I propose now to consider one form in which the earth’s aqueous energies effect the disintegration10 and destruction of the land. The sea destroys the land slowly but surely, by beating upon its shores and by washing away the fragments shaken down from cliffs and rocks, or the more finely divided matter abstracted from softer strata11. In this work the sea is sometimes assisted by the other form of aqueous energy—the action of rain. But in the main, the sea is the destructive agent by which shore-lines are changed. The other way in which water works the destruction of the land affects the interior of land regions, or only affects the shore-line by removing earthy matter from the interior of continents to the mouths of great rivers, whence perhaps the action of the sea may carry it away to form shoals and sandbanks. I refer to the direct and indirect effects of the downfall of rain. All these effects, without a single exception, tend to level the surface of the earth. The mountain torrent12 whose colour betrays the admixture of earthy fragments is carrying those fragments from a higher to a lower level. The river owes its colour in like manner to earth which it is carrying down to the sea level. The flood deposits in valleys matter which has been withdrawn13 from hill slopes. Rainfall, acts, however, in other ways, and sometimes still more effectively. The soaked slopes of great hills give way, and great landslips occur. In winter the water which has drenched15 the land freezes, in freezing expands, and then the earth crumbles16 and is ready to be carried away by fresh rains; or when dry, by the action even of the wind alone. Landslips, too, are brought about frequently in the way, which are even more369 remarkable17 than those which are caused by the unaided action of heavy rainfalls.
The most energetic action of aqueous destructive forces is seen when water which has accumulated in the higher regions of some mountain district breaks its way through barriers which have long restrained it, and rushes through such channels as it can find or make for itself into valleys and plains at lower levels. Such catastrophes19 are fortunately not often witnessed in this country, nor when seen do they attain20 the same magnitude as in more mountainous countries. It would seem, indeed, as though they could attain very great proportions only in regions where a large extent of mountain surface lies above the snow-line. The reason why in such regions floods are much more destructive than elsewhere will readily be perceived if we consider the phenomena21 of one of these terrible catastrophes.
Take, for instance, the floods which inundated22 the plains of Martigny in 1818. Early in that year it was found that the entire valley of the Bagnes, one of the largest side-valleys of the great valley of the Rh?ne, above Geneva, had been converted into a lake through the damming up of a narrow outlet23 by avalanches25 of snow and ice from a loftier glacier26 overhanging the bed of the river Dranse. The temporary lake thus formed was no less than half a league in length, and more than 200 yards wide, its greatest depth exceeding 200 feet. The inhabitants perceived the terrible effects which must follow when the barrier burst, which it could not fail to do in the spring. They, therefore, cut a gallery 700 feet long through the ice, while as yet the water was at a moderate height. When the waters began to flow through this channel, their action widened and deepened it considerably28. At length nearly half the contents of the lake were poured off. Unfortunately, as the heat of the weather increased, the middle of the barrier slowly melted away, until it became too weak to withstand the pressure of the vast mass of water. Suddenly it gave way; and so completely that all the water in the lake rushed out in half an hour. The effects of this tremendous370 outrush of the imprisoned29 water were fearful. “In the course of their descent,” says one account of the catastrophe18, “the waters encountered several narrow gorges30, and at each of these they rose to a great height, and then burst with new violence into the next basin, sweeping31 along forests, houses, bridges, and cultivated land.” It is said by those who witnessed the passage of the flood at various parts of its course, that it resembled rather a moving mass of rock and mud than a stream of water. “Enormous masses of granite32 were torn out of the sides of the valleys, and whirled for hundreds of yards along the course of the flood.” M. Escher the engineer tells us that a fragment thus whirled along was afterwards found to have a circumference33 of no less than sixty yards. “At first the water rushed on at a rate of more than a mile in three minutes, and the whole distance (forty-five miles) which separates the Valley of Bagnes from the Lake of Geneva was traversed in little more than six hours. The bodies of persons who had been drowned in Martigny were found floating on the further side of the Lake of Geneva, near Vevey. Thousands of trees were torn up by the roots, and the ruins of buildings which had been overthrown34 by the flood were carried down beyond Martigny. In fact, the flood at this point was so high, that some of the houses in Martigny were filled with mud up to the second story.”
It is to be noted35 respecting this remarkable flood, that its effects were greatly reduced in consequence of the efforts made by the inhabitants of the lower valleys to make an outlet for the imprisoned waters. It was calculated by M. Escher that the flood carried down 300,000 cubic feet of water every second, an outflow five times as great as that of the Rhine below Basle. But for the drawing off of the temporary lake, the flood, as Lyell remarks, would have approached in volume some of the largest rivers in Europe. “For several months after the débacle of 1818,” says Lyell, “the Dranse, having no settled channel, shifted its position continually from one side to the other of the valley, carrying away newly erected36 bridges, undermining houses, and371 continuing to be charged with as large a quantity of earthy matter as the fluid could hold in suspension. I visited this valley four months after the flood, and was witness to the sweeping away of a bridge and the undermining of part of a house. The greater part of the ice-barrier was then standing37, presenting vertical38 cliffs 150 feet high, like ravines in the lava-currents of Etna, or Auvergne, where they are intersected by rivers.” It is worthy39 of special notice that inundations of similar or even greater destructiveness have occurred in the same region at former periods.
It is not, however, necessary for the destructive action of floods in mountain districts that ice and snow should assist, as in the Martigny flood. In October, 1868, the cantons of Tessin, Grisons, Uri, Valois, and St. Gall27, suffered terribly from the direct effects of heavy rainfall. The St. Gothard, Splugen, and St. Bernhardin routes were rendered impassable. In the former pass twenty-seven lives were lost, besides many horses and waggons40 of merchandise. On the three routes more than eighty persons in all perished. In the small village of Loderio alone, no less than fifty deaths occurred. The damage in Tessin was estimated at ￡40,000. In Uri and Valois large bridges were destroyed and carried away. Everything attested42 the levelling power of rain; a power which, when the rain is falling steadily43 on regions whence it as steadily flows away, we are apt to overlook.
It is not, however, necessary to go beyond our own country for evidence of the destructive action of water. We have had during the past few years very striking evidence in this respect, which need scarcely be referred to more particularly here, because it will be in the recollection of all our readers. Looking over the annals of the last half-century only, we find several cases in which the power of running water in carrying away heavy masses of matter has been strikingly shown. Consider, for instance, the effects of the flood in Aberdeenshire and the neighbouring counties, early in August, 1829. In the course of two days a great flood extended itself over “that part of the north-east of Scotland372 which would be cut off by two lines drawn14 from the head of Loch Rannoch, one towards Inverness and the other to Stonehaven.” The total length of various rivers in this region which were flooded amounted to between 500 and 600 miles. Their courses were marked everywhere by destroyed bridges, roads, buildings, and crops. Sir T. D. Lauder records “the destruction of thirty-eight bridges, and the entire obliteration44 of a great number of farms and hamlets. On the Nairn, a fragment of sandstone fourteen feet long by three feet wide and one foot thick, was carried about 200 yards down the river. Some new ravines were formed on the sides of mountains where no streams had previously45 flowed, and ancient river channels, which had never been filled from time immemorial, gave passage to a copious46 flood.” But perhaps the most remarkable effect of these inundations was the entire destruction of the bridge over the Dee at Ballater. It consisted of five arches, spanning a waterway of 260 feet. The bridge was built of granite, the pier47, resting on rolled pieces of granite and gneiss. We read that the different parts of this bridge were swept away in succession by the flood, the whole mass of masonry48 disappearing in the bed of the river. Mr. Farquharson states that on his own premises49 the river Don forced a mass of 400 or 500 tons of stones, many of them of 200 or 300 pounds’ weight, up an inclined plane, rising six feet in eight or ten yards, and left them in a rectangular heap about three feet deep on a flat ground, the heap ending abruptly50 at its lower extremity51.” At first sight this looks like an action the reverse of that levelling action which we have here attributed to water. But in reality it indicates the intense energy of this action; which drawing heavy masses down along with swiftly flowing water, communicates to them so great a momentum52, that on encountering in their course a rising slope, they are carried up its face and there left by the retreating flood. The rising of these masses no more indicates an inherent uplifting power in running water, than the ascent53 of a gently rising slope by a mass which has rolled373 headlong down the steep side of a hill indicates an upward action exerted by the force of gravity.
Even small rivers, when greatly swollen54 by rain, exhibit great energy in removing heavy masses. Thus Lyell mentions that in August, 1827, the College, a small river which flows down a slight declivity55 from the eastern watershed56 of the Cheviot Hills, carried down several thousand tons’ weight of gravel57 and sand to the plain of the Till. This little river also carried away a bridge then in process of building, “some of the arch stones of which, weighing from half to three-quarters of a ton each, were propelled two miles down the rivulet58.” “On the same occasion the current tore away from the abutment of a mill-dam a large block of greenstone porphyry, weighing nearly two tons, and transported it to a distance of nearly a quarter of a mile. Instances are related as occurring repeatedly, in which from 1000 to 3000 tons of gravel are in like manner removed by this streamlet to still greater distances in one day.”
It may appear, however, to the reader that we have in such instances as these the illustration of destructive agencies which are of their very nature limited within very narrow areas. The torrent, or even the river, may wear out its bed or widen it, but nevertheless can hardly be regarded as modifying the aspect of the region through which it flows. Even in this respect, however, the destructive action of water is not nearly so limited as it might appear to be. Taking a few centuries or a few thousand years, no doubt, we can attribute to the action of rivers, whether in ordinary flow or in flood, little power of modifying the region which they drain. But taking that wider survey (in time) of fluviatile work which modern science requires, dealing59 with this form of aqueous energy as we deal with the earth’s vulcanian energies, we perceive that the effects of river action in the course of long periods of time are not limited to the course which at any given time a river may pursue. In carrying down material along its course to the sea, a river is not merely wearing down its own bed, but is so changing it that374 in the course of time it will become unfit to drain the region through which it flows. Its bottom must of necessity become less inclined. Now although it will then be lower than at present, and therefore be then even more than now the place to which the water falling upon the region traversed by the river will naturally tend, it will no longer carry off that water with sufficient velocity61. Three consequences will follow from this state of things. In the first place there will be great destruction in the surrounding region through floods because of inadequate62 outflow; in the second place, the overflowing63 waters will in the course of time find new channels, or in other words new rivers will be formed in this region; thirdly, owing to the constant presence of large quantities of water in the depressed64 bed of the old river, the banks on either side will suffer, great landslips occurring and choking up its now useless channel. Several rivers are undergoing these changes at the present time, and others, which are manifestly unfit for the work of draining the region through which they flow (a circumstance attested by the occurrence of floods in every wet season), must before long be modified in a similar way.
We are thus led to the consideration of the second form in which the destructive action of inland waters, or we may truly say, the destructive action of rain, is manifested,—viz., in landslips. These, of course, are also caused not unfrequently by vulcanian action, but equally of course landslips so caused do not belong to our present subject. Landslips caused directly or indirectly65 by rain, are often quite as extensive as those occasioned by vulcanian energy, and they are a great deal more common. We may cite as a remarkable instance a landslip of nearly half a mile in breadth, now in progress, in a district of the city of Bath called Hedgmead, which forms a portion of the slope of Beacon66 Hill. It is attributed to the action of a subterranean67 stream on a bed of gravel, the continued washing away of which causes the shifting; but the heavy rains of 1876–77 caused the landslip to become much more marked.
375 Besides slow landslips, however, rain not unfrequently causes great masses of earth to be precipitated68 suddenly, and where such masses fall into the bed of a river, local deluges69 of great extent and of the most destructive character often follow. The following instances, cited in an abridged70 form from the pages of Lyell’s “Principles of Geology,” attest41 the terrible nature of catastrophes such as these.
Two dry seasons in the White Mountains of New Hampshire were followed by heavy rains on August 28, 1826. From the steep and lofty slopes of the River Saco great masses of rock and stone were detached, and descending71 carried along with them “in one promiscuous72 and frightful73 ruin, forests, shrubs74, and the earth which sustained them.” “Although there are numerous indications on the steep sides of these hills of former slides of the same kind, yet no tradition had been handed down of any similar catastrophe within the memory of man, and the growth of the forest on the very spots now devastated75 clearly showed that for a long interval76 nothing similar had occurred. One of these moving masses was afterwards found to have slid three miles, with an average breadth of a quarter of a mile.” At the base of the vast chasms77 formed by these natural excavations78, a confused mass of ruins was seen, consisting of transported earth, gravel, rocks, and trees. Forests were prostrated79 with as much ease as if they had been mere60 fields of grain; if they resisted for a while, “the torrent of mud and rock accumulated behind till it gathered sufficient force to burst the temporary barrier.” “The valleys of the Amonoosuck and Saco presented, for many miles, an uninterrupted scene of desolation, all the bridges being carried away, as well as those over the tributary80 streams. In some places the road was excavated81 to the depth of from fifteen to twenty feet; in others it was covered with earth, rocks, and trees to as great a height. The water flowed for many weeks after the flood, as densely82 charged with earth as it could be without being changed into mud, and marks were seen in various localities of its having risen on either side of the376 valley to more than twenty-five feet above the ordinary level.” But perhaps the most remarkable evidence of the tremendous nature of this cataclysm83 is to be found in Lyell’s statements respecting the condition of the region nineteen years later. “I found the signs of devastation84 still very striking,” he says; “I also particularly remarked that the surface of the bare granite rocks had been smoothed by the passage over them of so much mud and stone.” Professor Hubbard mentions in Silliman’s Journal that “in 1838 the deep channels worn by the avalanches of mud and stone, and the immense heaps of boulders85 and blocks of granite in the river channel, still formed a picturesque86 feature in the scenery.”
It will readily be understood that when destruction such as this follows from landslips along the borders of insignificant87 rivers, those occurring on the banks of the mighty88 rivers which drain whole continents are still more terrible. The following account from the pen of Mr. Bates the naturalist89, indicates the nature of the landslips which occur on the banks of the Amazon. “I was awoke before sunrise, one morning,” he says, “by an unusual sound resembling the roar of artillery90; the noise came from a considerable distance, one crash succeeding another. I supposed it to be an earthquake, for, although the night was breathlessly calm, the broad river was much agitated91, and the vessel92 rolled heavily. Soon afterwards another loud explosion took place, followed by others which lasted for an hour till the day dawned, and we then saw the work of destruction going forward on the other side of the river, about three miles off. Large masses of forest, including trees of colossal93 size, probably 200 feet in height, were rocking to and fro, and falling headlong one after another into the water. After each avalanche24 the wave which it caused returned on the crumbly bank with tremendous force, and caused the fall of other masses by undermining. The line of coast over which the landslip extended was a mile or two in length; the end of it, however, was hid from our view by an intervening377 island. It was a grand sight; each downfall created a cloud of spray; the concussion94 in one place causing other masses to give way a long distance from it, and thus the crashes continued, swaying to and fro, with little prospect95 of termination. When we glided96 out of sight two hours after sunrise the destruction was still going on.”
We might consider here the action of glaciers97 in gradually grinding down the mountain slopes, the destructive action of avalanches, and a number of other forms in which snow and ice break down by slow degrees the upraised portions of the earth. For in reality all these forms of destructive action take their origin in the same process whence running waters and heavy rainfalls derive98 their power. All these destructive agencies are derived99 from the vapour of water in the air. But it seems better to limit the reader’s attention in this place to the action of water in the liquid form; and therefore we proceed to consider the other ways in which rain wears down the land.
Hitherto we have considered effects which are produced chiefly along the courses of rivers, or in their neighbourhood. But heavy rainfall acts, and perhaps in the long run as effectively (when we remember the far wider region affected100) over wide tracts101 of nearly level ground, as along the banks of torrents102 and rivers.
The rain which falls on plains or gently undulating surfaces, although after a while it dries up, yet to some degree aids in levelling the land, partly by washing down particles of earth, however slowly, to lower levels, partly by soaking the earth and preparing a thin stratum103 of its upper surface to be converted into dust, and blown away by the wind. But it is when very heavy storms occur that the levelling action of rain over widely extending regions can be most readily recognized. Of this fact observant travellers cannot fail to have had occasional evidence. Sir Charles Lyell mentions one instance observed by him, which is specially104 interesting. “During a tour in Spain,” he says, “I was surprised to see a district of gently undulating378 ground in Catalonia, consisting of red and grey sandstone, and in some parts of red marl, almost entirely105 denuded106 of herbage, while the roots of the pines, holm oaks, and some other trees, were half exposed, as if the soil had been washed away by a flood. Such is the state of the forests, for example, between Oristo and Vich, and near San Lorenzo. But being overtaken by a violent thunderstorm, in the month of August, I saw the whole surface, even the highest levels of some flat-topped hills, streaming with mud, while on every declivity the devastation of torrents was terrific. The peculiarities107 in the physiognomy of the district were at once explained, and I was taught that, in speculating on the greater effects which the direct action of rain may once have produced on the surface of certain parts of England, we need not revert108 to periods when the heat of the climate was tropical.” He might have cited instances of such storms occurring in England. For example, White, in his delightful109 “Natural History of Selborne,” describes thus the effects of a storm which occurred on June 5, 1784: “At about a quarter after two the storm began in the parish of Harpley, moving slowly from north to south, and from thence it came over Norton Farm and so to Grange Farm, both in this parish. Had it been as extensive as it was violent (for it was very short) it must have ravaged110 all the neighbourhood. The extent of the storm was about two miles in length and one in breadth. There fell prodigious111 torrents of rain on the farms above mentioned, which occasioned a flood as violent as it was sudden, doing great damage to the meadows and fallows by deluging112 the one and washing away the soil of the other. The hollow lane towards Alton was so torn and disordered as not to be passable till mended, rocks being removed which weighed two hundredweight.”
We have mentioned the formation of dust, and the action of wind upon it, as a cause tending to level the surface of the land. It may appear to many that this cause is too insignificant to be noticed among those which modify the earth’s379 surface. In reality, however, owing to its continuous action, and to its always acting113 (in the main) in one direction, this cause is much more important than might be supposed. We overlook its action as actually going on around us, because in a few years, or in a few generations, it produces no change that can be readily noticed. But in long periods of time it changes very markedly the level of lower lands, and that too even in cities, where means exist for removing the accumulations of dust which are continually collecting on the surface of the earth. We know that the remains114 of old Roman roads, walls, houses, and so forth115, in this country, are found, not at the present level of the surface, but several feet—in some cases many yards—below this level. The same holds elsewhere, under the same conditions—that is, where we know quite certainly that the substances thus found underground were originally on the surface, and that there has been neither any disturbance116 causing them to be engulfed117, nor any deposition118 of scori?, volcanic119 dust, or other products of subterranean disturbance. We cannot hesitate to regard this burying of old buildings as due to the continual deposition of dust, which eventually becomes compacted into solid earth. We know, moreover, that the formation of dust is in the main due to rain converting the surface layers of the earth into mud, which on drying requires but the frictional action of heavy winds to rise in clouds of dust. In some soils this process goes on more rapidly than in others, as every one who has travelled much afoot is aware. There are parts of England, for instance, where, even in the driest summer, the daily deposition of dust on dry and breezy days is but slight, others where in such weather a dust layer at least a quarter of an inch in thickness is deposited in the course of a day. If we assumed, which would scarcely seem an exaggerated estimate, that in the course of a single year a layer of dust averaging an inch in thickness is deposited over the lower levels of the surface of the land, we should find that the average depth of the layer formed in the last thousand years would amount to no380 less than eighty-three feet. Of course in inhabited places the deposition of dust is checked, though not so much as most persons imagine. There is not probably in this country a single building five hundred years old, originally built at a moderately low level, the position of whose foundation does not attest the constant gathering120 of matter upon the surface. The actual amount by which the lower levels are raised and the higher levels diminished in the course of a thousand years may be very much less, but that it must amount to many feet can scarcely be questioned.
And as in considering the action of rain falling over a wide range of country, we have to distinguish between the slow but steady action of ordinary rains and the occasional violent action of great storms of rain, so in considering the effects of drought following after rain which has well saturated121 the land we have to distinguish between ordinarily dusty times and occasions when in a very short time, owing to the intensity122 of the heat and the violence of the wind large quantities of dust are spread over a wide area. Darwin thus describes the effect of such exceptional drought, as experienced in the years 1827–1832 in Buenos Ayres:—“So little rain fell that the vegetation, even to the thistles, failed; the brooks123 were dried up, and the whole country assumed the appearance of a dusty high road. This was especially the case in the northern part of the province of Buenos Ayres, and the southern part of Santa Fé.” He describes the loss of life caused by the want of water, and many remarkable circumstances of the drought which do not here specially concern us. He then goes on to speak of the dust which gathered over the open country. “Sir Woodbine Parish,” he says, “informed me of a very curious source of dispute. The ground being so long dry, such quantities of dust were blown about that in this open country the landmarks124 became obliterated125, and people could not tell the limits of their estates.” The dust thus scattered126 over the land, whether left or removed, necessarily formed part of the solid material brought from higher to lower levels, indirectly (in this case)381 through the action of rain; for a drought can only convert into friable127 matter earth which has before been thoroughly128 soaked. But the action of rain, which had originally led to the formation of these enormous masses of dust, presently took part in carrying the dust in the form of mud to yet lower levels. “Subsequently to the drought of 1827 to 1832,” proceeds Darwin, “a very rainy season followed, which caused great floods. Hence it is almost certain that some thousands of the skeletons” (of creatures whose deaths he had described before) “were buried by the deposits of the very next year. What could be the opinion of a geologist, viewing such an enormous collection of bones, of all kinds of animals and of all ages, thus embedded129 in one thick earthy mass? Would he not attribute it to a flood having swept over the surface of the land, rather than to the common order of things?” In fact, a single great drought, followed by a very rainy season, must in this instance, which was however altogether exceptional, have produced a layer or stratum such as geologists130 would ordinarily regard as the work of a much longer time and much more potent131 disturbing causes.
It may be well to consider in this place the question whether in reality the quantity of rain which falls now during our winter months does not greatly exceed that which formerly132 fell in that part of the year. The idea is very prevalent that our winters have changed entirely in character in recent times, and the fear (or the hope?) is entertained that the change may continue in the same direction until wet and mild winters replace altogether the cold which prevailed in former years. There is no sufficient reason, however, for supposing that any such change is taking place. It is, indeed, not difficult to find in the meteorological annals of the first half of the present century, instances of the occurrence of several successive winters very unlike the greater number of those which we have experienced during the last ten or twelve years. But if we take any considerable series of years in the last century we find the alternations of the382 weather very similar to those we at present recognize. Consider, for instance, Gilbert White’s brief summary of the weather from 1768 onwards:—
For the winter of 1768–69 we have October and the first part of November rainy; thence to the end of 1768 alternate rains and frosts; January and February frosty and rainy, with gleams of fine weather; to the middle of March, wind and rain.
For the winter of 1769–70 we have October frosty, the next fortnight rainy, the next dry and frosty. December windy, with rain and intervals133 of frost (the first fortnight very foggy); the first half of January frosty, thence to the end of February mild hazy134 weather. March frosty and brighter.
For 1770–71, from the middle of October to the end of the year, almost incessant135 rains; January severe frosts till the last week, the next fortnight rain and snow, and spring weather to the end of February. March frosty.
For 1771–72, October rainy, November frost with intervals of fog and rain, December bright mild weather with hoar frosts; then six weeks of frost and snow, followed by six of frost, sleet136, hail, and snow.
For 1772–73, October, November, and to December 22, rain, with mild weather; to the end of 1772, cold foggy weather; then a week of frost, followed by three of dark rainy weather. First fortnight of February frost; thence to the end of March misty137 showery weather.
Passing over the winter of 1773–74, which was half rainy, half frosty, what could more closely resemble the winter weather we have had so much of during the last few years, than that experienced in the winter of 1774–75? From August 24 to the third week of November, there was rain, with frequent intervals of sunny weather; to the end of December, dark dripping fogs; to the end of the first fortnight in March, rain almost every day.
And so on, with no remarkable changes, until the year 1792, the last of Gilbert White’s records.
383 If we limit our attention to any given month of winter, we find the same mixture of cold and dry with wet and open weather as we are familiar with at present. Take, for instance, the month usually the most wintry of all, viz., January. Passing over the years already considered, we have January, 1776, dark and frosty with much snow till the 26th (at this time the Thames was frozen over), then foggy with hoar frost; January, 1777, frosty till the 10th, then foggy and showery; 1778, frosty till the 13th, then rainy to the 24th, then hard frost; 1779, frost and showers throughout January; 1780, frost throughout; 1781, frost and snow to the 25th, then rain and snow; 1782, open and mild; 1783, rainy with heavy winds; 1784, hard frost; 1785, a thaw138 on the 2nd, then rainy weather to the 28th, the rest of the month frosty; 1786, frost and snow till January 7, then a week mild with much rain, the next week heavy snow, and the rest mild with frequent rain; 1787, first twenty-four days dark moist mild weather, then four days frost, the rest mild and showery; 1788, thirteen days mild and wet, five days of frost, and from January 18 to the end of the month dry windy weather; 1789, thirteen days hard frost, the rest of the month mild with showers; 1790, sixteen days of mild foggy weather with occasional rain, to the 21st frost, to the 28th dark with driving rains, and the rest mild dry weather; 1791, the whole of January mild with heavy rains; and lastly 1792, “some hard frost in January, but mostly wet and mild.”
There is nothing certainly in this record to suggest that any material change has taken place in our January weather during the last eight years. And if we had given the record of the entire winter for each of the years above dealt with the result would have been the same.
We have, in fact, very striking evidence in Gilbert White’s account of the cold weather of December, 1784, which he specially describes as “very extraordinary,” to show that neither our severe nor our average winter weather can differ materially from that which people experienced384 in the eighteenth century. “In the evening of December 9,” he says, “the air began to be so very sharp that we thought it would be curious to attend to the motions of a thermometer; we therefore hung out two, one made by Martin and one by Dolland” (sic, presumably Dollond), “which soon began to show us what we were to expect; for by ten o’clock they fell to twenty-one, and at eleven to four, when we went to bed. On the 10th, in the morning the quicksilver in Dolland’s glass was down to half a degree below zero, and that of Martin’s, which was absurdly graduated only to four degrees above zero, sank quite into the brass139 guard of the ball, so that when the weather became most interesting this was useless. On the 10th, at eleven at night, though the air was perfectly140 still, Dolland’s glass went down to one degree below zero!” The note of exclamation141 is White’s. He goes on to speak of “this strange severity of the weather,” which was not exceeded that winter, or at any time during the twenty-four years of White’s observations. Within the last quarter of a century, the thermometer, on more than one occasion, has shown two or three degrees below zero. Certainly the winters cannot be supposed to have been ordinarily severer than ours in the latter half of the last century, when we find that thermometers, by well-known instrument makers142, were so constructed as to indicate no lower temperature than four degrees above zero.
Let us return, after this somewhat long digression, to the levelling action of rain and rivers.
If we consider this action alone, we cannot but recognize in it a cause sufficient to effect the removal of all the higher parts of the land to low levels, and eventually of all the low-lying land to the sea, in the course of such periods as geology makes us acquainted with. The mud-banks at the mouths of rivers show only a part of what rain and river action is doing, yet consider how enormous is the mass which is thus carried into the sea. It has been calculated that in a single week the Ganges alone carries away from the385 soil of India and delivers into the sea twice as much solid substance as is contained in the great pyramid of Egypt. “The Irrawaddy,” says Sir J. Herschel, “sweeps off from Burmah 62 cubit feet of earth in every second of time on an average, and there are 86,400 seconds in every day, and 365 days in every year; and so on for other rivers. Nor is there any reason to fear or hope that the rains will cease, and this destructive process come to an end. For though the quantity of water on the surface of the earth is probably undergoing a slow process of diminution143, small portions of it year by year taking their place as waters under the earth,44 yet these processes are far too slow to appreciably144 affect the supply of water till a far longer period has elapsed than that during which (in all probability) life can continue upon the earth.
When we consider the force really represented by the downfall of rain, we need not greatly wonder that the386 levelling power of rain is so effective. The sun’s heat is the true agent in thus levelling the earth, and if we regard, as we justly may, the action of water, whether in the form of rain or river, or of sea-wave raised by wind or tide, as the chief levelling and therefore destructive force at work upon the earth, and the action of the earth’s vulcanian energies as the chief restorative agent, then we may fairly consider the contest as lying between the sun’s heat and the earth’s internal heat. There can be little question as to what would be the ultimate issue of the contest if land and sea and air all endured or were only so far modified as they were affected by these causes. Sun-heat would inevitably145 prevail in the long run over earth-heat. But we see from the condition of our moon how the withdrawal146 of water and air from the scene must diminish the sun’s power of levelling the irregularities of the earth’s surface. We say advisedly diminish, not destroy; for there can be no question that the solar heat alternating with the cold of the long lunar night is still at work levelling, however slowly, the moon’s surface; and the same will be the case with our earth when her oceans and atmosphere have disappeared by slow processes of absorption.
The power actually at work at present in producing rain, and so, indirectly, in levelling the earth’s surface, is enormous. I have shown that the amount of heat required to evaporate a quantity of water which would cover an area of 100 square miles to a depth of one inch would be equal to the heat which would be produced by the combustion147 of half a million tons of coals, and that the amount of force of which this consumption of heat would be the equivalent corresponds to that which would be required to raise a weight of upwards148 of one thousand millions of tons to a height of one mile.45 When we remember that the land surface of the earth amounts to about fifty millions of square miles, we perceive how enormous must be the force-equivalent of the annual rainfall of our earth. We are apt to387 overlook when contemplating149 the silent and seemingly quiet processes of nature—such as the formation of the rain-cloud or the precipitation of rain—the tremendous energy of the forces really causing these processes. “I have seen,” says Professor Tyndall, “the wild stone-avalanches of the Alps, which smoke and thunder down the declivities with a vehemence150 almost sufficient to stun151 the observer. I have also seen snow-flakes descending so softly as not to hurt the fragile spangles of which they were composed; yet to produce from aqueous vapour a quantity which a child could carry of that tender material demands an exertion152 of energy competent to gather up the shattered blocks of the largest stone-avalanche I have ever seen, and pitch them to twice the height from which they fell.”
点击
收听单词发音
收听单词发音 |
1
remodelling
|
|
| v.改变…的结构[形状]( remodel的现在分词 ) | |
参考例句： |
|
|
|
|
2
preservative
|
|
| n.防腐剂；防腐料；保护料；预防药 | |
参考例句： |
|
|
|
|
3
igneous
|
|
| adj.火的，火绒的 | |
参考例句： |
|
|
|
|
4
upheaval
|
|
| n.胀起，(地壳)的隆起；剧变，动乱 | |
参考例句： |
|
|
|
|
5
essentially
|
|
| adv.本质上，实质上，基本上 | |
参考例句： |
|
|
|
|
6
dwellers
|
|
| n.居民，居住者( dweller的名词复数 ) | |
参考例句： |
|
|
|
|
7
annually
|
|
| adv.一年一次，每年 | |
参考例句： |
|
|
|
|
8
bowels
|
|
| n.肠，内脏，内部；肠( bowel的名词复数 )；内部，最深处 | |
参考例句： |
|
|
|
|
9
geologist
|
|
| n.地质学家 | |
参考例句： |
|
|
|
|
10
disintegration
|
|
| n.分散，解体 | |
参考例句： |
|
|
|
|
11
strata
|
|
| n.地层（复数）；社会阶层 | |
参考例句： |
|
|
|
|
12
torrent
|
|
| n.激流，洪流；爆发，(话语等的)连发 | |
参考例句： |
|
|
|
|
13
withdrawn
|
|
| vt.收回；使退出；vi.撤退，退出 | |
参考例句： |
|
|
|
|
14
drawn
|
|
| v.拖，拉，拔出；adj.憔悴的，紧张的 | |
参考例句： |
|
|
|
|
15
drenched
|
|
| adj.湿透的；充满的v.使湿透( drench的过去式和过去分词 )；在某人（某物）上大量使用（某液体） | |
参考例句： |
|
|
|
|
16
crumbles
|
|
| 酥皮水果甜点( crumble的名词复数 ) | |
参考例句： |
|
|
|
|
17
remarkable
|
|
| adj.显著的，异常的，非凡的，值得注意的 | |
参考例句： |
|
|
|
|
18
catastrophe
|
|
| n.大灾难，大祸 | |
参考例句： |
|
|
|
|
19
catastrophes
|
|
| n.灾祸( catastrophe的名词复数 )；灾难；不幸事件；困难 | |
参考例句： |
|
|
|
|
20
attain
|
|
| vt.达到，获得，完成 | |
参考例句： |
|
|
|
|
21
phenomena
|
|
| n.现象 | |
参考例句： |
|
|
|
|
22
inundated
|
|
| v.淹没( inundate的过去式和过去分词 )；（洪水般地）涌来；充满；给予或交予（太多事物）使难以应付 | |
参考例句： |
|
|
|
|
23
outlet
|
|
| n.出口/路；销路；批发商店；通风口；发泄 | |
参考例句： |
|
|
|
|
24
avalanche
|
|
| n.雪崩，大量涌来 | |
参考例句： |
|
|
|
|
25
avalanches
|
|
| n.雪崩( avalanche的名词复数 ) | |
参考例句： |
|
|
|
|
26
glacier
|
|
| n.冰川，冰河 | |
参考例句： |
|
|
|
|
27
gall
|
|
| v.使烦恼，使焦躁，难堪；n.磨难 | |
参考例句： |
|
|
|
|
28
considerably
|
|
| adv.极大地；相当大地；在很大程度上 | |
参考例句： |
|
|
|
|
29
imprisoned
|
|
| 下狱，监禁( imprison的过去式和过去分词 ) | |
参考例句： |
|
|
|
|
30
gorges
|
|
| n.山峡，峡谷( gorge的名词复数 )；咽喉v.（用食物把自己）塞饱，填饱( gorge的第三人称单数 )；作呕 | |
参考例句： |
|
|
|
|
31
sweeping
|
|
| adj.范围广大的，一扫无遗的 | |
参考例句： |
|
|
|
|
32
granite
|
|
| adj.花岗岩，花岗石 | |
参考例句： |
|
|
|
|
33
circumference
|
|
| n.圆周，周长，圆周线 | |
参考例句： |
|
|
|
|
34
overthrown
|
|
| adj. 打翻的，推倒的，倾覆的 动词overthrow的过去分词 | |
参考例句： |
|
|
|
|
35
noted
|
|
| adj.著名的，知名的 | |
参考例句： |
|
|
|
|
36
ERECTED
|
|
| adj. 直立的，竖立的，笔直的 vt. 使 ... 直立，建立 | |
参考例句： |
|
|
|
|
37
standing
|
|
| n.持续，地位；adj.永久的，不动的，直立的，不流动的 | |
参考例句： |
|
|
|
|
38
vertical
|
|
| adj.垂直的，顶点的，纵向的；n.垂直物，垂直的位置 | |
参考例句： |
|
|
|
|
39
worthy
|
|
| adj.(of)值得的，配得上的；有价值的 | |
参考例句： |
|
|
|
|
40
waggons
|
|
| 四轮的运货马车( waggon的名词复数 )； 铁路货车； 小手推车 | |
参考例句： |
|
|
|
|
41
attest
|
|
| vt.证明，证实；表明 | |
参考例句： |
|
|
|
|
42
attested
|
|
| adj.经检验证明无病的，经检验证明无菌的v.证明( attest的过去式和过去分词 )；证实；声称…属实；使宣誓 | |
参考例句： |
|
|
|
|
43
steadily
|
|
| adv.稳定地；不变地；持续地 | |
参考例句： |
|
|
|
|
44
obliteration
|
|
| n.涂去，删除；管腔闭合 | |
参考例句： |
|
|
|
|
45
previously
|
|
| adv.以前，先前（地） | |
参考例句： |
|
|
|
|
46
copious
|
|
| adj.丰富的，大量的 | |
参考例句： |
|
|
|
|
47
pier
|
|
| n.码头；桥墩，桥柱；[建]窗间壁，支柱 | |
参考例句： |
|
|
|
|
48
masonry
|
|
| n.砖土建筑；砖石 | |
参考例句： |
|
|
|
|
49
premises
|
|
| n.建筑物，房屋 | |
参考例句： |
|
|
|
|
50
abruptly
|
|
| adv.突然地，出其不意地 | |
参考例句： |
|
|
|
|
51
extremity
|
|
| n.末端，尽头；尽力；终极；极度 | |
参考例句： |
|
|
|
|
52
momentum
|
|
| n.动力，冲力，势头；动量 | |
参考例句： |
|
|
|
|
53
ascent
|
|
| n.(声望或地位)提高；上升，升高；登高 | |
参考例句： |
|
|
|
|
54
swollen
|
|
| adj.肿大的，水涨的；v.使变大，肿胀 | |
参考例句： |
|
|
|
|
55
declivity
|
|
| n.下坡，倾斜面 | |
参考例句： |
|
|
|
|
56
watershed
|
|
| n.转折点，分水岭，分界线 | |
参考例句： |
|
|
|
|
57
gravel
|
|
| n.砂跞；砂砾层；结石 | |
参考例句： |
|
|
|
|
58
rivulet
|
|
| n.小溪，小河 | |
参考例句： |
|
|
|
|
59
dealing
|
|
| n.经商方法，待人态度 | |
参考例句： |
|
|
|
|
60
mere
|
|
| adj.纯粹的；仅仅，只不过 | |
参考例句： |
|
|
|
|
61
velocity
|
|
| n.速度，速率 | |
参考例句： |
|
|
|
|
62
inadequate
|
|
| adj.(for,to)不充足的，不适当的 | |
参考例句： |
|
|
|
|
63
overflowing
|
|
| n. 溢出物,溢流 adj. 充沛的，充满的 动词overflow的现在分词形式 | |
参考例句： |
|
|
|
|
64
depressed
|
|
| adj.沮丧的，抑郁的，不景气的，萧条的 | |
参考例句： |
|
|
|
|
65
indirectly
|
|
| adv.间接地，不直接了当地 | |
参考例句： |
|
|
|
|
66
beacon
|
|
| n.烽火，（警告用的）闪火灯，灯塔 | |
参考例句： |
|
|
|
|
67
subterranean
|
|
| adj.地下的，地表下的 | |
参考例句： |
|
|
|
|
68
precipitated
|
|
| v.（突如其来地）使发生( precipitate的过去式和过去分词 )；促成；猛然摔下；使沉淀 | |
参考例句： |
|
|
|
|
69
deluges
|
|
| v.使淹没( deluge的第三人称单数 )；淹没；被洪水般涌来的事物所淹没；穷于应付 | |
参考例句： |
|
|
|
|
|
70
abridged
|
|
| 削减的，删节的 | |
参考例句： |
|
|
|
|
71
descending
|
|
| n. 下行 adj. 下降的 | |
参考例句： |
|
|
|
|
72
promiscuous
|
|
| adj.杂乱的，随便的 | |
参考例句： |
|
|
|
|
73
frightful
|
|
| adj.可怕的；讨厌的 | |
参考例句： |
|
|
|
|
74
shrubs
|
|
| 灌木( shrub的名词复数 ) | |
参考例句： |
|
|
|
|
75
devastated
|
|
| v.彻底破坏( devastate的过去式和过去分词)；摧毁；毁灭；在感情上（精神上、财务上等）压垮adj.毁坏的；极为震惊的 | |
参考例句： |
|
|
|
|
76
interval
|
|
| n.间隔，间距；幕间休息，中场休息 | |
参考例句： |
|
|
|
|
77
chasms
|
|
| 裂缝( chasm的名词复数 )； 裂口； 分歧； 差别 | |
参考例句： |
|
|
|
|
78
excavations
|
|
| n.挖掘( excavation的名词复数 )；开凿；开凿的洞穴（或山路等）；（发掘出来的）古迹 | |
参考例句： |
|
|
|
|
79
prostrated
|
|
| v.使俯伏，使拜倒( prostrate的过去式和过去分词 )；（指疾病、天气等）使某人无能为力 | |
参考例句： |
|
|
|
|
80
tributary
|
|
| n.支流；纳贡国；adj.附庸的；辅助的；支流的 | |
参考例句： |
|
|
|
|
81
excavated
|
|
| v.挖掘( excavate的过去式和过去分词 )；开凿；挖出；发掘 | |
参考例句： |
|
|
|
|
82
densely
|
|
| ad.密集地；浓厚地 | |
参考例句： |
|
|
|
|
83
cataclysm
|
|
| n.洪水，剧变，大灾难 | |
参考例句： |
|
|
|
|
84
devastation
|
|
| n.毁坏；荒废；极度震惊或悲伤 | |
参考例句： |
|
|
|
|
85
boulders
|
|
| n.卵石( boulder的名词复数 )；巨砾；（受水或天气侵蚀而成的）巨石；漂砾 | |
参考例句： |
|
|
|
|
86
picturesque
|
|
| adj.美丽如画的，（语言）生动的，绘声绘色的 | |
参考例句： |
|
|
|
|
87
insignificant
|
|
| adj.无关紧要的，可忽略的，无意义的 | |
参考例句： |
|
|
|
|
88
mighty
|
|
| adj.强有力的；巨大的 | |
参考例句： |
|
|
|
|
89
naturalist
|
|
| n.博物学家(尤指直接观察动植物者) | |
参考例句： |
|
|
|
|
90
artillery
|
|
| n.(军)火炮，大炮；炮兵(部队) | |
参考例句： |
|
|
|
|
91
agitated
|
|
| adj.被鼓动的，不安的 | |
参考例句： |
|
|
|
|
92
vessel
|
|
| n.船舶；容器，器皿；管，导管，血管 | |
参考例句： |
|
|
|
|
93
colossal
|
|
| adj.异常的，庞大的 | |
参考例句： |
|
|
|
|
94
concussion
|
|
| n.脑震荡；震动 | |
参考例句： |
|
|
|
|
95
prospect
|
|
| n.前景，前途；景色，视野 | |
参考例句： |
|
|
|
|
96
glided
|
|
| v.滑动( glide的过去式和过去分词 )；掠过；（鸟或飞机 ） 滑翔 | |
参考例句： |
|
|
|
|
97
glaciers
|
|
| 冰河，冰川( glacier的名词复数 ) | |
参考例句： |
|
|
|
|
98
derive
|
|
| v.取得；导出；引申；来自；源自；出自 | |
参考例句： |
|
|
|
|
99
derived
|
|
| vi.起源；由来；衍生；导出v.得到( derive的过去式和过去分词 )；（从…中）得到获得；源于；（从…中）提取 | |
参考例句： |
|
|
|
|
100
affected
|
|
| adj.不自然的，假装的 | |
参考例句： |
|
|
|
|
101
tracts
|
|
| 大片土地( tract的名词复数 )； 地带； （体内的）道； （尤指宣扬宗教、伦理或政治的）短文 | |
参考例句： |
|
|
|
|
102
torrents
|
|
| n.倾注；奔流( torrent的名词复数 )；急流；爆发；连续不断 | |
参考例句： |
|
|
|
|
103
stratum
|
|
| n.地层，社会阶层 | |
参考例句： |
|
|
|
|
104
specially
|
|
| adv.特定地；特殊地；明确地 | |
参考例句： |
|
|
|
|
105
entirely
|
|
| ad.全部地，完整地；完全地，彻底地 | |
参考例句： |
|
|
|
|
106
denuded
|
|
| adj.[医]变光的，裸露的v.使赤裸( denude的过去式和过去分词 )；剥光覆盖物 | |
参考例句： |
|
|
|
|
107
peculiarities
|
|
| n. 特质, 特性, 怪癖, 古怪 | |
参考例句： |
|
|
|
|
108
revert
|
|
| v.恢复，复归，回到 | |
参考例句： |
|
|
|
|
109
delightful
|
|
| adj.令人高兴的，使人快乐的 | |
参考例句： |
|
|
|
|
110
ravaged
|
|
| 毁坏( ravage的过去式和过去分词 )； 蹂躏； 劫掠； 抢劫 | |
参考例句： |
|
|
|
|
111
prodigious
|
|
| adj.惊人的，奇妙的；异常的；巨大的；庞大的 | |
参考例句： |
|
|
|
|
112
deluging
|
|
| v.使淹没( deluge的现在分词 )；淹没；被洪水般涌来的事物所淹没；穷于应付 | |
参考例句： |
|
|
|
|
113
acting
|
|
| n.演戏，行为，假装；adj.代理的，临时的，演出用的 | |
参考例句： |
|
|
|
|
114
remains
|
|
| n.剩余物，残留物；遗体，遗迹 | |
参考例句： |
|
|
|
|
115
forth
|
|
| adv.向前；向外，往外 | |
参考例句： |
|
|
|
|
116
disturbance
|
|
| n.动乱，骚动；打扰，干扰；(身心)失调 | |
参考例句： |
|
|
|
|
117
engulfed
|
|
| v.吞没，包住( engulf的过去式和过去分词 ) | |
参考例句： |
|
|
|
|
118
deposition
|
|
| n.免职，罢官；作证；沉淀；沉淀物 | |
参考例句： |
|
|
|
|
119
volcanic
|
|
| adj.火山的；象火山的；由火山引起的 | |
参考例句： |
|
|
|
|
120
gathering
|
|
| n.集会，聚会，聚集 | |
参考例句： |
|
|
|
|
121
saturated
|
|
| a.饱和的，充满的 | |
参考例句： |
|
|
|
|
122
intensity
|
|
| n.强烈，剧烈；强度；烈度 | |
参考例句： |
|
|
|
|
123
brooks
|
|
| n.小溪( brook的名词复数 ) | |
参考例句： |
|
|
|
|
124
landmarks
|
|
| n.陆标( landmark的名词复数 )；目标；（标志重要阶段的）里程碑 ~ (in sth)；有历史意义的建筑物（或遗址） | |
参考例句： |
|
|
|
|
125
obliterated
|
|
| v.除去( obliterate的过去式和过去分词 )；涂去；擦掉；彻底破坏或毁灭 | |
参考例句： |
|
|
|
|
126
scattered
|
|
| adj.分散的，稀疏的；散步的；疏疏落落的 | |
参考例句： |
|
|
|
|
127
friable
|
|
| adj.易碎的 | |
参考例句： |
|
|
|
|
128
thoroughly
|
|
| adv.完全地，彻底地，十足地 | |
参考例句： |
|
|
|
|
129
embedded
|
|
| a.扎牢的 | |
参考例句： |
|
|
|
|
130
geologists
|
|
| 地质学家，地质学者( geologist的名词复数 ) | |
参考例句： |
|
|
|
|
131
potent
|
|
| adj.强有力的，有权势的；有效力的 | |
参考例句： |
|
|
|
|
132
formerly
|
|
| adv.从前，以前 | |
参考例句： |
|
|
|
|
133
intervals
|
|
| n.[军事]间隔( interval的名词复数 )；间隔时间；[数学]区间；（戏剧、电影或音乐会的）幕间休息 | |
参考例句： |
|
|
|
|
134
hazy
|
|
| adj.有薄雾的，朦胧的；不肯定的，模糊的 | |
参考例句： |
|
|
|
|
135
incessant
|
|
| adj.不停的，连续的 | |
参考例句： |
|
|
|
|
136
sleet
|
|
| n.雨雪；v.下雨雪，下冰雹 | |
参考例句： |
|
|
|
|
137
misty
|
|
| adj.雾蒙蒙的，有雾的 | |
参考例句： |
|
|
|
|
138
thaw
|
|
| v.（使）融化，（使）变得友善；n.融化，缓和 | |
参考例句： |
|
|
|
|
139
brass
|
|
| n.黄铜；黄铜器，铜管乐器 | |
参考例句： |
|
|
|
|
140
perfectly
|
|
| adv.完美地，无可非议地，彻底地 | |
参考例句： |
|
|
|
|
141
exclamation
|
|
| n.感叹号，惊呼，惊叹词 | |
参考例句： |
|
|
|
|
142
makers
|
|
| n.制造者，制造商（maker的复数形式） | |
参考例句： |
|
|
|
|
143
diminution
|
|
| n.减少；变小 | |
参考例句： |
|
|
|
|
144
appreciably
|
|
| adv.相当大地 | |
参考例句： |
|
|
|
|
145
inevitably
|
|
| adv.不可避免地；必然发生地 | |
参考例句： |
|
|
|
|
146
withdrawal
|
|
| n.取回，提款；撤退，撤军；收回，撤销 | |
参考例句： |
|
|
|
|
147
combustion
|
|
| n.燃烧；氧化；骚动 | |
参考例句： |
|
|
|
|
148
upwards
|
|
| adv.向上，在更高处...以上 | |
参考例句： |
|
|
|
|
149
contemplating
|
|
| 深思，细想，仔细考虑( contemplate的现在分词 )； 注视，凝视； 考虑接受（发生某事的可能性）； 深思熟虑，沉思，苦思冥想 | |
参考例句： |
|
|
|
|
150
vehemence
|
|
| n.热切；激烈；愤怒 | |
参考例句： |
|
|
|
|
151
stun
|
|
| vt.打昏，使昏迷，使震惊，使惊叹 | |
参考例句： |
|
|
|
|
152
exertion
|
|
| n.尽力，努力 | |
参考例句： |
|
|
|
| 欢迎访问英文小说网 |