Chapter XII: Front Matter (12)

The invention, or at least the earliest general use of this form, is attributed to Edward Lear, who, when a tutor in the family of the earl of Derby at Knowsley, composed, about 1834, a large number of nonsense-limericks to amuse the little grandchildren of the house. Many of these he published, with illustrations, in 1846, and they enjoyed and still enjoy an extreme popularity. Lear preferred to give a geographical colour to his absurdities, as in:--

"There was an old person of Tartary
Who cut through his jugular artery,
When up came his wife,
And exclaimed, 'O my Life,
How your loss will be felt through all Tartary!'"

but this is by no means essential. The neatness of the form has led to a very extensive use of the limerick for all sorts of mock-serious purposes, political, social and sarcastic, and a good many specimens have achieved a popularity which has been all the wider because they have, perforce, been confined to verbal transmission. In recent years competitions of the "missing word" type have had considerable vogue, the competitor, for instance, having to supply the last line of the limerick.

LIMES GERMANICUS. The Latin noun _limes_ denoted generally a path, sometimes a boundary path (possibly its original sense) or boundary, and hence it was utilized by Latin writers occasionally to denote frontiers definitely delimited and marked in some distinct fashion. This latter sense has been adapted and extended by modern historians concerned with the frontiers of the Roman Empire. Thus the Wall of Hadrian in north England (see BRITAIN: _Roman_) is now sometimes styled the _Limes Britannicus_, the frontier of the Roman province of Arabia facing the desert the _Limes Arabicus_ and so forth. In particular the remarkable frontier lines which bounded the Roman provinces of Upper (southern) Germany and Raetia, and which at their greatest development stretched from near Bonn on the Rhine to near Regensburg on the Danube, are often called the _Limes Germanicus_. The history of these lines is the subject of the following paragraphs. They have in the last fifteen years become much better known through systematic excavations financed by the German empire and through other researches connected therewith, and though many important details are still doubtful, their general development can be traced.

From the death of Augustus (A.D. 14) till after A.D. 70 Rome accepted as her German frontier the water-boundary of the Rhine and upper Danube. Beyond these rivers she held only the fertile plain of Frankfort, opposite the Roman border fortress of Moguntiacum (Mainz), the southernmost slopes of the Black Forest and a few scattered têtes-du-pont. The northern section of this frontier, where the Rhine is deep and broad, remained the Roman boundary till the empire fell. The southern part was different. The upper Rhine and upper Danube are easily crossed. The frontier which they form is inconveniently long, enclosing an acute-angled wedge of foreign territory--the modern Baden and Württemberg. The German populations of these lands seem in Roman times to have been scanty, and Roman subjects from the modern Alsace and Lorraine had drifted across the river eastwards. The motives alike of geographical convenience and of the advantages to be gained by recognizing these movements of Roman subjects combined to urge a forward policy at Rome, and when the vigorous Vespasian had succeeded the fool-criminal Nero, a series of advances began which gradually closed up the acute angle, or at least rendered it obtuse.

The first advance came about 74, when what is now Baden was invaded and in part annexed and a road carried from the Roman base on the upper Rhine, Strassburg, to the Danube just above Ulm. The point of the angle was broken off. The second advance was made by Domitian about A.D. 83. He pushed out from Moguntiacum, extended the Roman territory east of it and enclosed the whole within a systematically delimited and defended frontier with numerous blockhouses along it and larger forts in the rear. Among the blockhouses was one which by various enlargements and refoundations grew into the well-known Saalburg fort on the Taunus near Homburg. This advance necessitated a third movement, the construction of a frontier connecting the annexations of A.D. 74 and 83. We know the line of this frontier which ran from the Main across the upland Odenwald to the upper waters of the Neckar and was defended by a chain of forts. We do not, however, know its date, save that, if not Domitian's work, it was carried out soon after his death, and the whole frontier thus constituted was reorganized, probably by Hadrian, with a continuous wooden palisade reaching from Rhine to Danube. The angle between the rivers was now almost full. But there remained further advance and further fortification. Either Hadrian or, more probably, his successor Pius pushed out from the Odenwald and the Danube, and marked out a new frontier roughly parallel to but in advance of these two lines, though sometimes, as on the Taunus, coinciding with the older line. This is the frontier which is now visible and visited by the curious. It consists, as we see it to-day, of two distinct frontier works, one, known as the Pfahlgraben, is an earthen mound and ditch, best seen in the neighbourhood of the Saalburg but once extending from the Rhine southwards into southern Germany. The other, which begins where the earthwork stops, is a wall, though not a very formidable wall, of stone, the Teufelsmauer; it runs roughly east and west parallel to the Danube, which it finally joins at Heinheim near Regensburg. The Pfahlgraben is remarkable for the extraordinary directness of its southern part, which for over 50 m. runs mathematically straight and points almost absolutely true for the Polar star. It is a clear case of an ancient frontier laid out in American fashion. This frontier remained for about 100 years, and no doubt in that long period much was done to it to which we cannot affix precise dates. We cannot even be absolutely certain when the frontier laid out by Pius was equipped with the Pfahlgraben and Teufelsmauer. But we know that the pressure of the barbarians began to be felt seriously in the later part of the 2nd century, and after long struggles the whole or almost the whole district east of Rhine and north of Danube was lost--seemingly all within one short period--about A.D. 250.

The best English account will be found in H. F. Pelham's essay in
_Trans. of the Royal Hist. Soc._ vol. 20, reprinted in his _Collected
Papers_, pp. 178-211 (Oxford, 1910), where the German authorities are
fully cited. (F. J. H.)

LIMESTONE, in petrography, a rock consisting essentially of carbonate of lime. The group includes many varieties, some of which are very distinct; but the whole group has certain properties in common, arising from the chemical composition and mineral character of its members. All limestones dissolve readily in cold dilute acids, giving off bubbles of carbonic acid. Citric or acetic acid will effect this change, though the mineral acids are more commonly employed. Limestones, when pure, are soft rocks readily scratched with a knife-blade or the edge of a coin, their hardness being 3; but unless they are earthy or incoherent, like chalk or sinter, they do not disintegrate by pressure with the fingers and cannot be scratched with the finger nail. When free from impurities limestones are white, but they generally contain small quantities of other minerals than calcite which affect their colour. Many limestones are yellowish or creamy, especially those which contain a little iron oxide, iron carbonate or clay. Others are bluish from the presence of iron sulphide, or pyrites or marcasite; or grey and black from admixture with carbonaceous or bituminous substances. Red limestones usually contain haematite; in green limestones there may be glauconite or chlorite. In crystalline limestones or marbles many silicates may occur producing varied colours, e.g. epidote, chlorite, augite (green); vesuvianite and garnet (brown and red); graphite, spinels (black and grey); epidote, chondrodite (yellow). The specific gravity of limestones ranges from 2.6 to 2.8 in typical examples.

When seen in the field, limestones are often recognizable by their method of weathering. If very pure, they may have smooth rounded surfaces, or may be covered with narrow runnels cut out by the rain. In such cases there is very little soil, and plants are found growing only in fissures or crevices where the insoluble impurities of the limestone have been deposited by the rain. The less pure rocks have often eroded or pitted surfaces, showing bands or patches rendered more resistant to the action of the weather by the presence of insoluble materials such as sand, clay or chert. These surfaces are often known from the crust of hydrous oxides of iron produced by the action of the atmosphere on any ferriferous ingredients of the rock; they are sometimes black when the limestone is carbonaceous; a thin layer of gritty sand grains may be left on the surface of limestones which are slightly arenaceous. Most limestones which contain fossils show these most clearly on weathered surfaces, and the appearance of fragments of corals, crinoids and shells on the exposed parts of a rock indicate a strong probability that that rock is a limestone. The interior usually shows the organic structures very imperfectly or not at all.

Another characteristic of pure limestones, where they occur in large masses occupying considerable areas, is the frequency with which they produce bare rocky ground, especially at high elevations, or yield only a thin scanty soil covered with short grass. In mountainous districts limestones are often recognizable by these peculiarities. The chalk downs are celebrated for the close green sward which they furnish. More impure limestones, like those of the Lias and Oolites, contain enough insoluble mineral matter to yield soils of great thickness and value, e.g. the Cornbrash. In limestone regions all waters tend to be hard, on account of the abundant carbonate of lime dissolved by percolating waters, and caves, swallow holes, sinks, pot-holes and underground rivers may occur in abundance. Some elevated tracts of limestone are very barren (e.g. the Causses), because the rain which falls in them sinks at once into the earth and passes underground. To a large extent this is true of the chalk downs, where surface waters are notably scarce, though at considerable depths the rocks hold large supplies of water.

The great majority of limestones are of organic formation, consisting
of the debris of the skeletons of animals. Some are foraminiferal,
others are crinoidal, shelly or coral limestones according to the
nature of the creatures whose remains they contain. Of foraminiferal
limestones chalk is probably the best known; it is fine, white and
rather soft, and is very largely made up of the shells of globigerina
and other foraminifera (see CHALK). Almost equally important are the
nummulitic limestones so well developed in Mediterranean countries
(Spain, France, the Alps, Greece, Algeria, Egypt, Asia Minor, &c.).
The pyramids of Egypt are built mainly of nummulitic limestone.
Nummulites are large cone-shaped foraminifera with many chambers
arranged in spiral order. In Britain the small globular shells of
_Saccamina_ are important constituents of some Carboniferous
limestones; but the upper portion of that formation in Russia, eastern
Asia and North America is characterized by the occurrence of
limestones filled with the spindle-shaped shells of _Fusulina_, a
genus of foraminifera now extinct.

Coral limestones are being formed at the present day over a large
extent of the tropical seas; many existing coral reefs must be of
great thickness. The same process has been going on actively since a
very early period of the earth's history, for similar rocks are found
in great abundance in many geological formations. Some Silurian
limestones are rich in corals; in the Devonian there are deposits
which have been described as coral reefs (Devonshire, Germany). The
Carboniferous limestone, or mountain limestones of England and North
America, is sometimes nearly entirely coralline, and the great
dolomite masses of the Trias in the eastern Alps are believed by many
to be merely altered coral reefs. A special feature of coral
limestones is that, although they may be to a considerable extent
dolomitized, they are generally very free from silt and mechanical
impurities.

Crinoidal limestones, though abundant among the older rocks, are not
in course of formation on any great scale at the present time, as
crinoids, formerly abundant, are now rare. Many Carboniferous and
Silurian limestones consist mainly of the little cylindrical joints of
these animals. They are easily recognized by their shape, and by the
fact that many of them show a tube along their axes, which is often
filled up by carbonate of lime; under the microscope they have a
punctate or fenestrate structure and each joint behaves as a simple
crystalline plate with uniform optical properties in polarized light.
Remains of other echinoderms (starfishes and sea urchins) are often
found in plenty in Secondary and Tertiary limestones, but very seldom
make up the greater part of the rock. Shelly limestones may consist of
mollusca or of brachiopoda, the former being common in limestones of
all ages while the latter attained their principal development in the
Palaeozoic epoch. The shells are often broken and may have been
reduced to shell sand before the rock consolidated. Many rocks of this
class are impure and pass into marls and shelly sandstones which were
deposited in shallow waters, where land-derived sediment mingled with
remains of the creatures which inhabited the water. Fresh-water
limestones are mostly of this class and contain shells of those
varieties of mollusca which inhabit lakes. Brackish water limestones
also are usually shelly. Corallines (bryozoa, polyzoa, &c.),
cephalopods (e.g. ammonites, belemnites), crustaceans and sponges
occur frequently in limestones. It should be understood that it is not
usual for a rock to be built up entirely of one kind of organism
though it is classified according to its most abundant or most
conspicuous ingredients.

In the organic limestones there usually occurs much finely granular
calcareous matter which has been described as limestone mud or
limestone paste. It is the finely ground substance which results from
the breaking down of shells, &c., by the waves and currents, and by
the decay which takes place in the sea bottom before the fragments are
compacted into hard rock. The skeletal parts of marine animals are not
always converted into limestone in the place where they were formed.
In shallow waters, such as are the favourite haunts of mollusca,
corals, &c., the tides and storms are frequently sufficiently powerful
to shift the loose material on the sea bottom. A large part of a coral
reef consists of broken coral rock dislodged from the growing mass and
carried upwards to the beach or into the lagoon. Large fragments also
fall over the steep outward slopes of the reef and build up a talus at
their base. Coral muds and coral sands produced by the waves acting in
these detached blocks, are believed to cover two and a half millions
of square miles of the ocean floor. Owing to the fragile nature of the
shells of foraminifera they readily become disintegrated, especially
at considerable depths, largely by the solvent action of carbonic acid
in sea water as they sink to the bottom. The chalk in very great part
consists not of entire shells but of debris of foraminifera, and
mollusca (such as _Inoceramus_, &c.). The Globigerina ooze is the most
widespread of modern calcareous formations. It occupies nearly fifty
millions of square miles of the sea bottom, at an average depth of two
thousand fathoms. Pteropod ooze, consisting mainly of the shells of
pteropods (mollusca) also has a wide distribution, especially in
northern latitudes.

Consolidation may to a considerable extent be produced by pressure,
but more commonly cementation and crystallization play a large part in
the process. Recent shell sands on beaches and in dunes are not
unfrequently converted into a soft, semi-coherent rock by rain water
filtering downwards, dissolving and redepositing carbonate of lime
between the sand grains. In coral reefs also the mass soon has its
cavities more or less obliterated by a deposit of calcite from
solution. The fine interstitial mud or paste presents a large surface
to the solvents, and is more readily attacked than the larger and more
compact shell fragments. In fresh-water marls considerable masses of
crystalline calcite may be produced in this way, enclosing
well-preserved molluscan shells. Many calcareous fragments consist of
aragonite, wholly or principally, and this mineral tends to be
replaced by calcite. The aragonite, as seen in sections under the
microscope, is usually fibrous or prismatic, the calcite is more
commonly granular with a well-marked network of rhombohedral cleavage
cracks. The replacement of aragonite by calcite goes on even in shells
lying on modern sea shores, and is often very complete in rocks
belonging to the older geological periods. By the recrystallization of
the finer paste and the introduction of calcite in solution the
interior of shells, corals, foraminifera, &c., becomes occupied by
crystalline calcite, sometimes in comparatively large grains, while
the original organic structures may be very well-preserved.

Some limestones are exceedingly pure, e.g. the chalk and some
varieties of mountain limestone, and these are especially suited for
making lime. The majority, however, contain admixture of other
substances, of which the commonest are clay and sand. Clayey or
argillaceous limestones frequently occur in thin or thick beds
alternating with shales, as in the Lias of England (the marlstone
series). Friable argillaceous fresh-water limestones are called
"marls," and are used in many districts for top dressing soils, but
the name "marl" is loosely applied and is often given to beds which
are not of this nature (e.g. the red marls of the Trias). The "cement
stones" of the Lothians in Scotland are argillaceous limestones of
Lower Carboniferous age, which when burnt yield cement. The gault
(Upper Cretaceous) is a calcareous clay, often containing
well-preserved fossils, which lies below the chalk and attains
considerable importance in the south-east of England. Arenaceous
limestones pass by gradual transitions into shelly sandstones; in the
latter the shells are often dissolved leaving cavities, which may be
occupied by casts. Some of the Old Red Sandstone is calcareous. In
other cases the calcareous matter has recrystallized in large plates
which have shining cleavage surfaces dotted over with grains of sand
(Lincolnshire limestone). The Fontainebleau sandstone has large
calcite rhombohedra filled with sand grains. Limestones sometimes
contain much plant matter which has been converted into a dark coaly
substance, in which the original woody structures may be preserved or
may not. The calcareous petrified plants of Fifeshire occur in such a
limestone, and much has been learned from a microscopic study of them
regarding the anatomy of the plants of the Carboniferous period.
Volcanic ashes occur in some limestones, a good example being the
calcareous schalsteins or tuffs of Devonshire, which are usually much
crushed by earth movements. In the Globigerina ooze of the present day
there is always a slight admixture of volcanic materials derived
either from wind-blown dust, from submarine eruptions or from floating
pieces of pumice. Other limestones contain organic matter in the shape
of asphalt, bitumen or petroleum, presumably derived from plant
remains. The well-known _Val de Travers_ is a bituminous limestone of
lower Neocomian age found in the valley of that name near Neuchâtel.
Some of the oil beds of North America are porous limestones, in the
cavities of which the oil is stored up. Siliceous limestones, where
their silica is original and of organic origin, have contained
skeletons of sponges or radiolaria. In the chalk the silica has
usually been dissolved and redeposited as flint nodules, and in the
Carboniferous limestone as chert bands. It may also be deposited in
the corals and other organic remains, silicifying them, with
preservation of the original structures (e.g. some Jurassic and
Carboniferous limestones).

The oolitic limestones form a special group distinguished by their
consisting of small rounded or elliptical grains resembling fish roe;
when coarse they are called pisolites. Many of them are very pure and
highly fossiliferous. The oolitic grains in section may have a
nucleus, e.g. a fragment of a shell, quartz grain, &c., around which
concentric layers have been deposited. In many cases there is also a
radiating structure. They consist of calcite or aragonite, and between
the grains there is usually a cementing material of limestone mud or
granular calcite crystals. Deposits of silica, carbonate of iron or
small rhombohedra of dolomite are often found in the interior of the
spheroids, and oolites may be entirely silicified (Pennsylvania,
Cambrian rocks of Scotland). Oolitic ironstones are very abundant in
the Cleveland district of Yorkshire and form an important iron ore.
They are often impure, and their iron may be present as haematite or
as chalybite. Oolitic limestones are known from many geological
formations, e.g. the Cambrian and Silurian of Scotland and Wales,
Carboniferous limestone (Bristol), Jurassic, Tertiary and Recent
limestones. They are forming at the present day in some coral reefs
and in certain petrifying springs like those of Carlsbad. Their chief
development in England is in the Jurassic rocks where they occur in
large masses excellently adapted for building purposes, and yield the
well-known freestones of Portland and Bath. Some hold that they are
chemical precipitates and that the concentric oolitic structure is
produced by successive layers of calcareous deposit laid down on
fragments of shells, &c., in highly calcareous waters. An alternative
hypothesis is that minute cellular plants (_Girvanella_, &c.), have
extracted the carbonate of lime from the water, and have been the
principal agents in producing the successive calcareous crusts. Such
plants can live even in hot waters, and there seems much reason for
regarding them as of importance in this connexion.

Another group of limestones is of inorganic or chemical origin, having
been deposited from solution in water without the intervention of
living organisms. A good example of these is the "stalactite" which
forms pendent masses on the roofs of caves in limestone districts, the
calcareous waters exposed to evaporation in the air of the cave laying
down successive layers of stalactite in the places from which they
drip. At the same time and in the same way "stalagmite" gathers on the
floor below, and often accumulates in thick masses which contain bones
of animals and the weapons of primitive cave-dwelling man. Calc
sinters are porous limestones deposited by the evaporation of
calcareous springs; travertine is a well-known Italian rock of this
kind. At Carlsbad oolitic limestones are forming, but it seems
probable that minute algae assist in this process. Chemical deposits
of carbonate of lime may be produced by the evaporation of sea water
in some upraised coral lagoons and similar situations, but it is
unlikely that this takes place to any extent in the open sea, as sea
water contains very little carbonate of lime, apparently because
marine organisms so readily abstract it; still some writers believe
that a considerable part of the chalk is really a chemical
precipitate. Onyx marbles are banded limestones of chemical origin
with variegated colours such as white, yellow, green and red. They are
used for ornamental work and are obtained in Persia, France, the
United States, Mexico, &c.

Limestones are exceedingly susceptible to chemical changes of a
metasomatic kind. They are readily dissolved by carbonated waters and
acid solutions, and their place may then be occupied by deposits of a
different kind. The silification of oolites and coral rocks and their
replacement by iron ores above mentioned are examples of this process.
Many extensive hematite deposits are in this way formed in limestone
districts. Phosphatization sometimes takes place, amorphous phosphate
of lime being substituted for carbonate of lime, and these replacement
products often have great value as sources of natural fertilizers. On
ocean rocks in dry climates the droppings of birds (guano) which
contain much phosphate, percolating into the underlying limestones
change them into a hard white or yellow phosphate rock (e.g. Sombrero,
Christmas Island, &c.), sometimes known as rock-guano or mineral
guano. In the north of France beds of phosphate are found in the
chalk; they occur also in England on a smaller scale. All limestones,
especially those laid down in deep waters contain some lime phosphate,
derived from shells of certain brachiopods, fish bones, teeth, whale
bones, &c. and this may pass into solution and be redeposited in
certain horizons, a process resembling the formation of flints. On the
sea bottom at the present day phosphatic nodules are found which have
gathered round the dead bodies of fishes and other animals. As in
flint the organic structures of the original limestone may be well
preserved though the whole mass is phosphatized.

Where uprising heated waters carrying mineral solutions are proceeding
from deep seated masses of igneous rocks they often deposit a portion
of their contents in limestone beds. At Leadville, in Colorado, for
example, great quantities of rich silver lead ore, which have yielded
not a little gold, have been obtained from the limestones, while other
rocks, though apparently equally favourably situated, are barren. The
lead and fluorspar deposits of the north of England (Alston Moor,
Derbyshire) occur in limestone. In the Malay States the limestones
have been impregnated with tin oxide. Zinc ores are very frequently
associated with beds of limestone, as at Vieille Montagne in Belgium,
and copper ores are found in great quantity in Arizona in rocks of
this kind. Apart from ore deposits of economic value a great number of
different minerals, often well crystallized, have been observed in
limestones.

When limestones occur among metamorphic schists or in the vicinity of
intrusive plutonic masses (such as granite), they are usually
recrystallized and have lost their organic structures. They are then
known as crystalline limestones or marbles (q.v.). (J. S. F.)

LIMINA APOSTOLORUM, an ecclesiastical term used to denote Rome, and especially the church of St Peter and St Paul. A _Visitatio Liminum_ might be undertaken _ex voto_ or _ex lege_. The former, visits paid in accordance with a vow, were very frequent in the middle ages, and were under the special protection of the pope, who put the ban upon any who should molest pilgrims "who go to Rome for God's sake." The question of granting dispensations from such a vow gave rise to much canonical legislation, in which the papacy had finally to give in to the bishops. The visits demanded by law were of more importance. In 743 a Roman synod decreed that all bishops subject to the metropolitan see of Rome should meet personally every year in that city to give an account of the state of their dioceses. Gregory VII. included in the order all metropolitans of the Western Church, and Sixtus V. (by the bull _Romanus Pontifex_, Dec. 20, 1584) ordered the bishops of Italy, Dalmatia and Greece to visit Rome every three years; those of France, Germany, Spain and Portugal, Belgium, Hungary, Bohemia and the British Isles every four years; those from the rest of Europe every five years; and bishops from other continents every ten years. Benedict XIV. in 1740 extended the summons to all abbots, provosts and others who held territorial jurisdiction.

LIMITATION, STATUTES OF, the name given to acts of parliament by which rights of action are limited in the United Kingdom to a fixed period after the occurrence of the events giving rise to the cause of action. This is one of the devices by which lapse of time is employed to settle disputed claims. There are mainly two modes by which this may be effected. We may say that the active enjoyment of a right--or possession--for a determined period shall be a good title against all the world. That is the method known generally as Prescription (q.v.). It looks to the length of time during which the defendant in a disputed claim has been in possession or enjoyment of the matter in dispute. But the principle of the statutes of limitation is to look to the length of time during which the plaintiff has been out of possession. The point of time at which he might first have brought his action having been ascertained, the lapse of the limited period after that time bars him for ever from bringing his action. In both cases the policy of the law is expressed by the maxim _Interest reipublicae ut sit finis litium_.

The principle of limitation was first adopted in English law in connexion with real actions, i.e. actions for the recovery of real property. At first a fixed date was taken, and no action could be brought of which the cause had arisen before that date. By the Statute of Westminster the First (3 Edward I. c. 39), the beginning of the reign of Richard I. was fixed as the date of limitation for such actions. This is the well-known "period of legal memory" recognized by the judges in a different class of cases to which a rule of prescription was applied. Possession of rights in _alieno solo_ from time immemorial was held to be an indefeasible title, and the courts held time immemorial to begin with the first year of Richard I.

A period absolutely fixed became in time useless for the purposes of limitation, and the method of counting back a certain number of years from the date of the writs was adopted in the Statute 32 Henry VIII. c. 2, which fixed periods of thirty, fifty and sixty years for various classes of actions named therein. A large number of statutes since that time have established periods of limitation for different kinds of actions. Of those now in force the most important are the Limitation Act 1623 for personal actions in general, and the Real Property Limitation