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<p><b>The Student’s Elements of Geology</b></p>
<hr>
<p class="page"><a name="page 35">[ 35 ]</a></p>
<p> </p>
<center><b>Chapter II</b><br>
<br>
AQUEOUS ROCKS.—THEIR COMPOSITION AND FORMS OF
STRATIFICATION.</center>
<p class="intro">Mineral Composition of Strata. — Siliceous
Rocks. — Argillaceous. — Calcareous. — Gypsum. — Forms of Stratification. — Original Horizontality. — Thinning
out. — Diagonal Arrangement. — Ripple-mark.</p>
<p>In pursuance of the arrangement explained in the last chapter,
we shall begin by examining the aqueous or sedimentary rocks, which
are for the most part distinctly stratified, and contain fossils.
We may first study them with reference to their mineral
composition, external appearance, position, mode of origin, organic
contents, and other characters which belong to them as aqueous
formations, independently of their age, and we may afterwards
consider them chronologically or with reference to the successive
geological periods when they originated.</p>
<p>I have already given an outline of the data which led to the
belief that the stratified and fossiliferous rocks were originally
deposited under water; but, before entering into a more detailed
investigation, it will be desirable to say something of the
ordinary materials of which such strata are composed. These may be
said to belong principally to three divisions, the siliceous, the
argillaceous, and the calcareous, which are formed respectively of
flint, clay, and carbonate of lime. Of these, the siliceous are
chiefly made up of sand or flinty grains; the argillaceous, or
clayey, of a mixture of siliceous matter with a certain proportion,
about a fourth in weight, of aluminous earth; and, lastly, the
calcareous rocks, or limestones, of carbonic acid and lime.</p>
<p>
<b>Siliceous and Arenaceous
Rocks.</b>—To speak first of the sandy division: beds
of loose sand are frequently met with, of which the grains consist
entirely of silex, which term comprehends all purely siliceous
minerals, as quartz and common flint. Quartz is silex in its purest
form. Flint usually contains some admixture of alumina and oxide of
iron. The siliceous grains in sand are usually rounded, as if by
the action of running water. Sandstone is an aggregate of such
grains, which often cohere together without any visible cement, but
more commonly are bound together</p>
<p> </p>
<hr>
<p class="page"><a name="page 36">[ 36 ]</a></p>
<br>
<p>by a slight quantity of siliceous or calcareous matter, or by
oxide of iron or clay.</p>
<p>Pure siliceous rocks may be known by not effervescing when a
drop of nitric, sulphuric or other acid is applied to them, or by
the grains not being readily scratched or broken by ordinary
pressure. In nature there is every intermediate gradation, from
perfectly loose sand to the hardest sandstone. In <i>micaceous
sandstones</i> mica is very abundant; and the thin silvery plates
into which that mineral divides are often arranged in layers
parallel to the planes of stratification, giving a slaty or
laminated texture to the rock.</p>
<p>When sandstone is coarse-grained, it is usually called <i>
grit.</i> If the grains are rounded, and large enough to be called
pebbles, it becomes a <i>conglomerate</i> or <i>pudding-stone,</i>
which may consist of pieces of one or of many different kinds of
rock. A conglomerate, therefore, is simply gravel bound together by
cement.</p>
<p><b>Argillaceous Rocks.</b>—Clay,
strictly speaking, is a mixture of silex or flint with a large
proportion, usually about one fourth, of alumina, or argil; but in
common language, any earth which possesses sufficient ductility,
when kneaded up with water, to be fashioned like paste by the hand,
or by the potter’s lathe, is called a <i>clay</i>; and such clays
vary greatly in their composition, and are, in general, nothing
more than mud derived from the decomposition or wearing down of
rocks. The purest clay found in nature is porcelain clay, or
kaolin, which results from the decomposition of a rock composed of
feldspar and quartz, and it is almost always mixed with quartz. The
kaolin of China consists of 71·15 parts of silex,
15·86 of alumine, 1·92 of lime, and 6·73 of
water;* but other porcelain clays differ materially, that of
Cornwall being composed, according to Boase, of nearly equal parts
of silica and alumine, with 1 per cent of magnesia.† <i>
Shale</i> has also the property, like clay, of becoming plastic in
water: it is a more solid form of clay, or argillaceous matter,
condensed by pressure. It always divides into laminæ more or
less regular.</p>
<p>One general character of all argillaceous rocks is to give out a
peculiar, earthy odour when breathed upon, which is a test of the
presence of alumine, although it does not belong to pure alumine,
but, apparently, to the combination of that substance with oxide of
iron.‡</p>
<p><b>Calcareous Rocks.</b>—This
division comprehends those rocks which, like chalk, are composed
chiefly of lime and carbonic</p>
<p class="fnote">* W. Phillips, Mineralogy, p.33.<br>
† Phil. Mag., vol. x, 1837.<br>
‡ See W. Phillips’s Mineralogy, “Alumine.”</p>
<p> </p>
<hr>
<p class="page"><a name="page 37">[ 37 ]</a></p>
<br>
<p>acid. Shells and corals are also formed of the same elements,
with the addition of animal matter. To obtain pure lime it is
necessary to calcine these calcareous substances, that is to say,
to expose them to heat of sufficient intensity to drive off the
carbonic acid, and other volatile matter. White chalk is sometimes
pure carbonate of lime; and this rock, although usually in a soft
and earthy state, is occasionally sufficiently solid to be used for
building, and even passes into a <i>compact</i> stone, or a stone
of which the separate parts are so minute as not to be
distinguishable from each other by the naked eye.</p>
<p>Many limestones are made up entirely of minute fragments of
shells and coral, or of calcareous sand cemented together. These
last might be called “calcareous sandstones;” but that term is more
properly applied to a rock in which the grains are partly
calcareous and partly siliceous, or to quartzose sandstones, having
a cement of carbonate of lime.</p>
<p>The variety of limestone called <i>oolite</i> is composed of
numerous small egg-like grains, resembling the roe of a fish, each
of which has usually a small fragment of sand as a nucleus, around
which concentric layers of calcareous matter have accumulated.</p>
<p>Any limestone which is sufficiently hard to take a fine polish
is called <i>marble.</i> Many of these are fossiliferous; but
statuary marble, which is also called saccharoid limestone, as
having a texture resembling that of loaf-sugar, is devoid of
fossils, and is in many cases a member of the metamorphic
series.</p>
<p><i>Siliceous limestone</i> is an intimate mixture of carbonate
of lime and flint, and is harder in proportion as the flinty matter
predominates.</p>
<p>The presence of carbonate of lime in a rock may be ascertained
by applying to the surface a small drop of diluted sulphuric,
nitric, or muriatic acid, or strong vinegar; for the lime, having a
greater chemical affinity for any one of these acids than for the
carbonic, unites immediately with them to form new compounds,
thereby becoming a sulphate, nitrate or muriate of lime. The
carbonic acid, when thus liberated from its union with the lime,
escapes in a gaseous form, and froths up or effervesces as it makes
its way in small bubbles through the drop of liquid. This
effervescence is brisk or feeble in proportion as the limestone is
pure or impure, or, in other words, according to the quantity of
foreign matter mixed with the carbonate of lime. Without the aid of
this test, the most experienced eye can not always detect the
presence of carbonate of lime in rocks.</p>
<p> </p>
<hr>
<p class="page"><a name="page 38">[ 38 ]</a></p>
<br>
<p>The above-mentioned three classes of rocks, the siliceous,
argillaceous, and calcareous, pass continually into each other, and
rarely occur in a perfectly separate and pure form. Thus it is an
exception to the general rule to meet with a limestone as pure as
ordinary white chalk, or with clay as aluminous as that used in
Cornwall for porcelain, or with sand so entirely composed of
siliceous grains as the white sand of Alum Bay, in the Isle of
Wight, employed in the manufacture of glass, or sandstone so pure
as the grit of Fontainebleau, used for pavement in France. More
commonly we find sand and clay, or clay and marl, intermixed in the
same mass. When the sand and clay are each in considerable
quantity, the mixture is called <i>loam.</i> If there is much
calcareous matter in clay it is called <i>marl</i>; but this term
has unfortunately been used so vaguely, as often to be very
ambiguous. It has been applied to substances in which there is no
lime; as, to that red loam usually called red marl in certain parts
of England. Agriculturists were in the habit of calling any soil a
marl which, like true marl, fell to pieces readily on exposure to
the air. Hence arose the confusion of using this name for soils
which, consisting of loam, were easily worked by the plough, though
devoid of lime.</p>
<p><i>Marl slate</i> bears the same relation to marl which shale
bears to clay, being a calcareous shale. It is very abundant in
some countries, as in the Swiss Alps. Argillaceous or marly
limestone is also of common occurrence.</p>
<p>There are few other kinds of rock which enter so largely into
the composition of sedimentary strata as to make it necessary to
dwell here on their characters. I may, however, mention two
others—magnesian limestone or dolomite, and gypsum. <i>Magnesian
limestone</i> is composed of carbonate of lime and carbonate of
magnesia; the proportion of the latter amounting in some cases to
nearly one half. It effervesces much more slowly and feebly with
acids than common limestone. In England this rock is generally of a
yellowish colour; but it varies greatly in mineralogical character,
passing from an earthy state to a white compact stone of great
hardness. <i>Dolomite,</i> so common in many parts of Germany and
France, is also a variety of magnesian limestone, usually of a
granular texture.</p>
<p><i>Gypsum</i> is a rock composed of sulphuric acid, lime, and
water. It is usually a soft whitish-yellow rock, with a texture
resembling that of loaf-sugar, but sometimes it is entirely
composed of lenticular crystals. It is insoluble in acids, and does
not effervesce like chalk and dolomite, because it does not contain
carbonic acid gas, or fixed air, the lime</p>
<p> </p>
<hr>
<p class="page"><a name="page 39">[ 39 ]</a></p>
<br>
<p>being already combined with sulphuric acid, for which it has a
stronger affinity than for any other. Anhydrous gypsum is a rare
variety, into which water does not enter as a component part. <i>
Gypseous marl</i> is a mixture of gypsum and marl. <i>Alabaster</i>
is a granular and compact variety of gypsum found in masses large
enough to be used in sculpture and architecture. It is sometimes a
pure snow-white substance, as that of Volterra in Tuscany, well
known as being carved for works of art in Florence and Leghorn. It
is a softer stone than marble, and more easily wrought.</p>
<p><b>Forms of
Stratification.</b>—A series of strata sometimes
consists of one of the above rocks, sometimes of two or more in
alternating beds.</p>
<p>Thus, in the coal districts of England, for example, we often
pass through several beds of sandstone, some of finer, others of
coarser grain, some white, others of a dark colour, and below
these, layers of shale and sandstone or beds of shale, divisible
into leaf-like laminæ, and containing beautiful impressions
of plants. Then again we meet with beds of pure and impure coal,
alternating with shales and sandstones, and underneath the whole,
perhaps, are calcareous strata, or beds of limestone, filled with
corals and marine shells, each bed distinguishable from another by
certain fossils, or by the abundance of particular species of
shells or zoophytes.</p>
<p>This alternation of different kinds of rock produces the most
distinct stratification; and we often find beds of limestone and
marl, conglomerate and sandstone, sand and clay, recurring again
and again, in nearly regular order, throughout a series of many
hundred strata. The causes which may produce these phenomena are
various, and have been fully discussed in my treatise on the modern
changes of the earth’s surface.* It is there seen that rivers
flowing into lakes and seas are charged with sediment, varying in
quantity, composition, colour, and grain according to the seasons;
the waters are sometimes flooded and rapid, at other periods low
and feeble; different tributaries, also, draining peculiar
countries and soils, and therefore charged with peculiar sediment,
are swollen at distinct periods. It was also shown that the waves
of the sea and currents undermine the cliffs during wintry storms,
and sweep away the materials into the deep, after which a season of
tranquillity succeeds, when nothing but the finest mud is spread by
the movements of the ocean over the same submarine area.</p>
<p>It is not the object of the present work to give a
description</p>
<p class="fnote">* Consult Index to Principles of Geology,
“Stratification,” “Currents,” “Deltas,” “Water,” etc.</p>
<p> </p>
<hr>
<p class="page"><a name="page 40">[ 40 ]</a></p>
<br>
<p>of these operations, repeated as they are, year after year, and
century after century; but I may suggest an explanation of the
manner in which some micaceous sandstones have originated, namely,
those in which we see innumerable thin layers of mica dividing
layers of fine quartzose sand. I observed the same arrangement of
materials in recent mud deposited in the estuary of Laroche St.
Bernard in Brittany, at the mouth of the Loire. The surrounding
rocks are of gneiss, which, by its waste, supplies the mud: when
this dries at low water, it is found to consist of brown laminated
clay, divided by thin seams of mica. The separation of the mica in
this case, or in that of micaceous sandstones, may be thus
understood. If we take a handful of quartzose sand, mixed with
mica, and throw it into a clear running stream, we see the
materials immediately sorted by the water, the grains of quartz
falling almost directly to the bottom, while the plates of mica
take a much longer time to reach the bottom, and are carried
farther down the stream. At the first instant the water is turbid,
but immediately after the flat surfaces of the plates of mica are
seen all alone, reflecting a silvery light, as they descend slowly,
to form a distinct micaceous lamina. The mica is the heavier
mineral of the two; but it remains a longer time suspended in the
fluid, owing to its greater extent of surface. It is easy,
therefore, to perceive that where such mud is acted upon by a river
or tidal current, the thin plates of mica will be carried farther,
and not deposited in the same places as the grains of quartz; and
since the force and velocity of the stream varies from time to
time, layers of mica or of sand will be thrown down successively on
the same area.</p>
<p><b>Original
Horizontality.</b>—It is said generally that the upper
and under surfaces of strata, or the “planes of stratification,”
are parallel. Although this is not strictly true, they make an
approach to parallelism, for the same reason that sediment is
usually deposited at first in nearly horizontal layers. Such an
arrangement can by no means be attributed to an original evenness
or horizontality in the bed of the sea: for it is ascertained that
in those places where no matter has been recently deposited, the
bottom of the ocean is often as uneven as that of the dry land,
having in like manner its hills, valleys, and ravines. Yet if the
sea should go down, or be removed from near the mouth of a large
river where a delta has been forming, we should see extensive
plains of mud and sand laid dry, which, to the eye, would appear
perfectly level, although, in reality, they would slope gently from
the land towards the sea.</p>
<p> </p>
<hr>
<p class="page"><a name="page 41">[ 41 ]</a></p>
<br>
<p>This tendency in newly-formed strata to assume a horizontal
position arises principally from the motion of the water, which
forces along particles of sand or mud at the bottom, and causes
them to settle in hollows or depressions where they are less
exposed to the force of a current than when they are resting on
elevated points. The velocity of the current and the motion of the
superficial waves diminish from the surface downward, and are least
in those depressions where the water is deepest.</p>
<img src="../images/fig1.jpg" width="175" height="73" align="right"
alt="Fig. 1">
<p>A good illustration of the principle here alluded to may be
sometimes seen in the neighbourhood of a volcano, when a section,
whether natural or artificial, has laid open to view a succession
of various-coloured layers of sand and ashes, which have fallen in
showers upon uneven ground. Thus let A B (Fig. 1) be two ridges,
with an intervening valley. These original inequalities of the
surface have been gradually effaced by beds of sand and ashes <i>c,
d, e,</i> the surface at <i>e</i> being quite level. It will be
seen that, although the materials of the first layers have
accommodated themselves in a great degree to the shape of the
ground A B, yet each bed is thickest at the bottom. At first a
great many particles would be carried by their own gravity down the
steep sides of A and B, and others would afterwards be blown by the
wind as they fell off the ridges, and would settle in the hollow,
which would thus become more and more effaced as the strata
accumulated from <i>c</i> to <i>e.</i> Now, water in motion can
exert this levelling power on similar materials more easily than
air, for almost all stones lose in water more than a third of the
weight which they have in air, the specific gravity of rocks being
in general as 2½ when compared to that of water, which is
estimated at 1. But the buoyancy of sand or mud would be still
greater in the sea, as the density of salt-water exceeds that of
fresh.</p>
<center><img src="../images/fig2.jpg" width="336" height="100" alt=
"Fig. 2. Section of strata of sandtone, grit, and congolmerate.">
</center>
<p>Yet, however uniform and horizontal may be the surface of new
deposits in general, there are still many disturbing causes, such
as eddies in the water, and currents moving first in one and then
in another direction, which frequently cause</p>
<p> </p>
<hr>
<p class="page"><a name="page 42">[ 42 ]</a></p>
<br>
<p>irregularities. We may sometimes follow a bed of limestone,
shale, or sandstone, for a distance of many hundred yards
continuously; but we generally find at length that each individual
stratum thins out, and allows the beds which were previously above
and below it to meet. If the materials are coarse, as in grits and
conglomerates, the same beds can rarely be traced many yards
without varying in size, and often coming to an end abruptly. (See
Fig. 2.)</p>
<center><img src="../images/fig3.jpg" width="307" height="307" alt=
"Fig. 3: Section of sand at Sandy Hill, near Biggleswade, Bedfordshire.">
</center>
<p><b>Diagonal or Cross
Stratification.</b>—There is also another phenomenon
of frequent occurrence. We find a series of larger strata, each of
which is composed of a number of minor layers placed obliquely to
the general planes of stratification. To this diagonal arrangement
the name of “false or cross bedding” has been given. Thus in the
section (Fig. 3) we see seven or eight large beds of loose sand,
yellow and brown, and the lines <i>a, b, c</i> mark some of the
principal planes of stratification, which are nearly horizontal.
But the greater part of the subordinate laminæ do not conform
to these planes, but have often a steep slope, the inclination
being sometimes towards opposite points of the compass. When the
sand is loose and incoherent, as in the case here represented, the
deviation from parallelism of the slanting laminæ can not
possibly be accounted for by any rearrangement of the particles
acquired during the consolidation of the rock. In what manner,
then, can such irregularities be</p>
<p> </p>
<hr>
<p class="page"><a name="page 43">[ 43 ]</a></p>
<br>
<p>due to original deposition? We must suppose that at the bottom
of the sea, as well as in the beds of rivers, the motions of waves,
currents, and eddies often cause mud, sand, and gravel to be thrown
down in heaps on particular spots, instead of being spread out
uniformly over a wide area. Sometimes, when banks are thus formed,
currents may cut passages through them, just as a river forms its
bed.</p>
<center><img src="../images/fig4.jpg" width="338" height="114" alt=
"Fig. 4"><img src="../images/fig5.jpg" width="329" height="93" alt=
"Fig. 5"></center>
<p>Suppose the bank A (Fig. 4) to be thus formed with a steep
sloping side, and, the water being in a tranquil state, the layer
of sediment No. 1 is thrown down upon it, conforming nearly to its
surface. Afterwards the other layers, 2, 3, 4, may be deposited in
succession, so that the bank B C D is formed. If the current then
increases in velocity, it may cut away the upper portion of this
mass down to the dotted line e, and deposit the materials thus
removed farther on, so as to form the layers 5, 6, 7, 8. We have
now the bank B, C, D, E (Fig. 5), of which the surface is almost
level, and on which the nearly horizontal layers, 9, 10, 11, may
then accumulate. It was shown in Fig. 3 that the diagonal layers of
successive strata may sometimes have an opposite slope. This is
well seen in some cliffs of loose sand on the Suffolk coast. A
portion of one of these is represented in Fig. 6, where the layers,
of which there are about six in the thickness of an inch, are
composed of quartzose grains. This arrangement may have been due to
the altered direction of the tides and currents in the same
place.</p>
<center><img src="../images/fig6.jpg" width="213" height="129" alt=
"Fig. 6: Cliff between Mismer and Dunwich."></center>
<p> </p>
<hr>
<p class="page"><a name="page 44">[ 44 ]</a></p>
<br>
<center><img src="../images/fig7.jpg" width="367" height="206" alt=
"Fig. 7: Section from Monte Calvo to the sea by the valley of the Magnan, near Nice.">
</center>
<p>The description above given of the slanting position of the
minor layers constituting a single stratum is in certain cases
applicable on a much grander scale to masses several hundred feet
thick, and many miles in extent. A fine example may be seen at the
base of the Maritime Alps near Nice. The mountains here terminate
abruptly in the sea, so that a depth of one hundred fathoms is
often found within a stone’s throw of the beach, and sometimes a
depth of 3000 feet within half a mile. But at certain points,
strata of sand, marl, or conglomerate intervene between the shore
and the mountains, as in the section (Fig. 7), where a vast
succession of slanting beds of gravel and sand may be traced from
the sea to Monte Calvo, a distance of no less than nine miles in a
straight line. The dip of these beds is remarkably uniform, being
always southward or towards the Mediterranean, at an angle of about
25°. They are exposed to view in nearly vertical precipices,
varying from 200 to 600 feet in height, which bound the valley
through which the river Magnan flows. Although, in a general view,
the strata appear to be parallel and uniform, they are nevertheless
found, when examined closely, to be wedge-shaped, and to thin out
when followed for a few hundred feet or yards, so that we may
suppose them to have been thrown down originally upon the side of a
steep bank where a river or Alpine torrent discharged itself into a
deep and tranquil sea, and formed a delta, which advanced gradually
from the base of Monte Calvo to a distance of nine miles from the
original shore. If subsequently this part of the Alps and bed of
the sea were raised 700 feet, the delta may have emerged, a deep
channel may then have been cut through it by the river, and the
coast may at the same time have acquired its present
configuration.</p>
<p>It is well known that the torrents and streams which now</p>
<p> </p>
<hr>
<p class="page"><a name="page 45">[ 45 ]</a></p>
<br>
<p>descend from the Alpine declivities to the shore, bring down
annually, when the snow melts, vast quantities of shingle and sand,
and then, as they subside, fine mud, while in summer they are
nearly or entirely dry; so that it may be safely assumed that
deposits like those of the valley of the Magnan, consisting of
coarse gravel alternating with fine sediment, are still in progress
at many points, as, for instance, at the mouth of the Var. They
must advance upon the Mediterranean in the form of great shoals
terminating in a steep talus; such being the original mode of
accumulation of all coarse materials conveyed into deep water,
especially where they are composed in great part of pebbles, which
can not be transported to indefinite distances by currents of
moderate velocity. By inattention to facts and inferences of this
kind, a very exaggerated estimate has sometimes been made of the
supposed depth of the ancient ocean. There can be no doubt, for
example, that the strata <i>a</i>, Fig. 7, or those nearest to
Monte Calvo, are older than those indicated by <i>b</i>, and these
again were formed before <i>c</i>; but the vertical depth of gravel
and sand in any one place can not be proved to amount even to 1000
feet, although it may perhaps be much greater, yet probably never
exceeding at any point 3000 or 4000 feet. But were we to assume
that all the strata were once horizontal, and that their present
dip or inclination was due to subsequent movements, we should then
be forced to conclude that a sea several miles deep had been filled
up with alternate layers of mud and pebbles thrown down one upon
another.</p>
<p> </p>
<hr>
<p class="page"><a name="page 46">[ 46 ]</a></p>
<br>
<br>
<br>
<p>In the locality now under consideration, situated a few miles to
the west of Nice, there are many geological data, the details of
which can not be given in this place, all leading to the opinion
that, when the deposit of the Magnan was formed, the shape and
outline of the Alpine declivities and the shore greatly resembled
what we now behold at many points in the neighbourhood. That the
beds <i>a, b, c, d</i> are of comparatively modern date is proved
by this fact, that in seams of loamy marl intervening between the
pebbly beds are fossil shells, half of which belong to species now
living in the Mediterranean.</p>
<center><img src="../images/fig8.jpg" width="295" height="261" alt=
"Fig. 8: Slab of ripple-marked (New Red) sandstone from Cheshire.">
</center>
<p><b>Ripple-mark.</b>—The
ripple-mark, so common on the surface of sandstones of all ages
(see Fig. 8), and which is so often seen on the sea-shore at low
tide, seems to originate in the drifting of materials along the
bottom of the water, in a manner very similar to that which may
explain the inclined layers above described. This ripple is not
entirely confined to the beach between high and low water mark, but
is also produced on sands which are constantly covered by water.
Similar undulating ridges and furrows may also be sometimes seen on
the surface of drift snow and blown sand.</p>
<p>The ripple-mark is usually an indication of a sea-beach, or of
water from six to ten feet deep, for the agitation caused by waves
even during storms extends to a very slight depth. To this rule,
however, there are some exceptions, and recent ripple-marks have
been observed at the depth of 60 or 70 feet. It has also been
ascertained that currents or large bodies of water in motion may
disturb mud and sand at the depth of 300 or even 450 feet.* Beach
ripple, however, may usually be distinguished from current ripple
by frequent changes in its direction. In a slab of sandstone, not
more than an inch thick, the furrows or ridges of an ancient ripple
may often be seen in several successive laminæ to run towards
different points of the compass.</p>
<p class="fnote">* Darwin, Volcanic Islands, p. 134.</p>
<br>
<hr>
<small><a href="contents.html">Contents</a> / <a href="ch1.html">
Chapter I</a> / <a href="ch3.html">Chapter III</a></small>
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