that falls upon it,

without imparting any water to the strata below it.

If we look at the point under discussion as purely a question of fact,

to be determined by positive evidence and not by argument, the

observations of Boussingault are, both in the circumstances they detail

and in the weight to be attached to the testimony, among the most

important yet recorded. The interest of the question will justify me in

giving, nearly in Boussingault's own words, the facts and some of the

remarks with which he accompanies the detail of them. "In many

localities," he observes, [Footnote: Economie Rurale t. ii, p. 780.] "it

has been thought that, within a certain number of years, a sensible

diminution has been perceived in the volume of water of streams utilized

as a motive-power; at other points, there are grounds for believing that

rivers have become shallower, and the increasing breadth of the belt of

pebbles along their banks seems to prove the loss of a part of their

water; and, finally, abundant springs have almost dried up. These

observations have been principally made in valleys bounded by high

mountains, and it has been noticed that this diminution of the waters

has immediately followed the epoch when the inhabitants have begun to

destroy, unsparingly, the woods which were spread over the face of the

land. "And here lies the practical point of the question; for if it is

once established that clearing diminishes the volume of streams, it is

less important to know to what special cause this effect is due. The

rivers which rise within the valley of Aragua, having no outlet to the

ocean, form, by their union, the Lake of Tacarigua or Valencia, having a

length of about two leagues and a half [= 7 English miles].

At the time of Humboldt's visit to the valley of Aragua, the

inhabitants were struck by the gradual diminution which the lake had

been undergoing for thirty years. In fact, by comparing the

descriptions given by historians with its actual condition, even making

large allowance for exaggeration, it was easy to see that the level was

considerably depressed. The facts spoke for themselves. Oviedo, who,

toward the close of the sixteenth century, had often traversed the

valley of Aragua, says positively that New Valencia was founded, in

1555, at half a league from the Lake of Tacarigua; in 1800, Humboldt

found this city 5,260 metres [= 3 1/2 English miles] from the shore.

"The aspect of the soil furnished new proofs. Many hillocks on the plain

retain the name of islands, which they more justly bore when they were

surrounded by water. The ground laid bare by the retreat of the lake was

converted into admirable plantations; and buildings erected near the

lake showed the sinking of the water from year to year. In 1796, new

islands made their appearance. A fortress built in 1740 on the island of

Cabrera, was now on a peninsula; and, finally, on two granitic islands,

those of Cura and Cabo Blanco, Humboldt observed among the shrubs, somo

metres above the water, fine sand filled with helicites.

"These clear and positive facts suggested numerous explanations, all

assuming a subterranean outlet, which permitted the discharge of the

water to the ocean. Humboldt disposed of these hypotheses, and did not

hesitate to ascribe the diminution of the waters of the lake to the

numerous clearings which had been made in the valley of Aragua within

half a century."

Twenty-two years later, Boussingault explored the valley of Aragua. For

some years previous, the inhabitants had observed that the waters of the

lake were no longer retiring, but, on the contrary, were sensibly

rising. Grounds, not long before occupied by plantations, were

submerged. The islands of Nuevas Aparecidas, which appeared above the

surface in 1796, had again become shoals dangerous to navigation.

Cabrera, a tongue of land on the north side of the valley, was so narrow

that the least rise of the water completely inundated it. A protracted

north wind sufficed to flood the road between Maracay and New Valencia.

The fears which the inhabitants of the shores had so long entertained

were reversed. Those who had explained the diminution of the lake by the

supposition of subterranean channels were suspected of blocking them up,

to prove themselves in the right.

During the twenty-two years which had elapsed, the valley of Aragua had

been the theatre of bloody struggles, and war had desolated these

smiling lands and decimated their population. At the first cry of

independence a great number of slaves found their liberty by enlisting

under the banners of the new republic; the great plantations were

abandoned, and the forest, which in the tropics so rapidly encroaches,

had soon recovered a large proportion of the soil which man had wrested

from it by more than a century of constant and painful labor.

Boussingault proceeds to state that two lakes near Ubate, in New

Granada, had formed but one, a century before his visit; that the waters

were gradually retiring, and the plantations extending over the

abandoned bed; that, by inquiry of old hunters and by examination of

parish records, he found that extensive clearings had been made and were

still going on.

He found, also, that the length of the Lake of Fuquene, in the same

valley, had, within two centuries, been reduced from ten leagues to one

and a half, its breadth from three leagues to one. At the former period,

the neighboring mountains were well wooded, but at the time of his visit

the mountains had been almost entirely stripped of their wood. Our

author adds that other cases, similar to those already detailed, might

be cited, and he proceeds to show, by several examples, that the waters

of other lakes in the same regions, where the valleys had always been

bare of wood, or where the forests had not been disturbed, had undergone

no change of level.

Boussingault further states that the lakes of Switzerland have sustained

a depression of level since the too prevalent destruction of the woods,

and arrives at the general conclusion that, "in countries where great

clearings have been made, there has most probably been a diminution in

the living waters which flow upon the surface of theground." This

conclusion he further supports by two examples: one, where a fine

spring, at the foot of a wooded mountain in the Island of Ascension,

dried up when the mountain was cleared, but reappeared when the wood was

replanted; the other at Marmato, in the province of Popayan, where the

streams employed to drive machinery were much diminished in volume,

within two years after the clearing of the heights from which they

derived their supplies. This latter is an interesting case, because,

although the rain-gauges, established as soon as the decrease of water

began to excite alarm, showed a greater fall of rain for the second year

of observation than the first, yet there was no appreciable increase in

the flow of the mill-streams. From these cases, the distinguished

physicist infers that very restricted local clearings may diminish and

even suppress springs and brooks, without any reduction in the total

quantity of rain.

It will have been noticed that these observations, with the exception of

the last two cases, do not bear directly upon the question of the

diminution of springs by clearings, but they logically infer it from the

subsidence of the natural reservoirs which springs once filled. There

is, however, no want of positive evidence on this subject. Marchand

cites the following instances: "Before the felling of the woods, within

the last few years, in the valley of the Soulce, the Combe-es-Monnin and

the Little Valley, the Sorne furnished a regular and sufficient supply

of water for the ironworks of Unterwyl, which was almost unaffected by

drought or by heavy rains. The Sorne has now become a torrent, every

shower occasions a flood, and after a few days of fine weather, the

current falls so low that it has been necessary to change the

water-wheels, because those of the old construction are no longer able

to drive the machinery, and at last to introduce a steam-engine to

prevent the stoppage of the works for want of water.

"When the factory of St. Ursanne was established, the river that

furnished its power was abundant, and had, from time immemorial,

sufficed for the machinery of a previous factory. Afterwards, the woods

near its sources were cut. The supply of water fell off in consequence,

the factory wanted water for half the year, and was at last obliged to

stop altogether.

"The spring of Combefoulat, in the commune of Seleate, was well known as

one of the best in the country; it was remarkably abundant, and

sufficient, in the severest droughts, to supply all the fountains of the

town; but as soon as considerable forests were felled in Combe-de-pre

Martin and in the valley of Combefoulat, the famous spring, which lies

below these woods, has become a mere thread of water, and disappears

altogether in times of drought.

"The spring of Varieux, which formerly supplied the castle of Pruntrut,

lost more than half its water after the clearing of Varieux and

Rougeoles. These woods have been replanted, the young trees are growing

well, and, with the woods, the waters of the spring are increasing.

"The Dog Spring between Pruntrut and Bressancourt has entirely vanished

since the surrounding forest-grounds were brought under cultivation.

"The Wolf Spring, in the commune of Soubey, furnishes a remarkable

example of the influence of the woods upon fountains. A few years ago

this spring did not exist. At the place where it now rises, a small

thread of water was observed after very long rains, but the stream

disappeared with the rain. The spot is in the middle of a very steep

pasture inclining to the south. Eighty years ago, the owner of the land,

perceiving that young firs were shooting up in the upper part of it,

determined to let them grow, and they soon formed a flourishing grove.

As soon as they were well grown, a fine spring appeared in place of the

occasional rill, and furnished abundant water in the longest droughts.

For forty or fifty years this spring was considered the best in the Clos

du Doubs. A few years since, the grove was felled, and the ground turned

again to a pasture. The spring disappeared with the wood, and is now as

dry as it was ninety years ago." [Footnote: Ueber Die Entwaldung Der

Gebirge, pp. 20 et seqq.]

Siemoni gives the following remarkable facts from his own personal

observation:

"In a rocky nook near the crest of a mountain in the Tuscan Apennines,

there flowed a clear, cool, and perennial fountain, uniting three

distinct springs in a single current. The ancient beeches around and

particularly above the springs were felled. On the disappearance of the

wood, the springs ceased to flow, except in a thread of water in rainy

weather, greatly inferior in quality to that of the old fountain. The

beeches were succeeded by firs, and as soon as they had grown

sufficiently to shade the soil, the springs begun again to flow, and

they gradually returned to their former abundance and quality."

[Footnote: Manuale D'arte Forestale. 2me editione, p. 492.]

This and the next preceding case are of great importance both as to the

action of the wood in maintaining springs, and particularly as tending

to prove that evergreens do not exercise the desiccative influence

ascribed to them in France. The latter instance shows, too, that the

protective influence of the wood extends far below the surface, for the

quality of the water was determined, no doubt, by the depth from which

it was drawn. The slender occasional supply after the beeches were cut

was rain-water which soaked through the superficial humus and oozed out

at the old orifices, carrying the taste and temperature of the vegetable

soil with it; the more abundant and grateful water which flowed before

the beeches were cut, and after the firs were well grown, came from a

deeper source and had been purified, and cooled to the mean temperature

of the locality, by filtering through strata of mineral earth. "The

influence of the forest on springs," says Hummel, "is strikingly shown

by an instance at Heilbronn. The woods on the hills surrounding the town

are cut in regular succession every twentieth year. As the annual

cuttings approach a certain point, the springs yield less water, some of

them none at all; but as the young growth shoots up, they flow more and

more freely, and at length bubble up again in all their original

abundance." [Footnote: Physische Geographie, p. 32.] Dr. Piper states

the following case: "Within about half a mile of my residence there is

a pond upon which mills have been standing for a long time, dating back,

I believe, to the first settlement of the town. These have been kept in

constant operation until within some twenty or thirty years, when the

supply of water began to fail. The pond owes its existence to a stream

that has its source in the hills which stretch some miles to the south.

Within the time mentioned, these hills, which were clothed with a dense

forest, have been almost entirely stripped of trees; and to the wonder

and loss of the mill-owners, the water in the pond has failed, except in

the season of freshets; and, what was never heard of before, the stream

itself has been entirely dry. Within the last ten years a new growth of

wood has sprung up on most of the land formerly occupied by the old

forest; and now the water runs through the year, notwithstanding the

great droughts of the last few years, going back from 1856."

Dr. Piper quotes from a letter of William C. Bryant the following

remarks: "It is a common observation that our summers are becoming drier

and our streams smaller. Take the Cuyahoga as an illustration. Fifty

years ago large barges loaded with goods went up and down that river,

and one of the vessels engaged in the battle of Lake Erie, in which the

gallant Perry was victorious, was built at Old Portage, six miles north

of Albion, and floated down to the lake. Now, in an ordinary stage of

the water, a canoe or skiff can hardly pass down the stream. Many a boat

of fifty tons burden has been built and loaded in the Tuscarawas, at New

Portage, and sailed to New Orleans without breaking bulk. Now, the river

hardly affords a supply of water at New Portage for the canal. The same

may be said of other streams--they are drying up. And from the same

cause--the destruction of our forests--our summers are growing drier and

our winters colder." [Footnote: The Trees of America, pp. 50, 51.]

No observer has more carefully studied the influence of the forest upon

the flow of the waters, or reasoned more ably on the ascertained

phenomena, than Cantegril. The facts presented in the following case,

communicated by him to the Ami des Sciences for December, 1859, are as

nearly conclusive as any single instance well can be:

"In the territory of the commune of Labruguiere there is a forest of

1,834 hectares [4,530 acres], known by the name of the Forest of

Montaut, and belonging to that commune. It extends along thenorthern

slope of the Black Mountains. The soil is granitic, the maximum altitude

1,243 metres [4,140 feet], and the inclination ranges between 15 and 60

to 100.

"A small current of water, the brook of Caunan, takes its rise in this

forest, and receives the waters of two-thirds of its surface. At the

lower extremity of the wood and on the stream are several fulleries,

each requiring a force of eight horse-power to drive the water-wheels

which work the stampers. The commune of Labruguiere had been for a long

time famous for its opposition to forest laws. Trespasses and abuses of

the right of pasturage had converted the wood into an immense waste, so

that this vast property now scarcely sufficed to pay the expense of

protecting it, and to furnish the inhabitants with a meagre supply of

fuel. While the forest was thus ruined, and the soil thus bared, the

water, after every abundant rain, made an eruption into the valley,

bringing down a great quantity of pebbles which still clog the current

of the Caunan. The violence of the floods was sometimes such that they

were obliged to stop the machinery for some time. During the summer

another inconvenience was felt. If the dry weather continued a little

longer than usual, the delivery of water became insignificant. Each

fullery could for the most part only employ a single set of stampers,

and it was not unusual to see the work entirely suspended.

"After 1840, the municipal authority succeeded in enlightening the

population as to their true interests. Protected by a more watchful

supervision, aided by well-managed replantation, the forest has

continued to improve to the present day. In proportion to the

restoration of the forest, the condition of the manufactories has become

less and less precarious, and the action of the water is completely

modified. For example, sudden and violent floods, which formerly made it

necessary to stop the machinery, no longer occur. There is no increase

in the delivery until six or eight hours after the beginning of the

rain; the floods follow a regular progression till they reach their

maximum, and decrease in the same manner. Finally, the fulleries are no

longer forced to suspend work in summer; the water is always

sufficiently abundant to allow the employment of two sets of stampere at

least, and often even of three.

"This example is remarkable in this respect, that, all other

circumstances having remained the same, the changes in the action of the

stream can be attributed only to the restoration of the forest--changes

which may be thus summed up: diminution of flood-water during

rains--increase of delivery at other seasons."

Becquerel and other European writers adduce numerous other cases where

the destruction of forests has caused the disappearance of springs, a

diminution in the volume of rivers, and a lowering of the level of

lakes, and in fact, the evidence in support of the doctrine I have been

maintaining on this subject seems to be as conclusive as the nature of

the case admits. [Footnote: See, in the Revue des Eaux et Forets for

April, 1867, an article entitled De l'influence des Forets sur le Regime

des Eaux, and the papers in previous numbers of the same journal therein

referred to.] We cannot, it is true, arrive at the same certainty and

precision of result in these inquiries as in those branches of physical

research where exact quantitative appreciation is possible, and we must

content ourselves with probabilities and approximations. We cannot

positively affirm that the precipitation in a given locality is

increased by the presence, or lessened by the destruction, of the

forest, and from our ignorance of the subterranean circulation of the

waters, we cannot predict, with certainty, the drying up of a particular

spring as a consequence of the felling of the wood which shelters it;

but the general truth, that the flow of springs and the normal volume of

rivers rise and fall with the extension and the diminution of the woods

where they originate and through which they run, is as well established

as any proposition in the science of physical geography. [Footnote: Some

years ago it was popularly believed that the volume of the Mississippi,

like that of the Volga and other rivers of the Eastern Hemisphere, was

diminished by the increased evaporation from its basin and the drying up

of the springs in consequence of the felling of the forests in the

vicinity of the source of its eastern affluents. The boatmen of this

great river and other intelligent observers now assure us, however, that

the mean and normal level of the Mississippi has risen within a few

years, and that in consequence the river is navigable at low water for

boats of greater draught and at higher points in its course than was the

case twenty-five years ago. This supposed increase of volume has been

attributed by some to the recent re-wooding of the prairies, but the

plantations thus far made are not yet sufficiently extensive to produce

an appreciable effect of this nature; and besides, while young trees

have covered some of the prairies, the destruction of the forest has

been continued perhaps in a greater proportion in other parts of the

basin of the river. A more plausible opinion is that the substitution of

ground that is cultivated, and consequently spongy and absorbent, for

the natural soil of the prairies, has furnished a reservoir for the

rains which are absorbed by the earth and carried gradually to the river

by subterranean flow, instead of running off rapidly from the surface,

or, as is more probable, instead of evaporating or being taken up by the

vigorous herbaceous vegetation which covers the natural prairie.

A phenomenon so contrary to common experience, as would be a permanent

increase in the waters of a great river, will not be accepted without

the most convincing proofs. The present greater facility of navigation

may be attributed to improvements in the model of the boats, to the

removing of sand-banks and other impediments to the flow of the waters,

or to the confining of these waters in a narrower channel, by extending

the embankments of the river, or to yet other causes. So remarkable a

change could not have escaped the notice of Humphreys and Abbot, whose

most able labors comprise the years 1850-1861, had it occurred during

that period or at any former time within the knowledge of the many

observers they consulted; but no such fact is noticed in their

exhaustive report. However, even if an increase in the volume of the

Mississippi, for a period of ten or twenty years, were certain, it would

still be premature to consider this increase as normal and constant,

since it might very well be produced by causes yet unknown and analogous

to those which influence the mysterious advance and retreat of those

Alpine ice-rivers, the glaciers. Among such causes we may suppose a long

series of rainy seasons in regions where important tributaries have

their far-off and almost unknown sources; and with no less probability,

we may conceive of the opening of communications with great subterranean

reservoirs, which may from year to year empty large quantities of water

into the bed of the stream; or the closing up of orifices through which

a considerable portion of the water of the river once made its way for

the supply of such reservoirs.--See upon this point, Chap. IV., Of

Subterranean Waters; post.]

Of the converse proposition, namely, that the planting of new forests

gives rise to new springs and restores the regular flow of rivers, I

find less of positive proof, however probable it may be that such

effects would follow. [Footnote: According to the Report of the

Department of Agriculture for February, 1872, it is thought in the Far

West that the young plantations have already influenced the

water-courses in that region, and it is alleged that ancient river-beds,

never known to contain water since the settlement of the country, have

begun to flow since these plantations were commenced. See also Hayden,

Report on Geological Survey of Wyoming, 1870, p. 104, and Bryant. Forest

Trees, 1871, chap. iv.

In the Voyage autour du Monde of the Comte da Beauvoir, chap. x., this

passage occurs: Dr. Muller, Director of the Botanic Garden at Melbourne,

"has distributed through the interior of Australia millions of seedling

trees from his nursuries. Small rivulets are soon formed under the young

wood; the results are superb, and the observation of every successive

year confirms them. On bare soils he has created, at more than a hundred

points, forests and water-courses."] A reason for the want of evidence

on the subject may be, that, under ordinary circumstances, the process

of conversion of bare ground to soil with a well-wooded surface is so

gradual and slow, and the time required for a fair experiment is

consequently so long, that many changes produced by the action of the

new geographical element escape the notice and the memory of ordinary

observers. The growth of a forest, including the formation of a thick

stratum of vegetable mould beneath it, is the work of a generation, its

destruction may be accomplished in a day; and hence, while the results

of the one process may, for a considerable time, be doubtful if not

imperceptible, those of the other are immediate and readily appreciable.

Fortunately, the plantation of a wood produces other beneficial

consequences which are both sooner realized and more easily estimated;

and though he who drops the seed is sowing for a future generation as

well as for his own, the planter of a grove may hope himself to reap a

fair return for his expenditure and his labor.

Influence of the Forest on Inundations and Torrents.

Inasmuch as it is not yet proved that the forests augment or diminish

the precipitation in the regions they principally cover, we cannot

positively affirm that their presence or absence increases or lessens

the total volume of the water annually delivered by great rivers or by

mountain torrents. It is nevertheless certain that they exercise an

action on the discharge of the water of rain and snow into the valleys,

ravines, and other depressions of the surface, where it is gathered into

brooks and finally larger currents, and consequently influence the

character of floods, both in rivers and in torrents. For this reason,

river inundations and the devastations of torrents, and the geographical

effects resulting from them, so far as they are occasioned or modified

by the action of forests or of the destruction of the woods, may

properly be discussed in this chapter, though they might seem otherwise

to belong more appropriately to another division of this work.

Besides the climatic question, which I have already sufficiently

discussed, and the obvious inconveniences of a scanty supply of

charcoal, of fuel, and of timber for architectural and naval

construction and for the thousand other uses to which wood is applied in

rural and domestic economy, and in the various industrial processes of

civilized life, the attention of European foresters and public

economists has been specially drawn to three points, namely: the

influence of the forests on the permanence and regular flow of springs

or natural fountains; on inundations by the overflow of rivers; and on

the abrasion of soil and the transportation of earth, gravel, pebbles,

and even of considerable masses of rock, from higher to lower levels, by

torrents. There are, however, connected with this general subject,

several other topics of minor or strictly local interest, or of more

uncertain character, which I shall have occasion more fully to speak of

hereafter.

The first of these three principal subjects--the influence of the woods

on springs and other living waters--has been already considered; and if

the facts stated in that discussion are well established, and the

conclusions I have drawn from them are logically sound, it would seem to

follow, as a necessary corollary, that the action of the forest is as

important in diminishing the frequency and violence of river-floods as

in securing the permanence and equability of natural fountains; for any

cause which promotes the absorption and accumulation of the water of

precipitation by the superficial strata of the soil, to be slowly given

out by infiltration and percolation, must, by preventing the rapid flow

of surface-water into the natural channels of drainage, tend to check

the sudden rise of rivers, and, consequently, the overflow of their

banks, which constitutes what is called inundation.

The surface of a forest, in its natural condition, can never pour forth

such deluges of water as flow from cultivated soil. Humus, or vegetable

mould, is capable of absorbing almost twice its own weight of water. The

soil in a forest of deciduous foliage is composed of humus, more or less

unmixed, to the depth of several inches, sometimes even of feet, and

this stratum is usually able to imbibe all the water possibly resulting

from the snow which at any one time covers, or the rain which in any one

shower falls upon it. But the vegetable mould does not cease to absorb

water when it becomes saturated, for it then gives off a portion of its

moisture to the mineral earth below, and thus is ready to receive a new

supply; and, besides, the bed of leaves not yet converted to mould takes

up and retains a very considerable proportion of snow-water, as well as

of rain.

The stems of trees, too, and of underwood, the trunks and stumps and

roots of fallen timber, the mosses and fungi and the numerous

inequalities of the ground observed in all forests, oppose a mechanical

resistance to the flow of water over the surface, which sensibly retards

the rapidity of its descent down declivities, and diverts and divides

streams which may have already accumulated from smaller threads of

water. [Footnote: In a letter addressed to the Minister of Public Works,

after the terrible inundations of 1857, the late Emperor of France thus

happily expressed himself: "Before we seek the remedy for an evil, we

inquire into its cause. Whence come the sudden floods of our rivers From

the water which falls on the mountains, not from that which falls on the

plains. The waters which fall on our fields produce but few rivulets,

but these which fall on our roofs and are collected in the gutters, form

small streams at once. Now, the roofs are mountains--the gutters are

valleys."

"To continue the comparison," observes D'Hericourt, "roofs are smooth

and impermeable, and the rain-water pours rapidly off from their

surfaces; but this rapidity of flow would be greatly diminished if the

roofs were carpeted with mosses and grasses; more still, if they were

covered with dry leaves, little shrubs, strewn branches, and other

impediments--in short, if they were wooded."--Annales Forestieres, Dec.

1857, p. 311.

The mosses and fungi play a more important part in regulating the

humidity of the air and of the soil than writers on the forest have

usually assigned to them. They perish with the trees they grow on; but,

in many situations, nature provides a compensation for the tree-mosses

and fungi in ground species, which, on cold soils, especially those with

a northern exposure, spring up abundantly both before the woods are

felled, and when the land is cleared and employed for pasturage, or

deserted. These humble plants discharge a portion of the functions

appropriated to the wood, and while they render the soil of improved

lands much less fit for agricultural use, they, at the same time,

prepare it for the growth of a new harvest of trees, when the

infertility they produce shall have driven man to abandon it and suffer

it to relapse into the hands of nature.

In primitive forests, when the ground is not too moist to admit of a

dense growth of trees, the soil is generally so thickly covered with

leaves that there is little room for ground mosses and mushrooms. In the

more open artificial woods of Europe these forms of vegetation, as well

as many more attractive plants, are more frequent than in the native

groves of America. See, on cryptogamic and other wood plants,

Rossmassler, Der Wald, pp. 82 et seqq., and on the importance of such

vegetables in checking the flow of water, Mengotti, Idraulica Fisica e

Sperimentale, chapters xvi. and xvii. No writer known to me has so well

illustrated this function of forest vegetation as Mengotti, though both

he and Rossmassler ascribe to plants a power of absorbing water from the

atmosphere which they do not possess, or rather can only rarely

exercise.]

The value of the forest as a mechanical check to a too rapid discharge

of rain-water was exemplified in numerous instances in the great floods

of 1866 and 1868, in France and Switzerland, and I refer to the

observations made on those occasions as of special importance because no

previous inundations in those countries had been so carefully watched

and so well described by competent investigators. In the French

Department of Lozere, which was among those most severely injured by the

inundation of 1866--an inundation caused by diluvial rains, not by

melted snow--it was everywhere remarked that "grounds covered with wood

sustained no damage even on the steepest slopes, while in cleared and

cultivated fields the very soil was washed away and the rocks laid bare

by the pouring rain." [Footnote: See, for other like observations, an

article entitled Le Reboisement et les Inondations, in the Revue des

Eaux et Forets of September, 1868]

The Italian journals of the day state that the province of Brescia and a

part of that of Bergamo, which have heretofore been exposed to enormous

injury, after every heavy rain, from floods of the four principal

streams which traverse them, in a great degree escaped damage in the

terrible inundation of October, 1872, and their immunity is ascribed to

the forestal improvements executed by the former province, within ten or

twelve years, in the Val Camonica and in the upper basins of the other

rivers which drain that territory. Similar facts were noticed in the

extraordinary floods of September and October, 1868, in the valley of

the Upper Rhine, and Coaz makes the interesting observation that not

even dense greensward was so efficient a protection to the earth as

trees, because the water soaked through the sod and burst it up by

hydrostatic pressure. [Footnote: Die Hochwasser in 1868 im Bandnerischen

Rheingebiet, pp. 12, 68.

Observations of Forster, cited by Cezanne from the Annales Forestieres

for 1859, p. 358, are not less important than those adduced in the text.

The field of these observations was a slope of 45 degrees divided into

three sections, one luxuriantly wooded from summit to base with oak and

beech, one completely cleared through its whole extent, and one cleared

in its upper portion, but retaining a wooded belt for a quarter of the

height of the slope, which was from 1,360 to 1,800 feet above the brook

at its foot.

In the first section, comprising six-sevenths of the whole surface, the

rains had not produced a single ravine; in the second, occupying about a

tenth of the ground, were three ravines, increasing in width from the

summit to the valley beneath, where they had, all together, a

cross-section of 600 square feet; in the third section, of about the

same extent as the second, four ravines had been formed, widening from

the crest of the slope to the belt of wood, where they gradually

narrowed and finally disappeared.

For important observations to the same purpose, see Marchand, Les

Torrents des Alpes, in Revue des Eaux et Forets for September, 1871.]

The importance of the mechanical resistance of the wood to the flow of

water OVER THE SURFACE has, however, been exaggerated by some writers.

Rain-water is generally absorbed by the forest-soil as fast as it falls,

and it is only in extreme cases that it gathers itself into a

superficial sheet or current overflowing the ground. There is,

nevertheless, besides the absorbent power of the soil, a very

considerable mechanical resistance to the transmission of water BENEATH

the surface through and along the superior strata of the ground. This

resistance is exerted by the roots, which both convey the water along

their surface downwards, and oppose a closely wattled barrier to its

descent along the slope of the permeable strata which have absorbed it.

[Footnote: In a valuable report on a bill for compelling the sale of

waste communal lands, now pending in the Parliament of Italy, Senator

Torelli, an eminent man of science, calculates that four-fifths of the

precipitation in the forest are absorbed by the soil, or detained by the

obstructions of the surface, only one-fifth being delivered to the

rivers rapidly enough to create danger of floods, while in open grounds,

in heavy rains, the proportions are reversed. Supposing a rain-fall of

four inches, an area measuring 100,000 acres, or a little more than four

American townships, would receive 53,777,777 cubic yards of water. Of

this quantity it would retain, or rather detain, if wooded, 41,000,000

yards, if bare, only 11,000,000. The difference of discharge from wooded

and unwooded soils is perhaps exaggerated in Col. Torelli's report, but

there is no doubt that in very many cases it is great enough to prevent,

or to cause, destructive inundations.] Rivers fed by springs and shaded

by woods are comparatively uniform in volume, in temperature, and in

chemical composition. [Footnote: Dumont gives an interesting extract

from the Misopogon of the Emperor Julian, showing that, in the fourth

century, the Seine--the level of which now varies to the extent of

thirty feet between extreme high and extreme low water mark--was almost

wholly exempt from inundations, and flowed with a uniform current

through the whole year. "Ego olim eram in hibernis apud curam Lutetiam,

[sic] enim Galli Parisiorum oppidum appellant, quae insula est non

magna, in fluvio sita, qui eam omni ex parte cingit. Pontes sublicii

utrinque ad eam ferunt, raroque fluvius minuitur ac crescit; sed qualis

aestate talis esse solet hyeme."--Des Travaux Publics dans leur Rapports

avec l'Agriculture, p. 361, note.

As Julian was six years in Gaul, and his principal residence was at

Paris, his testimony as to the habitual condition of the Seine, at a

period when the provinces where its sources originate were well wooded,

is very valuable.] Their banks are little abraded, nor are their courses

much obstructed by fallen timber, or by earth and gravel washed down

from the highlands. Their channels are subject only to slow and gradual

changes, and they carry down to the lakes and the sea no accumulation of

sand or silt to fill up their outlets, and, by raising their beds, to

force them to spread over the low grounds near their mouth. [Footnote:

Forest rivers seldom if ever form large sedimentary deposits at their

points of discharge into lakes or larger streams, such accumulations

beginning or at least advancing far more rapidly, after the valleys are

cleared.]

Causes of Inundations.

The immediate cause of river inundations is the flow of superficial and

subterranean waters into the beds of rivers faster than those channels

can discharge them. The insufficiency of the channels is occasioned

partly by their narrowness and partly by obstructions to their currents,

the most frequent of which is the deposit of sand, gravel, and pebbles

in their beds by torrential tributaries during the floods. [Footnote:

The extent of the overflow and the violence of the current in river-

floods are much affected by the amount of sedimentary matter let fall in

their channels by their affluents, which have usually a swifter flow

than the main stream, and consequently deposit more or less of their

transported material when they join its more slowly-moving waters. Such

deposits constitute barriers which at first check the current and raise

its level, and of course its violence at lower points is augmented, both

by increased volume and by the solid material it carries with it, when

it acquires force enough to sweep away the obstruction.--Risler, Sur L

influence des Forets sur les Cours d eau, in Revue des Eaux et Forets,

10th January, 1870.

In the flood of 1868 the torrent Illgraben, which had formerly spread

its water and its sediment over the surface of a vast cone of dejection,

having been forced, by the injudicious confinement of its current to a

single channel, to discharge itself more directly into the Rhone,

carried down a quantity of gravel, sand, and mud, sufficient to dam that

river for a whole hour, and in the same great inundation the flow of the

Rhine at Thusis was completely arrested for twenty minutes by a similar

discharge from the Nolla. Of course, when the dam yielded to the

pressure of the accumulated water, the damage to the country below was

far greater than it would have ben had the currents of the rivers not

been thus obstructed.--Marchand, Les Torrents des Alpes, in Revue des

Eaux et Forets, Sept., 1871.]

In accordance with the usual economy of nature, we should presume that

she had everywhere provided the means of discharging, without

disturbance of her general arrangements or abnormal destruction of her

products, the precipitation which she sheds upon the face of the earth.

Observation confirms this presumption, at least in the countries to

which I confine my inquiries; for, so far as we know the primitive

conditions of the regions brought under human occupation within the

historical period, it appears that the overflow of river-banks was much

less frequent and destructive than at the present day, or, at least,

that rivers rose and fell less suddenly, before man had removed the

natural checks to the too rapid drainage of the basins in which their

tributaries originate. The affluents of rivers draining wooded basins

generally transport, and of course let fall, little or no sediment, and

hence in such regions the special obstruction to the currents of

water-courses to which I have just alluded does not occur. The banks of

the rivers and smaller streams in the North American colonies were

formerly little abraded by the currents. [Footnote: In primitive

countries, running streams are very generally fringed by groves, for

almost every river is, as Pliny, Nat. Hist., v. 10, says of the Upper

Nile, an opifex silvarum, or, to use the quaint and picturesque language

of Holland's translation, "makes shade of woods as he goeth."] Even now

the trees come down almost to the water's edge along the rivers, in the

larger forests of the United States, and the surface of the streams

seems liable to no great change in level or in rapidity of current.

[Footnote: A valuable memoir by G. Doni, in the Rivista Forestale for

October, 1863, p. 438, is one of the best illustrations I can cite of

the influence of forests in regulating and equalizing the flow of

running water, and of the comparative action of water-courses which

drain wooded valleys and valleys bared of trees, with regard to the

erosion of their banks and the transportation of sediment.

"The Sestajone," remarks this writer, "and the Lima, are two

considerable torrents which collect the waters of two great valleys of

the Tuscan Apennines, and empty them into the Serchio. At the junction

of these two torrents, from which point the combined current takes the

name of Lima, a curious phenomenon is observed, which is in part easily

explained. In rainy weather the waters of the Sestajone are in volume

only about one-half those of the Lima, and while the current of the Lima

is turbid and muddy, that of the Sestajone appears limpid and I might

almost say drinkable. In clear weather, on the contrary, the waters of

the Sestajone are abundant and about double those of the Lima. Now the

extent of the two valleys is nearly equal, but the Sestajone winds down

between banks clothed with firs and beeches, while the Lima flows

through a valley that has been stripped of trees, and in great part

brought under cultivation."

The Sestajone and the Lima are neither of them what is technically

termed a torrent--a name strictly applicable only to streams whose

current is not derived from springs and perennial, but is the temporary

effect of a sudden accumulation of water from heavy rains or from a

rapid melting of the snows, while their beds are dry, or nearly so, at

other times. The Lima, however, in a large proportion of its course, has

the erosive character of a torrent, for the amount of sediment which it

carries down, even when it is only moderately swollen by rains,

surpasses almost everything of the kind which I have observed, under

analogous circumstances, in Italy.

Still more striking is the contrast in the regime of the Saint-Phalez

and the Combe-d'Yeuse in the Department of Vancluse, the latter of which

became subject to the most violent torrential floods after the

destruction of the woods of its basin between 1823 and 1833, but has now

been completely subdued, and its waters brought to a peaceful flow, by

replanting its valley. See Labussiere, Revue Agric. et Forestiere de

Provence, 1866, and Revue des Eaux et Forets, 1866.]

Inundations in Winter.

In the Northern United States, although inundations are not very

unfrequently produced by heavy rains in the height of summer, it will be

found generally true that the most rapid rise of the waters, and, of

course, the most destructive "freshets," as they are called in America,

are occasioned by the sudden dissolution of the snow before the open

ground is thawed in the spring. It frequently happens that a powerful

thaw sets in after a long period of frost, and the snow which had been

months in accumulating is dissolved and carried off in a few hours. When

the snow is deep, it, to use a popular expression, "takes the frost out

of the ground" in the woods, and, if it lies long enough, in the fields

also. But the heaviest snows usually fall after midwinter, and are

succeeded by warm rains or sunshine, which dissolve the snow on the

cleared land before it has had time to act upon the frost-bound soil

beneath it. In this case, the snow in the woods is absorbed as fast as

it melts, by the soil it has protected from freezing, and does not

materially contribute to swell the current of the rivers. If the mild

weather, in which great snow-storms usually occur, does not continue and

become a regular thaw, it is almost sure to be followed by drifting

winds, and the inequality with which they distribute the snow over the

cleared ground leaves the ridges of the surface-soil comparatively bare,

while the depressions are often filled with drifts to the height of many

feet. The knolls become frozen to a great depth; succeeding partial

thaws melt the surface-snow, and the water runs down into the furrows of

ploughed fields, and other artificial and natural hollows, and then

often freezes to solid ice. In this state of things, almost the entire

surface of the cleared land is impervious to water, and from the absence

of trees and the general smoothness of the ground, it offers little

mechanical resistance to superficial currents. If, under these

circumstances, warm weather accompanied by rain occurs, the rain and

melted snow are swiftly hurried to the bottom of the valleys and

gathered to raging torrents. It ought further to be considered that,

though the lighter ploughed soils readily imbibe a great deal of water,

yet grass-lands, and all the heavy and tenacious earths, absorb it in

much smaller quantities, and less rapidly than the vegetable mould of

the forest. Pasture, meadow, and clayey soils, taken together, greatly

predominate over sandy ploughed fields, in all large agricultural

districts, and hence, even if, in the case we are supposing, the open

ground chance to have boon thawed before the melting of the snow which

covers it, it is already saturated with moisture, or very soon becomes

so, and, of course, cannot relieve the pressure by absorbing more water.

The consequence is that the face of the country is suddenly flooded with

a quantity of melted snow and rain equivalent to a fall of six or eight

inches of the latter, or even more. This runs unobstructed to rivers

often still-bound with thick ice, and thus inundations of a fearfully

devastating character are produced. The ice bursts, from the hydrostatic

pressure from below, or is violently torn up by the current, and is

swept by the impetuous stream, in large masses and with resistless fury,

against banks, bridges, dams, and mills erected near them. The bark of

the trees along the rivers is often abraded, at a height of many feet

above the ordinary water-level, by cakes of floating ice, which are at

last stranded by the receding flood on meadow or ploughland, to delay,

by their chilling influence, the advent of the tardy spring.

Another important effect of the removal of the forest shelter in cold

climates may be noticed here. We have observed that the ground in the

woods either does not freeze at all, or that if frozen it is thawed by

the first considerable snow-fall. On the contrary, the open ground is

usually frozen when the first spring freshet occurs, but is soon thawed

by the warm rain and melting snow. Nothing more effectually

disintegrates a cohesive soil than freezing and thawing, and the surface

of earth which has just undergone those processes is more subject to

erosion by running water than under any other circumstances. Hence more

vegetable mould is washed away from cultivated grounds in such climates

by the spring floods than by the heaviest rain at other seasons.

In the warm climates of Southern Europe, as I have already said, the

functions of the forest, so far as the disposal of the water of

precipitation is concerned, are essentially the same at all seasons, and

are analogous to those which it performs in the Northern United States

in summer. Hence, in the former countries, the winter floods have not

the characteristics which mark them in the latter, nor is the

conservative influence of the woods in winter relatively so important,

though it is equally unquestionable.

If the summer floods in the United States are attended with less

pecuniary damage than those of the Loire and other rivers of France, the

Po and its tributaries in Italy, the Emme and her sister torrents which

devastate the valleys of Switzerland, it is partly because the banks of

American rivers are not yet lined with towns, their shores and the

bottoms which skirt them not yet covered with improvements whose cost is

counted by millions, and, consequently, a smaller amount of property is

exposed to injury by inundation. But the comparative exemption of the

American people from the terrible calamities which the overflow of

rivers has brought on some of the fairest portions of the Old World, is,

in a still greater degree, to be ascribed to the fact that, with all our

thoughtless improvidence, we have not yet bared all the sources of our

streams, not yet overthrown all the barriers which nature has erected to

restrain her own destructive energies. Let us be wise in time, and

profit by the errors of our older brethren!

The influence of the forest in preventing inundations has been very

generally recognized, both as a theoretical inference and as a fact of

observation; but the eminent engineer Belgrand and his commentator

Valles have deduced an opposite result from various facts of experience

and from scientific considerations. They contend that the superficial

drainage is more regular from cleared than from wooded ground, and that

clearing diminishes rather than augments the intensity of inundations.

Neither of these conclusions appears to be warranted by their data or

their reasoning, and they rest partly upon facts, which, truly

interpreted, are not inconsistent with the received opinions on these

subjects, partly upon assumptions which are contradicted by experience.

Two of these latter are, first, that the fallen leaves in the forest

constitute an impermeable covering of the soil over, not through, which

the water of rains and of melting snows flows off, and secondly, that

the roots of trees penetrate and choke up the fissures in the rocks, so

as to impede the passage of water through channels which nature has

provided for its descent to lower strata.

As to the first of those, we may appeal to familiar facts within the

personal knowledge of every man acquainted with the operations of sylvan

nature. Rain-water never, except in very trifling quantities, flows over

the leaves in the woods in summer or autumn. Water runs over them only

in the spring, in the rare cases when they have been pressed down

smoothly and compactly by the weight of the snow--a state in which they

remain only until they are dry, when shrinkage and the action of the

wind soon roughen the surface so as effectually to stop, by absorption,

all flow of water. I have observed that when a sudden frost succeeds a

thaw at the close of the winter, after the snow has principally

disappeared, the water in and between the layers of leaves sometimes

freezes into a solid crust, which allows the flow of water over it. But

this occurs only in depressions and on a very small scale; and the ice

thus formed is so soon dissolved that no sensible effect is produced on

the escape of water from the general surface.

As to the influence of roots upon drainage, we have seen that there is

no doubt that they, independently of their action as absorbents,

mechanically promote it. Not only does the water of the soil follow them

downwards, but their swelling growth powerfully tends to enlarge, not to

obstruct, the crevices of rock into which they enter; and as the

fissures in rocks are longitudinal, not mere circular orifices, every

line of additional width gained by the growth of roots within them

increases the area of the crevice in proportion to its length.

Consequently, the widening of a fissure to the extent of one inch might

give an additional drainage equal to a square foot of open tubing.

The observations and reasonings of Belgrand and Valles, though their

conclusions have not been accepted by many, are very important in one

point of view. There writers insist much on the necessity of taking into

account, in estimating the relations between precipitation and

evaporation, the abstraction of water from the surface and

surface-currents, by absorption and infiltration--an element

unquestionably of great value, but hitherto much neglected by

meteorological inquirers, who have very often reasoned as if the

surface-earth were either impermeable to water or already saturated with

it; whereas, in fact, it is a sponge, always imbibing humidity and

always giving it off, not by evaporation only, but by infiltration and

percolation.

The remarkable historical notices of inundations in France in the Middle

Ages collected by Champion [Footnote: Les Inondations en France depuis

le VIe siecle jusqu'a nos jours, 6 vols, 8vo. Paris, 1858-64. See a very

able review of this learned and important work by Prof. Messedaglia,

read before the Academy of Agriculture at Verona in 1864.] are

considered by many as furnishing proof, that when that country was much

more generally covered with wood than it now is, destructive inundations

of the French rivers were not less frequent than they are in modern

days. But this evidence is subject to this among other objections: we

know, it is true, that the forests of certain departments of France were

anciently much more extensive than at the present day; but we know also

that in many portions of that country the soil has been bared of its

forests, and then, in consequence of the depopulation of great

provinces, left to reclothe itself spontaneously with trees, many times

during the historic period; and our acquaintance with the forest

topography of ancient Gaul or of mediaeval France is neither

sufficiently extensive nor sufficiently minute to permit us to say, with

certainty, that the sources of this or that particular river were more

or less sheltered by wood at any given time, ancient or mediaeval, than

at present. [Footnote: Alfred Maury has, nevertheless, collected, in his

erudite and able work, Les Forets de la Gaule et de l'ancienne France,

Paris, 1867, an immense amount of statistical detail on the extent, the

distribution, and the destruction of the forests of France, but it still

remains true that we can very seldom pronounce on the forestal condition

of the upper valley of a particular river at the time of a given

inundation in the ancient or the mediaeval period.] I say the sources of

the rivers, because the floods of great rivers are occasioned by heavy

rains and snows which fall in the more elevated regions around the

primal springs, and not by precipitation in the main valleys or on the

plains bordering on the lower course.

The destructive effects of inundations, considered simply as a

mechanical power by which life is endangered, crops destroyed, and the

artificial constructions of man overthrown, are very terrible. Thus far,

however, the flood is a temporary and by no means an irreparable evil,

for if its ravages end here, the prolific powers of nature and the

industry of man soon restore what had been lost, and the face of the

earth no longer shows traces of the deluge that had overwhelmed it.

Inundations have even their compensations. The structures they destroy

are replaced by better and more secure erections, and if they sweep off

a crop of corn, they not unfrequently leave behind them, as they

subside, a fertilizing deposit which enriches the exhausted field for a

succession of seasons. [Footnote: The productiveness of Egypt has been

attributed too exclusively to the fertilizing effects of the slime

deposited by the inundations of the Nile; for in that climate a liberal

supply of water would produce good crops on almost any ordinary sand,

while, without water, the richest soil would yield nothing. The sediment

deposited annually is but a very small fraction of an inch in thickness.

It is alleged that in quantity it would be hardly sufficient for a good

top-dressing, and that in quality it is not chemically distinguishable

from the soil inches or feet below the surface. But to deny, as some

writers have done, that the slime has any fertilizing properties at all,

is as great a error as the opposite one of ascribing all the

agricultural wealth of Egypt to that single cause of productiveness.

Fine soils deposited by water are almost uniformly rich in all climates;

those brought down by rivers, carried out into salt-water, and then

returned again by the tide, seem to be more permanently fertile than any

others. The polders of the Netherland coast are of this character, and

the meadows in Lincolnshire, which have been covered with slime by

warping, as it is called, or admitting water over them at high tide, are

remarkably productive.

Recent analysis is said to have detected in the water of the Nile a

quantity of organic matter--derived mainly, no doubt, from the decayed

vegetation it bears down from its tropical course--sufficiently large to

furnish an important supply of fertilizing ingredients to the soil.

It is computed that the Durance--a river fed chiefly by torrents, of

great erosive power--carries down annually solid material enough to

cover 272,000 acres of soil with a deposit of two-fifths of an inch in

thickness, and that this deposit contains, in the combination most

favorable to vegetation, more azote than 110,000 tons of guano, and more

carbon than 121,000 acres of woodland would assimilate in a year. Elisee

Reclus, La Terre, vol. i., p. 467. On the chemical composition,

quantity, and value of the solid matter transported by river, see Herve

Magnon, Sur l'Emploi des Eaux dans les Irrigations, 8vo. Paris, 1869,

pp. 132 et seqq. Duponchel, Traite d'Hydraulique et de Geologie

Agricoles. Paris, 1868, chap. i., xii., and xiii.]

If, then, the too rapid flow of the surface-waters occasioned no other

evil than to produce, once in ten years upon the average, an inundation

which should destroy the harvest of the low grounds along the rivers,

the damage would be too inconsiderable, and of too transitory a

character, to warrant the inconveniences and the expense involved in the

measures which the most competent judges in many parts of Europe believe

the respective governments ought to take to obviate it.

Destructive Action of Torrents.

But the great, the irreparable, the appalling mischiefs which have

already resulted, and which threaten to ensue on a still more extensive

scale hereafter, from too rapid superficial drainage, are of a properly

geographical, we may almost say geological, character, and consist

primarily in erosion, displacement, and transportation of the

superficial strata, vegetable and mineral--of the integuments, so to

speak, with which nature has clothed the skeleton frame-work of the

globe. It is difficult to convey by description an idea of the

desolation of the regions most exposed to the ravages of torrent and of

flood; and the thousands who, in these days of swift travel, are whirled

by steam near or even through the theatres of these calamities, have but

rare and imperfect opportunities of observing the destructive causes in

action. Still more rarely can they compare the past with the actual

condition of the provinces in question, and trace the progress of their

conversion from forest-crowned hills, luxuriant pasture grounds, and

abundant cornfields and vineyards well watered by springs and

fertilizing rivulets, to bald mountain ridges, rocky declivities, and

steep earth-banks furrowed by deep ravines with beds now dry, now filled

by torrents of fluid mud and gravel hurrying down to spread themselves

over the plain, and dooming to everlasting barrenness the once

productive fields. In surveying such scenes, it is difficult to resist

the impression that nature pronounced a primal curse of perpetual

sterility and desolation upon these sublime but fearful wastes,

difficult to believe that they wore once, and but for the folly of man

might still be, blessed with all the natural advantages which Providence

has bestowed upon the most favored climes. But the historical evidence

is conclusive as to the destructive changes occasioned by the agency of

man upon the flanks of the Alps, the Apennines, the Pyrenees, and other

mountain ranges in Central and Southern Europe, and the progress of

physical deterioration has been so rapid that, in some localities, a

single generation has witnessed the beginning and the end of the

melancholy revolution.

I have stated, in a general way, the nature of the evils in question,

and of the processes by which they are produced; but I shall make their

precise character and magnitude better understood by presenting some

descriptive and statistical details of facts of actual occurrence. I

select for this purpose the south-eastern portion of France, not because

that territory has suffered more severely than some others, but because

its deterioration is comparatively recent, and has been watched and

described by very competent and trustworthy observers, whose reports are

more easily accessible than those published in other countries.

[Footnote: Streffleur (Ueber die Natur und die Wirkungen der Wildbuche,

p. 3) maintains that all the observations and speculations of French

authors on the nature of torrents had been anticipated by Austrian

writers. In proof of this assertion he refers to the works of Franz von

Zallinger, 1778, Von Arretin, 1808, Franz Duile, 1826, all published at

Innsbruck, and Hagenus Beschreibung neuerer Wasserbauwerke, Konigsberg,

1826, none of which works are known to me. It is evident, however, that

the conclusions of Surell and other French writers whom I cite, are

original results of personal investigation, and not borrowed opinions.]