Outlines of the Earth's History: A Popular Study in Physiography

s and th

he consequences arising from the applications of energy to the outer part of the planet have been attended to, but the main aim has been to set forth the work which solar energy, operating i

ected by gravitation. In the form of steam, water which has been built into rocks and volcanically expelled by tensions, due to the heat which it has acquired at great depths below the surface, blows forth great quantities of lava, which is contributed to the formation of strata, either directly in the solid form or indirectly, after having been dissolved in the sea. Acting as waves, water impelled by solar energy transmitted to it by the winds beats against the shores, wear

ormed in what are called dead seas, in which case the detrital materials are commonly small in amount, for the reason that the inflowing streams are inconsiderable; in such basins there is normally a large share of saline materials, which are laid down by the evaporation of the water. In ordinary lakes the deposits which are formed are mostly due to the sediment that the rivers import. These materials are usually fine-grained, and the sand or

le height above the sea level, where the erosive agents may readily attack them. In consequence of this condition, lacustrine beds are rarely found of great antiquity; they generally disappear

only the region where the greater part of the sedimentation is effected, but that in which the work assumes the greatest variety. The sea bottoms, as regards the deposits formed upon them, are naturally divided into two regions-the one in which the

large river which bears a great tide of sediment to the sea, the land waste may not affect the bottom for more than a mile or two from the shore. Where these conditions are reversed, the débris from the air-covered region may be found three or four hundred miles from the coast line. It should also be noted that

s from the action of the waves, the deposits formed from the shore outwardly will consist of coarse materials, such as pebbles near the coast, of sand in the deeper and remoter section, and of finer silt in the part of the deposit which is farthest out. With each change in the level of the coast line the position of these belts will necessarily be altered. Where a great river enter

t of animals and plants, commonly develops in a very luxuriant way. Only where the bottom is composed of drifting sands, which do not afford a foothold for those species which need to rest upon the shore, do we fail to find that surface thickly tenanted with varied forms. These are arranged according to the depth of the bottom. The species of marine plants which are attached to fixed objects are limited t

adjustment of the conditions which favour the growth of certain creatures; very slight geographic changes, by inducing movements of sand or mud, are apt to interrupt their formation, bringing about a great and immediate alteration in the character of the deposits. Thus it is that where geologists find considerable fields of rock, where limestones are intercalated with sandstones and deposits of clay, they are justified in assuming that the strata were laid down near some ancient shore.

tains the bottom of the sea. By far the larger part of the contributions which go to the formation of these deep-sea strata come from organic remains, which are continually falling upon the sea floor. In part, this waste is derived fr

e fossilization of any form depends upon the accumulation of sediment before the processes of destruction have overtaken them, and among these processes we must give the first place to the creatures which subsist on shells, bones, or other substances of like nature which find their way to the ocean floor. In the absolute darkness, the still water, and the exceeding cold of the deeper seas, animals find difficult conditions for development. Moreover, in this deep realm there is no native vegetation, and, in

o digesting the débris which gathers on the sea bottom. Wandering over this surface, much in the manner of our ordinary earthworms, these creatures devour the mud, voiding the matter from their bodies in a yet more perfectly divided form. Hence it comes about that the limestone beds, so commonly formed beneath the open seas, are generally composed of mat

s with care, we observe that on the upper surface on the limestone the remains of the animal which dwelt on the ancient sea floor are remarkably well preserved, they having evidently escaped the effect of the process which reduced their ancestors, whose remains constitute the layer, to mud. Furthermore, we note that the shaly layer is not only lacking in lime, but commonly contains no trace of animals such as might have dwelt on the bottom. The fossils it bears are usually of species which swam in the o

the run of ocean currents. It seems to the writer, however, that while these divisions may in certain cases be due to the above-mentioned and, indeed, to a great variety of causes, they are in general best to be explained by the action of earthquakes. Water being an exceedingly elastic substance, an earthquake passes through it with much g

ich dwell upon the bottom, are provided with an array of contrivances which enable them to clear away from their bodies such small quantities of silt as may inconvenience them. Thus, in the case of our common clam, the breathing organs are covered with vibratory cilia, which, acting like brooms, sweep off any foreign matter which may come upon their surfaces. Moreover, the creature has a long, double, spoutlike organ, which it can elevate some distance above the bottom, through which it draws and discharges the water from which it obtains food and air. Other forms, such as the crinoids, or sea lilies, elevate the breathing parts on top

been able to find where they disappeared. This fact makes it clear that the destruction which took place at the stage where these partings were formed was widespread; so far as it was due to earthquake shocks, we may fairly believe that

here the sea is deep, the effect of this wave on the bottom may be but slight; but as the undulation attains shallower water, and in proportion to the shoaling, the front of the surge is retarded in its advance by the friction of the bottom, while the rear part, being in deeper water, crowds upon the advancing line. The action is precisely that which has been described as occurring in wind-made waves as they approac

welt upon the bottom, but from those which inhabited the higher-lying waters. If, now, we take a portion of the limestone layer which lies above or below the shale parting, and carefully dissolve out with acids the limy matter which it contains, we obtain a residuum which in general character, except so far as the particles may have been affected by the acid, is exactly like the material which forms the claylike partition. We are thus readily led to the conclusion that on the floors of the deeper seas there is constantly descending, in the form of a very slow shower, a mas

states of lava in which the material, because of the vesicles which it contains, can float for ages before it comes to rest on the sea bottom. Variations in the volcanic waste contributed to the sea floor may somewhat affect the quantity of the inorganic sediments, but, as a whole, the downfalling of these fragments is probably at a singularly uniform rate. It is otherwise with the contributions of sediment arising from organic forms. This varie

mass of limy matter, which is forming very massive limestone strata, somewhat resembling chalk deposits, such as abundantly occur in Great Britain, in the neighbouring parts of Europe, in Texas, and elsewhere. Accumulations such as this, where the supply is derived from the surface of the water, are not affected by the accidents whi

r are to a great extent affected by the materials which these vents cast forth. Lava streams and showers represent only a part of the contributions from volcanoes, which finally find their way to the bottom. In larger part, the materials thrown forth are probably first dissolved in the wa

ssolve lime rocks in acids. This process of solution, by which the limy matter deposited on the bottom is taken back into the water, goes on everywhere, but at a rate which increases with the depth. This increase is due in part to the augmentation of pressure, and in part to the larger share of carbonic dioxide which the water at great depths holds. The result is, that explorations with the dredge seem to indicate that on certain parts of

ical store of the sea water can not be directly taken into the structures of animals; it can only be immediately appropriated by the marine plants. These forms can only develop in that superficial realm of the seas which is penetrated by the sunlight, or say within the depth of five hundred feet, mostly within one hundred feet of the surface, about one thirtieth of the average, and about one fiftieth of the maximum ocean depth. On this marine plant life, and in a small measure on the vegetable matter derived from the land, the marine animals primarily depend for their provender. Through the conditions which bring about the formation of Sargassum

h day for the distance of about two hundred and fifty feet. In the shallower water this motion increases in proportion to the shoaling, and in the regions near the shores the currents of the sea which, except the massive drift from the poles, do not usually touch the bottom, begin to have their influence. Where the water is less than a hundred feet in depth, each wave contributes to the movement, which attains its maximum near the shore, where every surge sweeps the water rapidly to and fro. It is in this surge belt, where the waves are broken, that marine animals are best provided with food, and it is here that their growth is most rapid. If the student will obtain a pint of water from the

e shore belt is due to the fact that the waters are there subjected to a constant proce

onical shell, which faces the water with a domelike outside, and which at the moment of the stroke is drawn down upon the rock by the strong muscle which fastens the creature to its foundation. The barnacles, which with their wedge-shaped prows cut the water at the moment of the stroke, but open in the pauses between the waves

by brought into a realm of greater warmth, or perhaps when penetrated by dikes and thereby heated, these changes go yet further. More of the material is commonly rearranged by solution and redeposition, so that limestone may be converted into crystalline marble, granular sandstones into firm masses, known as quartzites, and clays into the harder form of slate. Where the changes go to the extreme point, rocks originally distinctly bedded probably may be so taken to pieces and made over that all traces of their stratification may be destroyed, all fossils obliterated, and the stone transformed into mica schist, or granite or other crystalline rock. It may be injected into the overlying strata in the form of dikes, or it may be blown forth into the air thr

hqua

s. Even when matter is built into the solid rock, it is doubtful whether any grain of it ever comes really to rest. Under the strains which arise from the contraction of the earth's interior and the chemical changes which the rocks undergo, each bit is subject to ever-changing thrusts, which somewhat affect its position. If we in any way

particles, after their vibratory movement, return to their original place. For purposes of illustration the first, or translatory motion, may be compared to that which takes place when a bell is carried along upon a locomotive or a shi

thrown upon a brick floor, the rebound will be very much diminished. It is well to consider what happens to produce the rebound. When the sphere strikes the floor it changes its shape, becoming shorter in the axis at right angles to the point which was struck, and at the same instant expanded along the equator of that axis. The flattening remains for only a small fraction of a second; the sphere vibrates so that it stretches along the line on which it previously shortened, and, as this movement takes place with great swif

ommonest cause of the jarrings in the earth is found in the formation of fractures, known as faults. If the reader has ever been upon a frozen lake at a time when the weather was growing colder, and the ice, therefore, was shrinking, he may have noted the rending sound and the slight vibration which comes with the formation of a crack traversing the sheet of ice. At such a time he feels a movement which is an earthquake, and wh

e fault fissures are often at the moment of their formation filled by a violent inrush of liquid rock. This, as it swiftly moves along, tears away masses from the walls, and when it strikes the end of the opening delivers a blow which may be of great violence. The nature of this stroke may be judged by the familiar instance where the relatively slow-flowing stream from a hydrant pipe is suddenly choked by closing the stopcock. Unless the plumber provides a cushion of air to diminish the energy of the blow, it is often strong e

e great earthquake of 1755, known as the Lisbon shock, the records make it seem probable that the movement was felt over one eighth part of the earth's surface. Such great disturbances probably bring about a motion of the rocks near the point of origin, which may be expressed in oscillations having an

his wave are at right angles to the seat of the originating disturbance, so that the shock may come to the surface in a line forming any angle between the vertical and the nearly horizontal. Where, as in a volcanic eruption, the s

regular. Moving through materials of one density, and with a rate of vibration determined by those conditions, the impulse is with difficulty communicated to strata which naturally vibrate at another speed. In many cases, as where a shock passing through dense crystalline strata encounters a mass of soft sandstone, the wave, in place of going on,

akes impress on the under earth is mainly due to the fact that in almost every part of the crust tensions or strains of other kinds are continually forming. These may for ages prove without effect until the earth is jarred, when motions will suddenly take place which in a moment may alter the conditions of the rocks throughout a wide field. In a word, a great earthquake caused by the formation of an extensive fault is likely to produce any number of slight dislocations, each of which is in turn shock-making, sending its little wave to complicate the great oscillation. Nor does the perturbing effect of these jarring movements cease with the fractures which they set

. In a similar way the frozen earth breaks open, sometimes with a shock which is often counted as an earthquake. Again, the ashes in a sifter or the gravel on a sieve show how each shaking may relieve certain tensions established by gravity, while they create others which are in turn to be re

eads to their downfall, but where they may remain long suspended, provided they are not disturbed. Thus, wherever there are high and steep cliffs, great falls of rock are likely to occur when the earthquake movements traverse the under earth. In more than one instance observers, so placed that they commanded a view of distant mountains, have noticed the downfall of precipices in the path of the shock before the trembl

that the soil and the forests which stood on it were precipitated into the river beds, so that many tree-clad summits became fields of bare rock. The effect of this action is immensely to increase the amount of detritus which the streams convey to the sea. After the great J

egrees, which in an unshaken region would be thickly soil-covered, are deprived of the coating by the downward movement of the waste which the disturbances bring about. A familiar example of this action may be had by watching the workmen engaged in sifting sand, by casting t

rn movement, which occurs the instant thereafter. The consequences of this action are often singular, and in cases constitute the most frightful elements of a shock which the sufferer beholds. In the great earthquake of 1811, which ravaged the section of the Mississippi Valley between the mouth of the Ohio and Vicksburg, these crevices were so numerously formed that the pioneers protected themselves from the danger of being caught in their jaws by felling trees so that th

trata which it traverses. In certain cases two faults conjoin their action, so that a portion of the surface disappears beneath the earth, entombing whatever may have stood on the vanished site. Thus in the great shock known as that of Lisbon, which occurred in 1755, the stone quay along the harbour, where many thousand people had sought refuge from the falling buildings of the city, suddenly sank down w

aulting. Fig. A shows the original position; B, the position after faulting; b

plentifully goes on wherever the rocks are still in an uncemented state. The result is often the production of changes which lead to the expulsion of gases. Thus, in the Charleston earthquake of 1883, the surface over an area of many hundred square miles was pitted with small craters, formed by the uprush of water impelled by its contained gases. These little water volcanoes-for such we may call them-sometimes occur to the number of a dozen or more on each acre of ground in the violently shaken district. They indicate one result of the physical and chemical alterations which earthquake shocks bring a

forward part. The result is, that the surge mounts ever higher and higher as it draws near the shore, upon which it may roll as a vast wave having the height of fifty feet or more and a width quite unparalleled by any wave produced from wind action. Waves of this description are most common in the Pacific Ocean. Although but occasional, the damage which they may inflict is very great. As the movement approaches the shore, vessels, however well anchored, are dragged away to seaward by the great back lash of the wave, a phenomenon which may be perceived even in th

r otherwise badly shaken by a sudden blow received in the midst of a quiet sea. The impression commonly conveyed to the sailors is that the craft has struck upon a rock. The explanation is that an earthquake jar, in traversing the water, has delivered its blow to the ship. As the speed of this jarring movement is very mu

est earthquake shock the earth moves not once to and fro, but very many times. In a considerable shock the successive diminishing swingings amount to dozens before they become so slight as to elude perception. Although the first swaying is the strongest, and generally the most destructive, the quick to-and-fro motions are apt to continue and to complete the devastation which the first brings about. The vibrations due to any one shock take place with great rapidity

-walled cliffs and steep slopes of earth, break down under the assaults. It is therefore no matter of surprise that the buildings which man erects, where they are composed of masonry, suffer greatly from these tremblings. In almost all cases human

lf experiences in the movement. A building of any height with its walls unsupported by neighbouring structures may find its roof rocked to and fro through an arc which has a length of feet, while its base moves only through a length of inches. The reader may see an example of this nature if h

cular that they give way and are carried down by the weight which they bore. It has often been remarked in earthquake shocks that tall columns, even where composed of many blocks, survive a shock which overturns lower buildings where thin walls support several floors, on each of which is accumulated a considerable amount of weight. In the case of the column, the strains are even, and the whole structure may rock to and fro without toppling over. As

tions, and all the parts of the walls which are not supported by strong masonry continuous from top to bottom are broken to pieces. In such cases it has been remarked that the bodies of men are often thrown considerable distances. It is asserted, indeed, that in the Riobamba shock they were cast upward to the

in that part of the field where the motion is, as regards its direction, between the vertical and the horizontal-a position in which the edifice is likely to receive at once the destructive effect arising from the sharp upward thrust of the vertical movement and the oscillating action of that which is in a horizontal direction. Against strains of this description, where the movements have an amplitude of more than a few inches, no ordinary masonry edifice can be made perfectl

le lands of northern Europe, never gained a firm foothold in those regions about the Mediterranean which are frequently visited by severe convulsions of the earth. There the Grecian or the Romanesque styles, which are of a much more massive type, retain their places and are the fashions to the present day. Even this manner of building, though affording a certain security against slight tremblings, is not safe in the greater shocks. Again and again large areas in southern Italy have been almost swept of their buildings by the destructive movements which occur in that

most is known, the shocks have never been productive of extensive disaster. In fact, the reiterated slight jarrings which attend volcanic action appear to prevent the formation of those great and slowly accumulated strains which in their discharge produce the most violent tremblings of the earth. The greatest and most continuous earthquake disturbances of history-that before noted in the early days of this century, in the Mississippi Valley, where shocks of considerable violence continued for two years-came about in a field very far removed from active volcanoes. So, too, the disturbances beneath the Atlantic floor

t earthquakes of the stronger kind are generally formed by the riving of fissures, which may or may not be developed upward to the surface. This view is supported by many careful observations on the effect which certain great earthquakes have exercised on the buildings which they have ravaged. The distinguished observer, Mr. Charles Mallet, who visited the seat of the earthquake which, in 1854, occurred in the province of Calabria in Italy, with great labour and skill determined the direction in which the shock moved through some hund

for earthquake). Then on either side of this plane, which indicates the line but not the depth of the disturbance, other observations may be made which give the clew to the depth. Thus a building may be found where the northwest corner at its upper part has been thrown off. Such a rupture was clearly caused by an upward but oblique movement, which in the first half of the oscillation heaved the structure upwardly into the northwest, and then in the second half, or rebound, drew the mass of the building away from the unsupp

ertain realms, as in southern Italy, a part of the failure of the people to advance in culture is due to their long experience of such calamities, and the natural expectation that they will from time to time recur. In a similar way the Spanish settlements in Central and South America, which lie mostly in lands that are subject to disastrous shocks, may have been retarded by the despair, as well as the loss of property and life, which these accidents have so frequently inflicted upon them. It will not do, however, to attribute too much to such terrestrial influences. By far the most important element in determining the destiny of a people is to be found in their native quality, that which they owe to their ancestors

bar supported near one end by two wires, one from above, the other from below. It may readily be conceived that any measurable movement will cause the longer end of the rod to sway through a considerable arc. Wherever such a pendulum has been carefully observed in any district, it has been found that it indicates the occurrence of slight tremors. Even certain changes of the barometer, which alter the weight of the atmosphere that rests upon the earth to the amount indicated by an inch in the height of the mercury column, appears in all cases to create such tremors. Many of these

a place in the Apennines, where two buildings separated by some miles of distance are commonly intervisible over the crest of a neighbouring peak, it has happened that a change of level of some one of the points has made it impossible to see the one edifice from the other. Knowing as we do that the line of the seacoast is ever-changing, uprising taking place at some points and down-sinking at others, it seems not unlikely that these irregular swayings are of very common occurrence. Moreover, astronomers are beginning to rema

gue of the loss of life in the accidents of this description which have occurred during the Christian era has led the writer to suppose that probably over two million persons have perished from these shocks in the last nineteen centuries. Nevertheless, as compared with other agents of destructio

by thousands of years. Thus, on inspecting a country such as North America, where the historic records cover but a brief time, we may on inquiry determine which portions of its area have long been exempt from powerful shocks. Where natural obelisks and steep taluses abound-features which would have disappeared if the region had been moved by great shocks-we may be sure that the field under inspection has for a great period been exempt from powerful shaking. Judged by this standard, we may safely say that the region occupied by the Appalachian Mountains has been exempt from serious trouble. So, too, the section of the Cordilleras lying to the eas

e violent inundations that they lose many features which are often found along coasts that have been exempted from such visitations. Thus wherever we find extensive and delicately

g exemption from strong earthquakes in

which are produced during heavy storms. At the present time the waves formed by earthquakes appear to be of destructive violence only on the west coast of South America, where they roll in from a region of the Pacific lying to the south of the equator and a few hundred miles from the shore of the continent, which appears to be the seat of exceedingly violent shocks. A similar field occurs in the Atlantic

of Geolog

. Some astronomers, basing their conclusions on the heat-containing power of matter, and on the rate at which energy in this form flows from the sun, have come to the conclusion that our planet could not have been in independent existence for more than about twenty million years. The geolog

ot in about five thousand years, or two hundred feet in a million years. Discovering at many places on the earth's surface deposits which originally had a thickness of five thousand feet or more, which have been worn down to the depths of thousands of feet in a single ra

n, he comes upon one of those breaks in the succession, or encounters what is called an unconformity, as when horizontal strata lie against those which are tilted. In many cases he may observe that at this time there was a

they now are. Granting all that can be claimed on this score, we note the fact that the rate of erosion evidently does not increase in anything like a proportionate way with the amount of rainfall. Where a country is protected by its natural coating of vegetation, the rain is delivered to the streams without making any considerable assault upon the surface of the earth, however large the fall may be. Moreover, the tides have little direct cutting power; they can only remove detritus which other agents have brought into a condition to be borne away. The direct cutting power of the tidal movement does not seem to be much greater in the

of beds has been accumulated in that part of geologic time during which strata were being laid down in the fields that are subjected to our study. Although in these rocks there are many sets of beds which were rapidly formed, the greater part of them have been accumulated with exceeding slowness. Many fine shales, such as those which plentifully occur in the Devonian beds of this country, must have required a thousand years or more for the deposition of the materials that now occupy an inch in depth. In those sections a single foot of the rock may well represent

y constructed series of elevations may readily be observed. Of old, it was believed that mountain ranges were suddenly formed, but there is, however, ample evidence to prove that these disturbed portions of the strata were very gradually dislocated, the rate of the mountainous growth having been, in general, no greater in the past than it is at the present day, when, as we know full well, the mov

turalist who has obtained a clear idea of the facts will question the statement that they are not a thousandth part of the alterations which have occurred since the Laurentian time. The writer is of the opinion that they do not represent the ten thousandth part of those vast changes. These changes are limited in the main to the disappearance of a few forms, and to slight modifications in those previously in existen

r this interval. Some of the students who have approached the subject are disposed to allow a period of at least twice this length as necessary for the perspective which the train of events exhibits. Reckoning on the lowest estimate, and counti

that the advance in the organic series has been more rapid in recent time than at any stage of the past. In a word, all the facts with which the geologist deals are decidedly against the assumption that terrestrial changes in the organic or the inorganic world ever proceed in a spasmodic manner. Here and there, and from time t

ons as to peculiar methods of action are introduced into the interpretation. It required many centuries of labour before the students of the earth came to adopt the principle of explaining the problems with which they had to deal by the evidence that the earth submitted to them. Where

have apparently now been traced down to near the Cambrian level. In other words, at the stage where we first find evidence of living beings the series to which they belong had already climbed very far above the level of lifeless matter. Few naturalists will question the statement that half the work of organic advance had been accomplished at the beginning of the Cambrian rocks. The writer

on that the records of those strata have been subjected to numerous and immeasurable breaks, while the development of organic life has of necessity been pe

Mo

ys-the moon offers a most profitable object to the student of geology. H

e solar system. After the earth-moon body had gathered into a nebulous sphere, it is most likely that a ring resembling that still existing about Saturn was formed about the earth, which in time consolidated into the satell

luid by heat; further on, they entered the rigid state-in a word, they froze-at least in their outer parts. At this point in their existence their histories utterly diverge; or r

s fancied that our satellite had seas and lands like the earth. The first telescopes did not dispel their fancies; even down to the early part of this century there were astronomers who believed the moon to be habitable; indeed, they thought to find ev

are probably not over as many feet across. The writer, from a careful study of these pits, has come to the conclusion that the wider are the older and the smaller the last formed. The rude elevations about these pits-some of which rise to the height of ten thousand feet or more-constitute the principal topographic reliefs of the lunar surface. Besides

mountains near

lesser size and probably of latest origin-extend in some cases for five hundred miles or more across the surface. These light bands have never

lines of the edge of the satellite in a solar eclipse. The same evidence shows that there is no vapour of water; moreover, a careful search which the writer has made shows that the surface has none of those continuous down grades which mark the work of water flowing over the l

place, we see on the extreme border of the moon, when the libration turns one side the farthest around toward the earth, the edge of a number of the great walled pits such as are so plenty on the visible area; it is fair to assume that these rings are completed in the invisible realm. On this basis we can partly map about a third of the hidden side. Furthermore, there are certain bands of light

a matter of very great difficulty. The main points seem to be tolerably clear; they are as follows: The surface of the moon as we see it is that which was formed when that body, passing from the state of fluidity from heat, formed a solid

-which is in progress in the seas and lands and is to endure for an inconceivable time to come-has been denied our satellite, for the reason that it had no air with which to entrap the solar heat and no water to apply the solar energy to evolutionary processes. The heat which comes upon the moon as large a share for each equal area as it comes upon the earth flies at once away from the airless surface, at most giving it a temporary warmth, but instituting no geological w

most debatable of all that relates to that sphere; we shall therefore have to content ourselves with the above brief statements as t

n studyin

ways in which he may best undertake to trace the order of events exhibited in the phenomena of the earth. Following the plan pu

verlook the fact that the soil beneath our feet is not mere dirt, but a marvellous structure, more complicated in its processes than the chemist's laboratory, from which the sustenance of our own and all other lives is drawn. We feel our own bodies as dear but commonplace possessions, though we should understand

ecessity falls into the commonplace way of regarding the facts with which he deals. If he be an astronomer, he catalogues the stars with little more sense of the immensities than the man who keeps a shop takes account of his wares. Nevertheless, the real profit of all learning is in the largeness of the understanding which it develops in man. The perio

e mental picture of the thing. In all education in Nature, whether the student is guided by his own understanding or that of the teacher, a first and very continuous aim should be to enforce the habit of recalling very distinct images of all objects which it is desired to remember. To this end the student should practise himself by looking intently upon a landscape or any other object; then, turning away, he should try to recall what he has beheld. After a moment the impression by the sight should be repeated, and the study

man, this understanding of spacial relations is very clear and strong. It enables the primitive man to find his way through the trackless forest, and the carrier pigeon to recover his mate and dwelling place from the distance of hundreds of miles away. In civili

should be platted. After a time to these indications should be added on the map lines indicating in a general way contours or the lines formed by horizontal planes intersecting the area subject to delineation. After attaining certain rude skill in such work, the student may advantageously make excursions to districts which he can see only in a hurried way. As he goes, he should

two classes of facts-those exhibited in the rocks as they actually appear in the state of repose as shown in the outcrops of his neighbourhood, and those shown in the acti

er was accustomed to have students compare their work of observation and delineation with that done by trained men on the same ground. It now seems to him best for the beginner at first to avoid all such reference of his own work to that of others. So great is the need of developing independent motive that it is better at the outset to make many blunders than to secure accuracy by trust in a leader. The skilful teacher can give fitting words of caution which may help a student to find the true way, but any reference of his undertakings to masterpieces is sure to breed a servile habit. Therefore such comparisons are fitting only after the habit of free work has been well formed. The student

the field with which he is enabled to deal in the actual way that he can transfer experience thus acquired to other grounds. Therefore beyond the pleasing views which he may obtain by reading certain general works on the science, the

ears to be directed. So far as the student observes well, and thus gains a clear notion of separated facts, he is in a fair way to gather the data of knowledge which may be useful; but the real value of these discernments is not gained until the observations go together, so as to make something with a perspective. Until the store of separate facts is thus arranged, it is merely crude material for thought; it is not in the true meaning science, any more than a store of stone and mortar

DE

Moun

cult

ican

inning swamp

velopment

ges on the c

food under

e, on the

volution of

ical experimen

l, in cavern d

wells,

ce of Itali

roid

their centres and

solar system an

nomy,

e the time of G

st scie

here,

tropical

unication between d

er, containing

the science

e movements

of the

low wall during the pa

ing power

which it

ater

nfluence on the surfa

fied by the condition w

untai

seash

e ear

e sun

n evidenc

of underground

s of, 1

of the, next t

motion of t

culation of the

lope

boreali

ches,

the Alpine r

Swiss Oberla

, 175

x

anges in the

rth's rot

lined posi

g movement of

planetary spheres

es of changes i

lts,

, 93, 1

r, 142

ly,

d,

of, on the s

astronomers about

rund, t

tributing to the fert

eting,

o

ng, 33

, 33

334,

ing,

id advance

rs, 21

, 135, 1

natural,

of Ma

formed river

acts,

253-2

ture of,

ater,

h cave

lagmites on the roo

s, 14

ry, 6,

ce of

rom the studies of

osphe

of the Icel

-beaten, 13

im

modifications of th

the ocean

lf Stream

ds,

on of,

e of

usually fr

ng, laws o

as

the Scand

t of tide o

enland

ersey si

change

Siberi

s, 47

ions o

meteorite

amity to the

, of 1811

e under V

n religion and

countries and the fol

tal shel

ts and o

n positio

s of th

s of

have endured fo

of,

eefs, 1

realm of

See under

arrier to the

e wate

ds,

ren

rida affecting the

orial

lf Stream

ld, of the

an,

on of trade

migratio

indicat

history

near the eq

ones

e of

h Ameri

y storms

s, 17

, vein,

, inter

159

t of cloudle

getati

on of,

erets

of a v

elopment of

arth's surface may be

f mangro

the fulcrum point in the mov

r sphere at th

e ear

92, 293;

n volcanic

through

upwar

on of,

l of, 3

vements of soft

on to volcan

the material

s produce

of,

Swamp,

tan

l idea

to stud

ldiers to m

ms, 10

f the equ

hurrica

of a country affect

, 124, 325

ded,

geological

ions from wind

rt

ened sp

lope of

falling from th

ty of t

ere of

g power o

e rotation

f the atmosph

, affected b

the path of t

er of

cted by loss

titude of the su

t it was glob

changes in the relat

nterior heat of

he sun on t

n a fluid

w of the, fro

ure of the sur

used by fa

rmined by heat and l

eature of the su

cting the direction

ents,

hitecture o

, exempt from

f the moo

round the sun,

rom east to

, from daily esc

ering of

of the

ing,

, proble

chemical changes

belt of

surface of the

ore of t

278, 280, 356, 358

nts of

n of,

degradatio

s of

itations to

, of 1883,

architect

s, 36

of, 37

ect

e soi

e of the e

iving of fi

ks have been disturbed by

Pompeii destroye

in 1783,

nected with volcan

in 1692,

55, 368, 369,

swing

e liability

sm of,

f, followed by Mr. Ch

in 1811, 373,

the earth

m a fault plane

from the sea

ation

ting a long exempti

a, in 1

their effect up

alamities of

s of

orms,

od underg

ecord of an

n the formation of

of seas and

ndestruc

lower, of

ua

our sphere

m of t

t under

current ne

recession of

rs,

in a hollow wall during the

lidation of disseminated mater

See Wat

planes

spar

s, 18

in New En

east of Rocky

ns,

salicif

zation,

m poin

ic pla

, eruptio

work of wat

n the valleys of

, 63, 2

thern hemi

te,

cia

ect

h Ameri

al Ameri

Americ

rs, 20

ce in formi

kan,

al, 225,

rge of

ring,

reenland and Sc

North Ameri

raines near Mo

ns of

the, 228,

the under i

of a

the Swiss v

the rocks r

with winter

ey,

dge, 1

tion, l

ea of the

ically inv

, current o

e

y escaping from

ng from the sun

e ancients r

on air currents

hich it leave

ern

earth,

h's interio

the atmospher

elief regarding t

e earth's, caus

ar,

and air cu

, san

al pendu

atitude

ses,

es, 107,

ement o

um of

ar the

tropi

oth

34, 35, 3

ing,

ac

intense,

glaciers,

es in Greenl

in Green

on river ch

on stream

when fre

92, 9

ting

rarely fe

t, in Greenla

by press

re

ntal, 2

mountai

alayan Mou

gs, 24

oceanic cur

anic eruption

first, astron

chanical, aidi

ds, 8

nenta

made up of volcan

anic

-lanter

pi

wraps

earth affect

planet of

es,

, and nebular

in,

trict, cold

kat

n of, 2

, on the

, on the

ites,

ine bed

t deposits f

bas

on of,

331, 3

ts, 35

, 199

n the river

-wate

rom cave

ging their

ct volca

atures of th

anic

nd

tively unch

le,

g in change of coa

he seas an

changes in the at

, divisio

urface

as to the divisi

shape o

forms of

e, troublesome

nebular hy

, 271, 292, 293, 2

nvading a

esuviu

9, 295

ure of,

ient,

ks of,

eaves,

nat

otle

vitati

ervation of

radiatio

affected by tid

surfac

c, evolution

of the ancient

ng, 24,

from

the earth to t

of building

ring-out ef

353, 357, 35

on of,

hquake of, 1

ival, observatio

s near the Gul

rel s

and the study of ea

inventor o

oves,

ing mode of

es of

and moraines nea

ch marsh

th contour

a

e study of celest

ic sketc

jeopardizing ag

s, sustenance

325-327,

es, 3

d by earthq

65-67,

it has an at

ls o

wraps

escopes required f

earth than oth

rs

rove

Ipswi

e, 33

s found

h Ameri

t of New En

na of,

earth for

North Am

y, 55,

to the

ompletes the circl

ites,

of comet

ors,

ing,

ition

g, 39,

d of

friction w

studying ge

y Wa

the path of

crusts,

sits

38, 39

ir and water

by satell

h it exercises

eature of

seous or aqueou

r of th

w of the eart

on" of t

cular depressi

ts of t

phere in

the earth

, in relation t

tion and

f the,

ot act in the same

216, 218

s and, near Mo

s of the

inal

in,

?tna,

ding, 290

m caves of

ul than Ves

ties of,

of, 2

the torre

uilding, 9

86, 87,

cooling of t

th,

fall

, energy

5, 86, 89, 9

structu

escape of heat fr

ons o

a, formati

263-285, 288, 28

e eruption of, in

ough, showing changes in

of, in

-'83, 2

of, in

increased si

lava f

on a period of i

, in 1882-'

perity of th

othesis, 34

une,

the,

g in the regi

elief regarding the

alls, 191

back o

h Am

the form

lar for

ea

depth of

effect of

ents

, on migr

on organi

r, 8

d currents

of the

of sedimentar

f the,

n, effect of, on t

nd conti

bi

the, and the

g of th

of the

315, 317, 321,

on the soil

f the shore

of in the se

cean curren

of, in the

in the e

on,

he shores of the

a river,

nd cut-o

bb

seaweeds

he waves on

spher

ins

, 179, 182,

ry of

d,

ets,

by satell

ve sizes

solidation of disseminated m

wraps

by the ancients of fixe

nts of

er,

tive masses o

the Sargassu

and a

ecti

cal contri

the roots of, on

loving

limbing b

nodding move

snow c

s, 15

circula

es, 34

on of h

6, 164, 168,

of the,

orce of,

al form

in the formation

of th

nseen so

ds,

igi

ween science

tween pagan

and déb

ourse of, in all

ccelerated by tr

lways cl

Mississippi, eat

s,

d, cutting

ow-ic

f a norm

f a, 18

ng of

ovement of

lleys, 1

n the form

ks,

from fal

by sandst

by crevi

vents recorde

of, mater

g of,

on of,

y to the strata of

ion of

long exemption from s

in, 25

of, 349, 350,

e, in regard to

olcanoe

elasticit

on of,

, march of

, 250

earth affected

ry spheres on

ed fores

s formed in

lakes,

bars,

, against th

ravellin

hing

nes cutting a

ites,

heir centres and ab

38, 53,

bands

wraps

earth affect

tive, students

hanges on the

ie

to mechanical

beginnin

haracterist

ween religio

een the Roman

ventions as a

and anc

ral,

n Aristotle

siolog

in Aristotl

ctically on

fic dev

outline

ing and weighing, as

e

action o

changing,

canic eruptio

the, affected by v

rganic and mine

d currents

one of the

s,

ganic life

ction of

formatio

inerals

, 155

s,

y living

f, buoy

seat of salt de

ent as to divi

f the,

, air of

ng the characte

hearing

ight

ell,

ste,

uch,

cs,

uake. See unde

, variation

cliff,

holes

e districts

ap

n of, 2

the erupti

ackere

207-22

nce of atmo

owers beginning to

e between an annual

f, on pl

in the formation

formatio

, 2

es,

enomena of

o

al, 32

circulation

ing to formatio

motion of

of the ea

f the,

on of the

correcting

fields greater than t

and ashes an inte

f, in desert

ls and plants o

arthquakes

istinguished from t

, affected b

on of,

aracteristi

ted, 3

n of the,

riation

ral,

tile when subjected

r blown s

e derivatio

mena,

organic lif

on in,

rotecting th

ay of the,

from the

ants on

duty of

r bo

ditions of

on of, on th

m, 52

om the fixed s

vapour of

features

e,

he

in magnit

of the

ation of, on t

, sun

ng hor

rmation of

itizati

tites on the roof and

bodies in th

aunhofer and ot

ble

al acti

t study

rvations by the ancie

ated sun

in the lig

en by the na

ne star about a

ting

f certa

of,

forth of, due to

rough the

wander

realm,

or

ular

t, 12

ned in a hollow wall du

nciple of

Sahar

re frequent i

s of

, of cycl

ning

er, 1

ng, 10

culiarity o

writings

u

ere of

tion of

the earth

anges in the,

of the, 7

solidation of disseminated m

dark and

he eight plane

aving t

of th

ney from the,

f the,

earth arou

ondition o

elief regarding t

ts,

certain in

n revealing

roblem before the use

ve masses of, a

in the histor

es,

t in the same mann

es, le

swayings

am

owing rema

Swamp,

e of, 3

ater, 3

na of,

-land

e masses of sun

pes, 11

esults

r of

tions

erat

produced by

oldrum b

h Ameri

lantic Oc

rate of,

der,

ced in the m

torms, 1

tion of,

l ac

udies of,

North Ame

de

channe

e earth's ro

on marine

of, 1

d sun,

run of

tion o

rade win

ar,

ng of, 1

g air into the por

s, 112,

pment

, on buil

n North Am

h of,

of, to hur

action of,

s, 177-

ds. See u

g in la

g visual m

measure di

intervals o

turalist

, natur

nus

formed from disturban

ll

the form of r

er,

56, 157,

attraction

theory o

the solar s

eta

dew,

independent

the soil,

agram of

s, 6

ns of, by Mr. Per

stem, study

See Moun

g memories

action,

uption of a

cts concerni

nds,

mary featu

f, made from a

e floor of the

matter beyond control of

s, 125,

on the sea

rom eruptio

Pacific

intaining fertilit

ution o

of, 286

from a supposed liquid i

earth mate

water

dered collecti

of and the history

earth after erup

of, 2

na of,

rine,

ejections fr

te

ice,

earth,

ction of,

om the po

Arctic Circle to th

value

of, in r

l work of

air

ds usually

er for cutti

250,

nerals

the ear

of, 1

ical

he, under the

way rocks

ying mineral matt

eading to changes in r

rbonic-acid

ons of

way rocks

of,

alls,

e of

semite

a, 191

torrent district

d by di

manufactur

outs, 1

ric caus

g at,

of a,

queness

r of fre

28, 129,

friction o

of the

f sand agai

, 133, 1

sed by eart

thquak

ures in the a

f, 137

of th

f,

eight o

tions

d,

e of, on the

made,

ns of studyi

f the s

tesian,

fluids and

ds in Sa

-the-wi

01, 110,

of sa

cane,

f how they are

a's Vine

sts, work o

oes, effe

nd of Jamai

n of t

ng away in the

-105; 145,

on ocean cu

motion of th

n of the oc

unter-flow

of th

ndition of

k of, 132,

ief of, in the

pid advance

ot have been supplying heat as at present for more than about ten million years, and that all g

ar Astronomy, p. 234. H

s is afforded by the depths of a wood, the eye is apt to imagine the appearance of faint lights. Those who have had to do with outpost duty in an army know how the anxious sentry, particularly if he is new to the soldier's trade, will often imagine that he sees lights befo

eing allowed to fall into water which chills them. Iron shot, used in cutting stone, where they are placed between the saw and the surface of the rock, are also made in the same manner

shores of arid lands, where the sea occasionally breaks over the beach into th

ble life may develop on a frozen surface, drawing their sustenance from the air, and supplied with water by

n down. This is the natural end of these features. As before remarked, they are but the

phrase "lava-yielding" for the reason that the

ius, the patron of Naples, have been accustomed to carry his relics in procession whenever an eruption began. The cessation of the