Francis Lieber.

Library of universal knowledge. A reprint of the last (1880) Edinburgh and London edition of Chambers' encyclopaedia, with copious additions by American editors (Volume 13) online

. (page 117 of 203)
Online LibraryFrancis LieberLibrary of universal knowledge. A reprint of the last (1880) Edinburgh and London edition of Chambers' encyclopaedia, with copious additions by American editors (Volume 13) → online text (page 117 of 203)
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waters of Shiloah that go softly;" jSehemiah calls it "the pool of Siloali;" and John,
""the pool of Siloam." Josephus says it was at the mouth of the Tyropoeon, where a
j mntaiu is still found. Jerome mentions its intermitting flow, which is siill observed.
' he water descends from the fountain of the Virgin through a long subterranean passage
J ito a basin under the cliff, and thence into a larger reservoir. That this passage con-
nects the fountain and the pool, Dr. Robinson proved by crawling through it from one
end to the oilier, a distance of 1750 feet. He witnessed also the intermittent flow in the
fountain, as well as the pool.

SILFHIUM, a genus of plants belonging to the order composite. Generic characteris-
tics: heads many-flowered, radiate; rays numerous, pistillate and fertile; ovaries in two
or three rows; disk flowers apparently perfect, but with undivided style and sterile;
scales of the broad and flattish involucre imbricated in several rows, broad, and with
loose, leaf-like summits, except the innermost, which are small. They are tall, coarse,
perennial herbs, having a copious resinous juice, and large corymbose-panick'd yellow
flowering heads. iSUpuium Idncinatum, called rosin-weed and compass-plant, is rough
and bristly, growing from 3 to (5 ft. high; leaves pinnately parted, witli divisions lan-
ceolate or linear, rarely entire: scales of the involucre ovate, tapering into long -and
spreading rigid points; achenia, or one-seeded capsule, broadly winged and deeply
notched, li grows on the prairies of Michigan, Wisconsin, and southward and west-
ward: blossoms in July, li is called compass- weed from its reputed propeity of grow-
ing so as to point its leaves to the cardinal points of the compass. Another species, S.
terebcut/uiKiceum, the prairie burdock, grows from 4 to 10 ft. high, with many small
heads in a panicle at the top; leaves ovate-cordate, serrate toothid, thick, rough, more
60 beneath, and from 1 to 2 ft. long on slender leaf-stalks. A \&r\(;\y.pintMiijiilum, has
deeply cut. or piuuatitid leaves. It grows on prairies and oak openings, Ohio, Mi.-hi-
gan, Wisconsin, and southward: blooms in July and September. Other species are 8.
trifohatuitt, 8. asterincus, S. integnfoLium, and S. perfoliatum, the cup-plant, which grows
from 4 to 8 ft. high, having ovate leaves, coarsely toothed, the upper united by their
bases, forming a cup-shaped disk; heads corymbose, and achenia winged and variously
notched; grows on rich soils along streams in Michigan, Wisconsin, and southwaid.
Also escaped from gardens eastward: blossoms in July.

EILTHIA'I HOCUS, a large division of the pnlccozoic rocks, between the old rod
sandstone and the Cambrian strata. They comprise the greater portion of the rocks
called by Werner " transition," because, as he thought, in their structure they exhibited
an intermediate character between Lehman's " primary" or metamorphic rocks, and the
" secondary" or fossilifcrous deposits. But the fossils peculiar to these beds having
been found in rocks without the transition structure, the name has long ago fallen into
disuse. The term " grauwacke" or " graywacke." a miners' term, was also introduced
from the Germans, and for some time employed to designate these rocks, because of the
nbundanoe in them of a compact argillaceous sandstone; but this awkward name has
also given place to Silurian, a term" introduced by sir R. I. Murchison when he first
established the system, and derived from the district where he investigated the strata,
which was the region of the Silures, a tribe of ancient Britons.

The Silurian system contains nn enormous thickness of rocks, nearly 30.000 ft.,
according to some estimates, the absolute thickness being greatly increased by immense
beds of intcrstratificd igneous rocks. The upper limit, underlying the old rVd sand-
stone, is universally accepted, but there has been considerable diversity of opinion in
regard to the inferior boundary. Prof. Scdgwiek, having described the rocks of n.
Wales, which at first were considered to be older than the series which Murchison had
illustrated, designated them Cambrian. This name has been retained for the immense
mass of indurated shales nnd sandstones of a thickness nearly equal to that of the
Silurians, which contain only faint traces of organic life, and "underlie the Llandeilo
formation. But Sedgwick claims also the lower Silurian rocks as a portion of his sys-
tem; the priority of name, and the uniform facies of the organic remains of the whole
of the Silurian rocks, have, however, induced geologists to consider the limits as origin-
ally given hv Murchison as those of the system.

The subdivisions of the rocks of the period arc the following:

UPPER SILURIAN ROCKS.

Thickness in Feet.
Upper Lvdlmf)

1. Downton Sandstone and Tilestoncs 80 to 1000

2. Upper Ludlow Shale 800

Lower Ludloif

3. Aymestry Limestone 150

4. Lower Ludlow Shale 900



Silurian.

Thickness in Feet.
Upper Wenlock

5. Wenlock Limestone 300

Lower Weidwk

6. Wenlock Shale 1400

7. \Yoolhope Limestone aad Denbighshire Grit 150

MIDDLE SILURIAN ROCKS.
Upper Llando'renj

8. Tarannon felmle v 1000

9. May- hill Sandstone and Pentamerous Limestone 800

Lower Llandovery

10. Lluudovery Slates 1000

LOWER SILURIAN ROCKS.
Caradoc

11. Caradoc Sandstone } 10 nnA

13. Bahi Limestone [ l ~'

Llandeilo

1'3. Upper Llandeilo )

14. Lower Llandeilo or Arenig Beds f

Contemporaneous Volcanic Rooks 5800

The typical Silurian strata arc in Wales, and the adjoining English county, Shrop-
shire. With the exception of the southern and south-eastern districts, where the old
red sandstone and coal measures occur, the whole of Wales is composed of Silurian and
Cambrian rocks. The same deposits are found in Cumberland and the n.of Lancashire.
The whole of Scotland, s. of a line drawn from Dunbar on the e. to Girvan on the w.,
consists of gray wacke rocks, slates, and limestones of Silurian age, with the exception
of one or two s-mall patches of old red, carboniferous, and permian strata. The rocks,
till recenth' referred loan azoic group, below the lowest fossiliferous strata in the n. of
Scotland, are now generally believed to be highly altered beds cf this period. The
Fouihern boundary of these beds is a line drawn from Stonehaven to Helensburgh. A
huge In. ugh, filled up with old red sandstone and carboniferous stiata, separates the
highly al'.ered strata cf the north from the less altered deposits of the south. An extensive
region of Silurian rocks occurs in the south-eastern counties of Ireland and in Gahvay;
and a great track of the same beds extends from the center of Ireland (Cavan, etc.) to
the coast of Down. The metamorphic rocks of the north-west are most probably also
of the same age as the corresponding strata in the n. of Scotland.

On the continent Silurian strata have been examined and corelated with the British
types, in Eohemia. by M. Tarrande; in Scandinavia, by M. Angelin; and in Russia by
jfurchison and others. In North America, also, extensive regions are covered with
1 'H>(! strata. They have been wrought out and their fossils described by the Canadian
r.nd United States surveyors. Similar strata have also been detected in India, Australia,
and South America. ,

The life of the period presents a group of very characteristic organism?, which, with
the exception of the fish-remains four. el in the upper beds, all belong to the iuverte-
brata. Many cf them are confined to the Silurian rocks, or occur only/very rarely in
some of the palaeozoic formations. The praptoliles are a strictly Silurian family of
zoophytes', and most of the forms of trilobiles are found only in this period, though
fome members of the tribe are found in rocks of Devonian and carboniferous age.
Besides these rray rlso be specified such forms as heliolites and favosites among the
con. Is; acti'" c -Suites anel the cystidians among the echinoderms; orthis and liugula
among the b a"hiopods: and lituites and maclurea among the cephalopoda.

In all the immense thickness of Silurian rocks no deposit has been discovered con-
taining organisms that have lived on land. Some fragments have been noticed that have
a faint resemblance to the branches of lepidodendron, anel minute bodies occur in the
bone-bed, which are referred to the spores of a terrestrial cryptogam. The only other
indications of plants are impressions believed to have been produced by sea-weeds.
The anthracitic shales of Wales and Scotland probably elerived their ! nthracite from the,
Igrc that must have abounded in the Silurian seas. In Shropshire a number of shells |
have been found, whose nearest allies are littoral species, and these r.ppe;-.r to indicate
the existence there of an ancient shore. The Silurian rocks a re, however, generally sea
deposits, and Forbes has ingeniously shown, from the small size of the con(.hifera > , the
paucity of spiral univalves, the great number of floating shells anel of the pelagic
orithidfo. and the great raritv, or absence except in the upper beds, of fossil fish, that it
is most probable they were deposited, in a sea more than 70 fathoms deep.

SILURIAN ROCKS (ante). The lower Silurian in North America embrace, I. the
primordial, or Cambrian period, which again embraces the Acadian and the Potsdam
epochs. II. Canadian period, which embraces the calciferous, the Quebec, and the
Chazy epochs. III. Trenton period, embracing the Trenton, Utica, and Hudson river
epochs. The upper Silurian embraces, 1. the Niagara period, with Medina, Clinton, and



Siluridae.
Silver.

Niagara epochs. 2. Salina period, containing the Onondnga salt group. 3. Lower
Hclderberg period, contaiuing the lower Helderberg limestone which includes In -New-
York, the water lime group, the lower pentamerous limestone, the ilelthrys shaly lime-
stone, and tlie upper peutamerous limestone. 4. Oriskany period, containing the Oria-
kany sandstone.

In the Acadian epoch the rocks are exposed to view in valleys in New Brunswick.
They are gray and black shales with some sandstones, and have a thickness of 2,000 feet.
In tlio Potsdam epoch in Labrador and Newfoundland are strata of limestones, sand-
stones, and shales from 5,000 to 5,600 ft. thick. In New York, Vermont, and Canada,
rocks, lying upon the Archean, are hard sandstones, sometimes pebbly conglomerates.
The sandstones are laminated, gray, drab, yellowish, brown, and red, often good build-
ing stone, as at Potsdam and Maloue. In Clinton and St. Lawrem e the conglomerate
. is often 300 ft. thick. In western Vermont there is red sandrock and AVino >ski lime-
stone. Along the Appalachians the striking characteristic is the great thickness of the
formation. In Pennsylvania there are in the primal series of Rogers 2,000 ft. of lower slates



dence only of marine life. The plants are chiefly fucoids. The animals are all inverte-
brates, as crinoids, brachiopods, pteropods, gasteropods, and cephalopods, worms and
crustaceans, including trilobites (q.v.).

The rocks of the Canadian period appear at the surface in northern New York,
Canada, northern Michigan, and Wisconsin; also in the Green mountains, the eastern
Appalachians, from New Jersey southward, and in Missouri, Arkansas, and the Kocky
mountains. The fossil flora and fauna of the Canadian period much resemble that of
the primordial, but are more particularly rich in graptolites (q.v.). The earlier part of
the Trenton period was particularly limestone-making. A broad belt of limestone of
this period extends from eastern New York to Wisconsin, Minnesota, and Missouri,
including the Galena limestone. It forms the bluffs at Trenton falls. The general
thickness is from lOO to 500 ft., reaching 1000, and in Pennsylvania, 2,000 feet. The
Utica shale comes to the surface in the Mohawk valley. Sea weeds are the only known
fossil plants. Among the radiates are crinoids and star fish, corals made their first
appearance. Various mollusks were numerous, and among crustaceans trilobites -were
abundant. The strata are much upturned, some of them having a vertical position,
others inclining from 10 to 90, the greater part between 30 and 60.

In the upper Silurian, the Niagara period contains Oneida conglomerates, in Oneida
cr>., N. Y., the lower member of the Medina epoch, the upper being Medina sandstone.
The conglomerate is 500 ft. thick in the Shawangunk mountains, where it is called
Shawangunk grit. The rocks of the Niagara epoch are very extensive, occupying a
large portion of the interior of the continent, and they are to a great extent limestones,
this being also a limestone-making epoch. Near Niagara falls there are 165 ft. of lime-
stone resting on 80 ft. of shale, and at the falls 85 ft. of limestone resting on 80 ft. of shale.
Along the Appalachians the rocks have a thickness of 1500 feet. Niagara limestone
occurs on the shores of Wellington and Barrow's straits and on King William's island,
and common chain coral has been found in the Arctic regions. There is lead anrl cop-
per in the Shawangunk grit in Ulster co. N. Y.,and these metels are found in other
Silurian rocks. Petroleum occurs in large quantities in Niagara limestone at Chicago,
111., but is not easily worked. The orfly fossil plants are sea weeds. As to animals the
sandstones of the Medina and Clinton groups contain the remains of many brachiopods
and lamellibranchs, but only a few corals and crinoids. The Clinton and Niagara limit-
ttone*, however, are rich in corals, crinoids, trilobites, and brachiopods. while there are
but few lamellibranchs or muddy bottom mollusks. The fine sandy and clayey charac-
ter of the Medina beds shows that at the time of their deposition central New York was
an extensive area of low, sandy sea shores, flats and marshes, not exposed to heavy
waves, and that a similar condition extended westward to Michigan. The beds of the
Niagara epoch bear evidence of having been formed in deep seas, from the thickness of
the limestones in the Mississippi basin and elsewhere. After the elevation of the Green,
mountains, according to Dana, there was a gradual sinking which moved the coast line
eastward to the Hudson, so that over New York and the interior basin there was a vast
limestone-making sea. At the same time there was another large sea in the St. Lawrence
region. In the course of these oscillations, from the beginning of the Trenton to the
close of the Niagara period there was a deposition of 12,000 ft. of rock along the Alle-
ghanies.

SILTJ RID 55, a family of malacopterous fishes, divided into many genera, and includ'
ing a great number of species, mostly inhabitants of the lakes and rivers of warm coun-
tries. The siluridre exhibit great diversity of form. Their skin is generally naked, but
some have a row of bony plates along the lateral line, and a few are completely mailed
with bony plates. The dorsal fin is single in some; others have two dorsal fins, thf sec-
ond being sometimes adipose, as in the salmon family. The dorsal fin is sometimes
armed with a strong spinous ray, and in most of the family the first ray of the pectoral
tins is very strong and serrated, so as to be capable of inflicting a severe wound, and by



KA'7 SUnridee.

OU Silver.

this these fishes are protected from alligators and other enemies. All have the mouth
furnished with barbels, more or less numerous; the two principal barbels being on the
upper lip, and formed by elongation of the intermaxillary bones. The barbels are
believed to be organs of touch, probably of use in directing the tish to its prey. The
bones of the head and other parts of the skeleton exhibit many peculiarities, into which,
we cannot enter. The siluridSB are generally inhabitants of muddy rivers, linking among
the mud. The only European species is the SLY SILURUS, SHEAT-FISH, or BHADSR
(siluriin fjltiuif-), the largest of European fresh-water fishes, and sometimes found in the
sea near the mouths of rivers. It does not inhabit any of the rivers of Britain; its intro-
duction has, however, recently been attempted. Neither is it found in France, Spain, or
Italy, but it is plentiful in the Danube, the Elbe, and their larger tributaries, also in ihe
rivers which fall into the Caspian sea; and it is found in some of the rivers of North
America. It attains a length of six or even eight feet, and a weight of ;JOO or 400 pounds.
The flesh is white and fat, but soft, luscious, and not very easily digestible. In t,he
northern countries of Europe it is preserved by drying, and the fat is used as Ir.rd. The
habits of the fish are sluggish It seems rathtr to lie in wait for its prey than to go in
quest of it. Several species of this family are found in the Nile, among which is the
H.UIMOUTH or KAKMOOT (cluri<i* angufllaris), 6 tish in its general form and appearance
much resembling that just described. It was anciently an object of supersli'iious regard
in the Thebaid.

SIL'VAS. or SELVAS (Span, selta. a forest), the name given to the western portion of
the great plain of the Amazon, in the n.w. of Brazil. The silvas, which are about one-
third of the whole plain, contain more than 700,000 English sq.m., and consist of low
land mi a dead level, densely covered wilh primeval forests, and annually inundated by
the overflow of the mighty river or its tributaries. The forests are rendered wholly
impenetrable from the denseness of the underwood, matted together as it is by creeping
and climbing plants which form myriads of festoons glowing with nature's brightest
tints. The vegetation of the silvas, under the stimulating action of the abundant irriga-
tion, the intense tropical heat, and the inconceivable richness of the alluvium which con-
stitutes the soil, shows an exuberance of growth far surpassing that of any oilier portion
of the earth's surface, and from its very luxuriance presents a bar to civilization no less
effectual than do the barren deserts of Africa or the gloomy wastes of central Asia.
The few Europeans who have penetrated into this region have sailed up the Amazon and
some of its tributaries, and from them we have received the little knowledge that we do
possess of this immense tract of wild forest. It is the haunt of innumerable wild animals,
especially monkeys and serpents, and of a few aboriginal inhabitants who are sunk in the
lowest stage of barbarism.

SILVER (symb. Ag, equiv. 108, pp. gr. 10.T3) is a metal which, in its compact state,
is of a brilliant white color, possesses the metallic luster to a remarkable degree, is capa-
ble of being highly polished, and evolves a clear ringing sound when struck. It is
harder than srold, but softer than copper, and is one of the most ductile nf the metals.
It is malleable, may be Irimmered into very thin leaves, and maybe drawn out into very
fine wire, the thinnest silver-leaf having a thickness of only TWCTRV f :in inch, and
one grain of the metal being capable of yielding 400 feet of wire. It possesses a high
degree of tenacity, a wire with a diameter of -^ of an inch being able to support a
weight of nearly 188 pounds. It requires a heal of 1873" Fahr. to fuse it, and on cool-
ing expands at the moment of solidification. It is an excellent conductor of heat and
electricitv. and is not affected by exposure, even to a moist atmosphere at any tempera-
ture. When, however, it is fused it absorbs a considerable quantity of oxygen which it
expels in the act of solidification with a peculiar sound technically known as spittinfj.*
But although it does not rust or become oxidized it usually becomes tarnished on pro-
longed exposure to the air. owing to the formation of a tilm of sulphide (or sulphuret)
of silver, and this change occurs more rapidlv in towns than in Ihe country in consequence
of sulphureted hydrogen being more abundant in the atmosphere of t'he former than of
the latter. This metal is unaffected by the hydrates or nitrates of the alkalies, even at a
high temperature, and hence silver crucibles, etc., are highly useful in many laboratory
operations.

Hydrochloric and dilute sulphuric acid have scarcely any action on silver, but nitric
acid and boiling sulphuric acid oxidize it. and form salts; nitric acid being by far its best
solvent. Silver has strong affinities for chlorine, bromine, iodine, and sulphur, and
combines with the first three and sulphureted hydrogen at ordinary temperatures. It
Is well known that common salt, especially in the melted state, when left for any time in
contact with silver, corrodes that metal, soda being formed from the oxygen of the air,
while the liberated chlorine attacks the silver.

Silver is frequently met with in the native state crystallized in cubes or octahedrons,
or occurring in fibrous masses. It is also found in combination with gold, mercury, lead,
antimony, arsenic, sulphur, etc., and sulphide of lead is almost always accompanied
with a greater or less amount of sulphide of silver; it is, however, never found as an
oxido.

Silver forms three compounds with oxygen viz., a suboxide, Ag a O; an oxide,

* Although ordinary air has no oxidizing action on silver, ozonized air rapidly attacks it.



Silver.



5C8



AgO; and a peroxide, AgO 2 . All these oxides possess the common properties of being
reduced by beat to tbe metallic state, and of being very readily decomposed by the actiou
of light. The oxido, Ag() ; is the only one of these compounds requiring sj e.vial notice.
It is a dark-bro\vi) heavy powder, devoid of taste or smell, somewhat soluble ia water, to
which ii communicates a metallic taste and an alkaline reaction. It acts as a powerful base,
neutralizing the strongest acids, and forming normal salts with them. It is obtained by
the addition of a solution of potash to a solution of the nitrate or any other soluble salt
of silver, falling as a hydraled oxide, which, at a temperature above 140 3 , becomes
anhydrous. If u concentrated solution of ammonia be digested for some hours upon
freshly precipitated oxide of silver, fulminate of silver (q.v.), or fulminating silver in
the form of a black powder is produced, and the same dangerous compound is formed
when an atnmoniacal solution of nitrate or chloride of silver is precipitated by potash.

The salts which the oxide of silver'forms with acids are characterized by the readi-
ness with which they decompose, the mere action of light blackening and partially
reducing them. None of these salts occur in nature. Tbe following are the most
important of ihose which have been formed artificially:

Hitrate of Silver (AgO,NO&) crystallizes in large, colorless, transparent square tablets,
which blacken on exposure to light, or in contact with organic matters, owing to reduc-
tion, and dissolve in their own weight of cold water. This properly of producing a per-
manent black color with organic matters has led to itymployment as a intirkinr/ ink* for
linen, etc. The black stains which it forms on the sKin, on linen, etc., may be removed
by the employment of a strong solution of iodide of potassium, or more readily by a
solution ot cyanide of potassium. The crystals fuse at attmperature of about 425, and
tbe molten mass, when cast into cylindrical molds, solidifies, and forms the sticks of
lunar caustic which are employed in surgery, medicine, and photography (q.v.). Nitrate
of silver is prepared by dissolving pure silver in moderately strong nitric acid, and
evaporating till the solution is sufficiently concentrated to crystallize. "The most char-
acteristic test for the salts of silver is the action of hydrochloric acid, or of a soluble
chloride, \\hich produces a white curdy precipitate of chloride of silver, insoluble in
nitric acid, but readily soluble in ammonia; it is also soluble in hyposulphite of soda,
with which it forms an intensely sweet solution; cyanide of potassium ah-o dissolves it;
the chloride of silver speedily assumes a violet tinge when exposed to light." Miller's
JUments of Uicmixtry, 2d ed., vol. ii. p. 732.

Of the haloid salts of silver, several occur native. The most important of these
compounds is chloride of silver (AgCl), which is found native either in cubes or in a dense
semi-transparent mass, and is known as lorn silrer, and may be procured as a dense
white flocculent precipitate by the procedure described in the preceding paragraph.
In consequence of its sensibility to light, it is employed in photography. When heated
to about 500, it fuses into a yellow fluid, which, on cooling, solidifies into a yellowish-
gray semi-transparent horny mass. This salt is insoluble in water and in all the diluted
acids, but dissolves in a solution of ammonia, from which it crystallizes in c.ctahedra.



Online LibraryFrancis LieberLibrary of universal knowledge. A reprint of the last (1880) Edinburgh and London edition of Chambers' encyclopaedia, with copious additions by American editors (Volume 13) → online text (page 117 of 203)