« ForrigeFortsett »
vpper part and runs off by a tube m placed at the top of the the supposition that this liquid has the same density as the vessel. The distillation must not be pushed too far, lest the water in the vessel E. Now, as the distance or is less than water should contain organic matters which might be decom- the height D y, the air enters by the orifice o before the water posed on the hot sides of the cucurbite, and originate volatile of the vessel rises up to a, and no absorption takes place. The products.
tube co serves also to prevent explosions. When the proDistilled water is perfectly clear, and leaves no residue after duction of the gas is too rapid, and the tube Ad is not suffiits evaporation ; but it always contains a little carbonic acid ; cient for its generation, the liquid contained in the flask m is for this gas existing in all natural waters, is but imperfectly forced out and esapes by the tube c, which becomes an issue separated from them by distillation. The presence of this gas for the gas as soon as the level of the liquid falls below the may be avoided, however, by putting into the cucurbite a cer- orifice o. tain quantity of lime, which combines with it, and retains it. Another kind of safety-tube, called an S-tube, is represented It is by distillation, in alembics analogous to the preceding, in fig. 197. This tube has a bulb, a, containing a certain that we extract from wines the alcohol they contain.
quantity of liquid, as well as the branch id. Safety-Tubes.-An occurrence which is often produced in the preparation of gases in chemistry, and which is called
Fig. 137. absorption, consists in this, that when gases are collected over water or over mercury, these liquids enter the apparatus, and render the operation useless. This occurrence arises always from the excess of the pressure of the atmosphere above the pressure or tension of the gas contained in the apparatus. Thus, in fig. 195, suppose à gas, say sulphurous acid, be generating in a flask m, and passing over into a test-glass, A, full of water; so long as the evolution of the gas goes on, its tension is sufficient to overcome the pressure of the atmosphere and of the column of water on; the water of the test-glass cannot rise in the tube, and absorption is impossible. But if
When the tension of the gas in the retort exceeds the pressure of the atmosphere, the level in the branch i d rises higher than that in the bulb a; if the gas has the tension of one atmosphere, the level sinks in the branch id, and as we take care that the height i a is less than 6 h, as soon as the air admitted by the funnel centers into the bent part i, it raises
the column i a, and enters into the retort before the water of the tension of the gas decreases, either because its evolution has the test-glass rises to b; from this instant, the interior tension ceased, or because the flask has been cooled, the exterior is equal to the exterior pressure, and absorption is prevented. pressure becomes the greater, and when the excess of this pressure above the interior pressure surpasses the weight of the column of water co, the water enters the flask, and the operation fails. This occurrence is prevented by means of safety-tubes. These tubes are employed to prevent absorption,
LESSONS IN GEOLOGY.-No. LII. by admitting the air into the apparatus, in proportion as the interior pressure decreases. The simplest invention of this
BY Tuos, W. JENKYN, D.D., F.R.G.S., F.G.S., &c. kind is an upright tube co, fig. 196, which passes through a
CHAPTER V. cork fixed in the flask m, in which the gas is generated, and immersed a little way in the liquid contained in the flask.
THE CLASSIFICATION OF ROCKS.
THE CHALK FORMATION.
The entire group of rocks, called the Cretaceous formation,
1. Maestricht limestone and Faxoe chalk.
3. Lower white chalk, without flints, passing into chalk
2. Firestone greensand,
6. Lower greensand, with iron sand and occasional beds of limestone, called Kentish Rag.
1. THE LITHOLOGICAL CHARACTER OF THE BEDS,
1. In England, the uppermost bed of this formation is the When the tension of the gas in the flask a diminishes, the white chalk with Aints; but on the Continent, at Maestricht pressure of the atmosphere which acts on the water in the in Belgium, and at Faxoe in Denmark, there are two beds of Pessel 2, tends to force it up the tube D A, to a certain height; more recent formation than the upper chalk of England and but this pressure acting also in the tube or, tends to force France. down the liquid which is in this tube, to the same extent, At Maestricht, on the banks of the river Meuse, there is,
resting on the white chalk with fints, a peculiar bed of calca- consists of a series or alternations of sands, sandstones, lime-
1. Sand, white, yellowish, or ferruginous, called Shanklin
The whole of these six or eight beds are called the cretaceous yellow limestone resting on bed No. 2, white chalk with formation. The term “cretaceous is more comprehensive Aints. This limestone is formed of corals, and is used for than "chalk," for the word "chalk” is limited to the soft building stone. Its thickness is unknown. Some portions of white mass of carbonate of lime; but the term “ cretaceous" this bed consist of white earthy chalk.
comprehends a group of deposits widely dissimilar in litiolo. 2. The Upper White Chalk, Bed No. 2, is that white earthy gical character, though agreeing in organic remains, and, on limestone, so well known—soft enough for marking and writing, that account, referrible to the same geological epoch, called but generally too soft for building stone; and yet the lower it the "cretaceous." Whether the fossils be imbedded in soft goes the more solid it becomes. It wants only two parts out white limestone, or in blue clay, or in loose sand, or in compact of a hundred of being entirely carbonate of lime ; and, there- stone, they consist of species of the same genera of plants and fore, when burnt, it makes as good lime as the hardest marble, animals. In the south coast of the Isle of Wight, the entire and is used extensively in London and the neighbourhood.
series of the beds 2, 3, 4, 5, and 6, with the exception of its Wherever this bed is met with, it is known by being inter- lowest member, the Kentish rag, are exposed to view. stratified with flint, These flints are found, sometimes in layers a few inches thick, in continuous black sheets, or more
II. THE ORIGIN OF THE CHALK FORMATION, frequently, in nodules, at intervals of two or three feet from
1. The chalk, which, to the eye, appears a white soft mass, each other.
consists, in reality, of very minute microscopic shell-fish and 3. The Lower White Chalk, Bed No. 3, is a very deep mass corals, so exceedingly diminutive that a cubic inch of chalky of white chalk, but destitute of Alints. The chalk of this bed is matter contains, at least, a million of organic remains. Even harder than that of No. 2. In many places, as about Dover, a blot of whitewash made from chalk exhibits, when examined the chalk of this bed is so solid and firm as to constituie by a good microscope, a beautiful patchwork of these small a good building stone, is extensively blasted, and then squared shells, which were the calcareous cases of animalculæ called for sea walls and other durable buildings. The abbey of St. foraminifera. All these foraminifera, and still more diminuOmer, in France, is built of this kind of chalk. In some parts tive infusoria, were once alive in the sea of the cretaceous of Yorkshire, and at Havre on the French coast, this bed con- epoch, and were widely diffused through its waters. When tains fints.
these minute organisms died, their shells were deposited as 4. The Firestone Greensand, Bed No. 4, is most frequently white mud at the bottom of a very deep sea, and contributed, called the “Upper Greensand." It had been well if either by accessions for ages, to form the deep beds now called this bed or No. 6 had been distinguished by some other name chalk. than "greensand," for the sake of beginners... As the upper Independently of the aid of the microscope, analogy had part of this bed forms a coarse calcareous limestone called early suggested to some geologists the probability that chalk, PIRESTONE, perhaps the term may be allowed as sufficiently even where every trace of organic structure had disappeared, distinctive of it.
was the result of the decomposition of shell-fish and coral. The bed of chalk without flints passes downward, as you First. In the Bermuda Islands there are several lakes or have seen, into a clayey limestone called “chalk marl," and lagoons almost surrounded by reefs of coral, and at the bottom in some places “clunch." Under this clunch are beds of of these lagoons is found a deposit of calcareous mud, soft and sand abounding with green particles which are silicate of iron, white, formed by the death and decomposition of coralline and which give their name to the beds. The sandy particles animals, such as the Flustra and Cellepora, Specimens of this are united by a calcareous cement, occasionally containing mud, when dried, cannot be distinguished from the ancient either beds or else nodules of chert and chalcedony.
chalk. This formation is very extensive in England. If a man Secondly. Among the coral islands of the Pacific, especially were to travel in somewhat of a zigzag direction from Haldon near coral reefs, a soft and white mud is found at the bottom, Hill, west of Exeter, to the neighbourhood of the river Humber which has every evidence of having passed through the bodies in the north of England, he would be in constant company of the worms that built the coral rocks; and other parts of it with this bed. In parts of Surrey, as about Reigate, the upper through the intestines of fishes. Hence the origin of the part of it forms a calcareous rock called firestone, and some coprolites. In the clear waters about those rocks, large shoals times Merstham stone.
of the fish Sparus can be seen feeding quietly on living corals, In the cliffs of the Isle of Wight, about Black Gang, this like cattle on a field of buttercups. bed is 100 feet thick, having bands of flinty limestone and limy Thirdly. At Faxoe, in Seeland, Denmark, small portions of sandstones with nodules of chert. These nodules of chert and that remarkable rock consist of white earthy chalk formed by chalcedony become more prevalent in the south-western parts the evident decomposition of corallines. of England, as on the Blackdown in Devonshire. At Sidmouth 2. Flints are found sometimes in veins, and sometimes in the sea-shore abounds with these pebbles. In the Blackdowns nodules, from the size of a nut to masses many feet in circumthere are quarries which furnish the scythe stones and build- ference. The nodules occasionally appear as vertical and ing materials. This stone, when just exposed in the quarry, is diagonal veins, filling up fissures and crevices, and traversing soft and easily tooled and dressed, but it soon hardens by both the chalk rock and the sheets of tabular fint. This face exposure to the atmosphere.
deserves to be noticed, as it proves that the lower bed of chalk 3. The Gault, Bed No. 5, is a bed of stiff marl, or dark blue No. 3, had been consolidated and made hard before the superclay, with thin layers of red marl, and intermixed with green incumbent bed No. 2 had been deposited, and before the Band. It is well developed at Folkstone in Kent, and at Black streams of siliceous matter had flowed over it. Gang in the Isle of Wight. In the south-east of England this Flints, whether in nodules or in veins, were probably probed is 100 feet thick; and by its organic remains it can be duced by heated water and vapours occasioned by volcanic traced to distant parts of Europe, and to the Alps. This heats below. That the flinty substances were once perfectly formation has, latterly, become famous among agriculturists, soft and fluid, is proved by the sharpness of the moulds and for the extensive beds of phosphates of lime which have been impressions of shells found in them. There would also be in found near Farnham, in Surrey, and elsewhere. These phos- those seas minute animalculæ that had siliceous or finty, phates consist of coprolites or the excrements of fish, and are instead of calcareous, shields or shells, such as sponges, which found most abundant in the gault and the greensand above it would serve as the base for the aggregation of siliceous matter. 6. The Shanklin Greensand, No. 6, is generally called the
3. The minerals which are found in connexion with the "lower greensand,” because of its lying beneath the gault. It chalk formation, such as small pebbles of quartzose sandstone,
of jasper, and flinty slate, also the grains of chlorite, and mica, 4. Among the most conspicuous fossils of the white chalk are and silicate of iron, indicate the nature of the pre-existing the Belemnite, Baculite, Ammonite, No. 6, and Turrilite, No.4, rocks, whose destruction and wearing down produced the green and the Cidaris Diadema, No. 2. The Terebratulæ, like No. 3, are sand and other beds.
very abundant, being the shells of a species that live at the bottom
of the sea in tranquil and deep water. With these are associated III, CRETACEOUS FOSSILS.
many corals and sea-urchins, all of which are marine animals, 1. Though the Maestricht chalk is newer than any creta- whose remains indicate a deep sea. In this bed, some of the ceous bed that is found in England, its fossils are quite dis. iinty nodules owe their irregular and grotesque forms to certinct from the tertiary species, and yet some tertiary volutes tain zoophytes which they enclose, or to the branches of a and other genera of tertiary univalves, occur in it. One pecu- sponge. In some portions of the upper chalk the only remains liarity of this bed is that it has a few species of shells common of fish are the teeth of the shark family, in part common to to the lower white chalk, the bed No. 3, such as the Belemnites the tertiaries, and in part extinct. We find here no bones of mucronatus, and the Peoton quadricostatus. It is particularly land animals, no river shells, nor any plants, except sea-weeds, celebrated as the bed in which were found the remains of à and occasionally a piece of drift-wood. The fossils of the white great marine reptile called Mososaurus, the Saurian of the chalk near Maidstone, in Kent, show that turtles, and eggMeuse, supposed to have been twenty-four feet in length. laying saurians or lizards, and the winged lizard called This fossil was discovered in a soft freestone.
Pierodactyl, lived at this epoch, and their imbedded remains 2. The shells found imbedded in the chalk of Faxoe in See- indicate the neighbourhood of land near that part of the ancient land, are chiefly casts. Many of these are univalve shells sea where they perished, which belong properly to the chalk era, and are yet absent 5. The blue marl bed called Gault, has many peculiar forms from the white chalk of Europe. It has more than thirty of shells, such as the Scaphite, No. 5. It is in connexion univalves, such as Cypræa, Mitra, Cerithia, etc., not one of with this bed also that the coprolites have been most abundwhich is common to the white chalk ; and yet a great propor- antly found. These masses were once called the cones of the tion of its bivalves, corals, and Echinoderms are, in species, the larch, but they are now known to be the excrements of fish, same as those of the lower chalk formations.
6. The foșsils of the Shanklin sand, or "lower greensand," 3. The annexed illustration, fig. 3, represents some of the are, in species, distinct from those found in the higher chalk organic remains found in the white chalk, and in the different beds. A very peculiar forsil is the shell called Hippurites, beds which underly it.
No. 1, & species which seems to be characteristic of the creta.
', Lippurites organisaas. 2. Cidaris Diadema or Diadema Rotulare (Agassiz). 3. Terebratula Semigl bosa. 4. Turrilites
Catenatus. 5. Scaphites Equalis. 6. Ammonites. 7. Crioceras Puzosianus.
ceous rocks of the South of France, Spain, Sicily, Greece, and much breath is drawn in, much retained, or withheld, ana other countries bordering the Mediterranean.
little given out at a time; and thus are produced those smooth,
pure, and gradually-increasing tones, which are appropriate IY, SOME GEOLOGICAL PIIESOMEXA CONNECTED WITII to music,--all the breath that is given forth being converted THE CRETACEOUS EPOCH.
into sound, and none escaping, that is not vocalised. In notes 1. The bed of the chalk formation must have been very of very short duration, singing and speech are, it is true, cicep, for the chalk of the cliff's of Dover is 620 feet above the brought nearer to a resemblance. But this resemblance is level of the sea, that of Welton Bacon, in Yorkshire, 809 feet, more apparent than real; as may be observed in the execution and that of Inkpen Beacon, in Wiltshire, is more than 1,000 of every good singer, which, in the most rapid passages, still fcet.
produces the genuine effect of song, as differing from speech, 2. The surface of the chalk, as it now appears, consists The resemblance is owing solely to the brevity of sound, in generally of bold heights, indented by corresponding deep such cases, which does not afford time for broad and marked acclivities, called coombes, which are deep furrows or valleys distinctions to be drawn by the ear. seroped out by currents while the rock was under the waters
The modes of voice which constitute speech, or are exempli. of the ocean. "These scoopings took place before the London fied in reading, are the following: clay came to rest on these valleys.
I. RADICAL STRESS. This form of force includes two modes, 3. These furrows are excellent specimens of the aqueous -explosion' and 'expulsion.' process called denudation. The action of the sea upon the 1. 'Explosion' is an abrupt and instantaneous burst of Chalk rocks must have been intense and violent, as is attested voice,-as, for example, in violent anger. by the immense quantities of rounded flint, and worn-down This being an instinctive, unconscious, involuntary, impul. chert pebbles, contained in the stratum resting on the presentsive emotion, does not allow time or disposition for any intenchalk surfaces. This stratum of flint and other pebbles was tional or deliberate effect, but makes the creation of vocal formed by a muddy sea, whose waves brought down the flints soud seem an irrepressible, spontaneous, electric production from neighbouring chalk surfaces. Fine examples of this of nature, lying equally out of the reach of the understanding s'estum are found in different parts of Kent, but especially at and the wint. This tone has its contrast in the deep, calm, and Blackheath and Bexley.
regular swell of the tone of reverence, or the ample volume, and 4. Though the formation of white mud in lagoons teaches deliberate force, of conscious authority and command, in which us that the chalk rocks were not continuous throughout the the speaker is self-possessed and self-directed, and controls his whole of the districts where they are now found, yet many vocal effects for purposes understood or felt. valleys and plains furnish evidence that over the whole of Contrast, for instance, the following angry shout of Douglas their length and breadth, the chalk deposit lay once conti- when enraged by the defiance of Marmion, with the examples nuous and unbroken. This is the case with the valley of the of reverential invocation and authoritative command which occur Sour, in Dorsetshire, the vale of Pewsey, and Salisbury Plain, in the subsequent paragraphıs. in Berkshire and Wiltshire. That the chalk rocks were once continuous over the whole extent of these large districts is
Example of Explosion.' evident from the outliers of chalk or chalk marl left behind as
“UP DRAWBRIDGE! OROOM! What, WARDER, HO! meinorials, some of which are found even at Chard, in Somer
Let the PORTCU'LLIS FALL!” setshire, and the valley of the Axe, in Devonshire. 6. That the white chalk was formed in an open sea of great
The sounds of all the accented vowels, in this style, fall depth is evident from the fact that pebbles of stone, or drifted upon the ear with an instantaneous, clear, sharp, akrüpt, anh wood, are very rarely found in it. There have, however, been cutting force, at the initial or • radical part of each. instances in which pebbles of quartz and of green slate, some 2. “Expulsion,'-a conscious, intentional, and deliberate of then two or three inches in diameter, have been found. force, coming upon the ear with great power; as, for example, These pebbles could not have been volled by the waves from in the language of authoritative command. a neighbouring coast, for then we would have expec'ed that
Erample of Expulsion.' the same agency would have brought mud or sand to mingle with the chalk, which is never the case. The size of the
Vànguard! to right and left the front unföld!”
ble in the radical,' or initial part, of each sound. "Boui of
each sound. LESSONS IN READING AND ELOCUTION.
II, MEDIAN STRESS. This mode of force is exhibited in
1. ' Effusion,'-a moderate, gentle, and gradual swelling of
tone-as, for example, in the calm and tranquil utterance of
reverential fecling, in which no disturbing impulse anitate3 or è IX.-JUST STRESS,
forces out the breath, but the voice, somewhat as in music, The next characteristic of good reading and speaking, is glides out, with a smooth effusive stream of sound, calarging jest' 'stress. This word is meant to designate a peculiar
as it flows, but never bursting out into irregular violence modification of force, which distinguishes speech from music.
Example of. Ejusion.' A long-drawn musical sound has its most forcible part,-in cons quence of 'swell' and 'diminish,' at the middle portion
“But chiefly Thou, O Spirit! that dost prefer, of the note. The tones of speech, on the contrary--although,
Before all temples, the upright heart and pure, in a few cases, they approach to this mode of voice-usually
Instruct me, for thou know'st." have the chief force of each sound at the opening or the closing
The effusive' style aroids every thing abrupt or sudden in ent. In musie, the increase of foree is, comparatively, gra- the formation of sound, and sweils grusiually to iis acaso diwal ; in speech and reading, it is frequently abrupt. To these (chief point), at the middle of each sound –in the manica i
music; and from this point diminishes,' or decreases, to the To understand the application of this term, in detail
, it close. This species of stress is accordingly denomiurted becomes necessary to advert to the mode of creating vocal
median,' from the word medium, or middle. sounds. In vocal music, the result is obtained by full inspi- 2. “Suppression,'--& powerful force of 'explosion' or 'exration, (inhaling or drawing in the breath), and, comparatively pulsion,' kept down, in the very act of giving forth the voice, Bl ght'expiration (siving forth the breath). 'In this mode, I and converted into the median' form, as in the case of a
person communicating, in great earnestness of feeling, with VI, INTERMITTENT STRESS, OR TREMOR, The 'tremor,'
grief, and sometimes joy, when extreme. This mode of utter
ance characterises, also, the feeble voice of age, or the tone of Examples of Suppression.'
a person shivering with cold. 1. “Hark! James, listen ! for I must not speak loud. I do
Examples of the former will be found in the section on not wish John to hear what I am saying!”
Expressive Tones.” Of the latter we have instances in the 2. “Step softly! speak low! make no noise !"
language both of the old woman and the farmer in Words.
worth's ballad, “Goody Blake and Harry Gill."
Examples of Tremor.
1. “She prayed, her withered hand uprearing,
While Harry held her by the arm,--
are never out of hearing,
never more be warm!' 'aspiration, and made io assume the style of median stress.'
2. “No word to any man he utters, III. VANISHING STRESS. Besides the “radical,' or initial,
Abed or up, to young or old;
But ever to himself he mutters,
The word tone,' in elocution, may be used, as in music, to
commonly used as equivalent, nearly, to the term .expression'
in music, by which is meant the mode of voice as adapted, or Example of Vanishing Stress,"
not adapted, to feeling. Thus we speak of the tones' of
passion-of a 'false' tone-of a school' tone. " War! war!-no peace : peace is to me a war!"
Every tone of the voice implies, --1, a certain 'force,' or In tones of this class the voice withholds its force, and quantity,' of sound; 2, a particular .note,' or 'pitch; 3, a delays the explosion or expulsion, till the last moment of the given time,' or 'movement ;' 4, a peculiar stress;' 5, a emphatic sound, and then throws it out with an abrupt, special quality,' or character ; 6, a predominating interwrenching force, which resembles that of a stone suddenly tion. Thus, the tone of awe has a 'very soft force,' a very jerked from the hand. This species of stress, as it lies at the low pitch,' a 'very slow movement,' median stress,' and • vanish,' or last point, of a sound, is termed the vanishing ‘pectoral quality,' or that deep murmuring resonance, which
makes the voice seem as it were partially muffled in the
chest, together with a partial .monotone,' prevailing at the
Thus, in the tone of surprise, which is marked by a bold, [xx] Erample 1. “The bell | strikes | one. We tüke
ô nöte of time,
The first five of the properties of roice which have been
enumerated, are the ground of the following classification and
[•] ‘high ;' [oo] ‘very high ;' [o] • low;' [no] ' very low;'
[#] 'lively,'-(full tone); [ 6 ] ‘plaintive,'— (semitone).
of · Erpressire Tone.' sound.
+ Sce, 1X. STRE:S.'
KEY TO THE XOTATION OF