Geology.— The central part of Ireland is occupied by a great undulating plain, whose highest elevation is 300 and average elevation about 200 feet. In the centre of the country, from Dublin Bay on the east to Galway Bay on the west, this plain stretches from shore to shore, but towards the south and north it is enclosed by an irregular semicircular belt of mountainous country. The surface of the plain is broken occasionally by isolated hills. Throughout nearly the whole of its extent it rests on the Carboniferous Limestone, and in several places there are remains of the Upper Carboniferous strata or Coal-measures, by which the Carboniferous Limestone was at one time overlaid, and which have been carried away during a vast period of denudation chiefly by the action of subaerial agents. The strata of limestone are nearly horizontal, except where they are contorted by local disturbances. In the central plain it is only occasionally that the limestone crops to the surface, as it is generally overlaid by boulder clay, the result of glacial action, by the middle sands and gravels formed on the bed of the shallow sea by which the plain was at one time occupied, or by the peat bogs resting on the beds of previous lakes. At one period the Carboniferous beds must have extended widely beyond their present limits, and have formed the surface strata of the uplands to the north-west and south-east. In the north-western highlands of Sligo, Leitrim, and Fermanagh they still form a lofty table-land, which occasionally rises into peaks about 2000 feet in height.

The mountain masses of Ireland are generally traversed by deep and narrow valleys running both north and south and east and west, and frequently giving rise to high and isolated peaks. The districts of Donegal and Derry in the north-west, and those of Galway and Mayo in the west, consist chiefly of metamorphosed Lower Silurian rocks, and are believed to form part of the same geological system as that of the Highlands of Scotland. Those of Donegal and Derry, lying between Donegal Bay and Lough Foyle, consist of granite, gneiss, and hornblendic and other schists, with crystalline limestones and quartzites. Their principal peaks are the isolated summit of Errigal (2466 feet) and Blue Stack (2219 feet). In West Galway and Mayo the rocks consist chiefly of quartzite, or of alternating beds of quartzite and granite or gneiss schist. They include the Twelve Pins of Connemara (2395 feet), Croagh Patrick on the shores of Clew Bay (2510 feet), the Nephin Beg mountains, and the Ox mountains. The range of hills between Killary Harbour and Lough Mask—the highest summit of which, Muilrea, has an elevation of 2688 feet—belongs to the Upper Silurian formation. The fact that these rocks do not share in the metamorphism of the Lower Silurian beds shows that the alteration must have taken place at some time between the Lower Silurian and Upper Silurian periods. Rocksof Cambrian age occur in Wexford, Wicklow, and Dublin. The principal elevations of these districts are formed of granite, and belong to an earlier epoch than that of the Old Red Sandstone. The highest summit is Lugnaquilla (3039 feet), composed of altered Silurian rocks lying on the granite. In the south-western districts of Kerry, Cork, and Waterford, the mountains are composed of broad bands of Old Red Sandstone, the valleys being formed of narrow bands of Carboniferous rocks. The lie of the strata is nearly east and west, since they have been plicated by forces acting in a transverse direction, the time of disturbance being some unknown date between the Carboniferous and the Permian periods. This district includes the rugged range of Macgillicuddy’s Reeks, which rise abruptly from the Carboniferous Limestone surrounding the Killarney lakes, and, occupying the greater part of the peninsula between Dingle Bay and Kenmare River, attain at Carntual a height of 3414 feet above sea-level. Many of the most conspicuous mountain groups in the southern half of the island consist of central cores of Silurian strata wrapped round with thick folds of Old Red Sandstone. Such are Slieve Aughty, Slieve Bernagh, the Silver Mine mountains, and Slievenaman in Clare and Tipperary, Galtymore in Limerick, which has an elevation of 3015 feet, and the Slieve Bloom mountains in Queen’s county. The principal mountain groups in the north-east are the Carlingford mountains, composed of felspathic and pyroxenic rocks, and attaining in Slieve Foy a height of nearly 2000 feet; the Mourne mountains to the north of Carlingford Lough, composed of granite, with veins of basalt, felstone, mica trap, and porphyry, the highest summit being Slieve Donard (2796 feet); and the Slieve Croob mountains, to the north of the Mourne range, composed of granite of a much earlier origin. Both the Mourne and Carlingford mountains are of intrusive origin, and probably belong to the Permian period. A considerable extent of low country in Down, Armagh, and Cavan is occupied by Silurian rocks in the form of grits and slates. The estuary of Belfast Lough lies in Triassic rocks, containing beds of rock salt. Rocks of similar age extend west of Lough Neagh, and thence, north to Lough Foyle. They are overlaid by Jurassic and Cretaceous strata, which, however, are almost wholly concealed under the great basalt flood of the northeastern counties. The greater part of Antrim and the eastern portion of Derry are occupied by basalt rock forming an elevated plateau, for the most part bounded towards the sea by precipitous escarpments, consisting of Upper Greensand and Chalk, surmounted by the black basalt which, often crowning their summits, stands in striking contrast Table I.— Area and Distribution of Land in 1880, and Population in 1881. [table]

with the light-coloured strata below. In some places, however, as at the Giant’s Causeway, the Cretaceous rocks disappear, and the basalt slopes gradually to the sea, displaying a series of terraces formed of hexagonal pillars, and occasionally separated by bands of volcanic ash.

Coast-Line.— Along the present coast-line there are to be seen in several places traces of ancient sea margins, the most continuous being those on the northern and eastern coasts, especially in county Antrim. Of still more ancient sea margins there are evidences in the terraces at the base or on the flanks of the mountains. The present coast-line, especially on the west and south, is very much indented by bays and inlets, which Hull, in his Geology of Ireland, attributes in many cases to the chemical action of the sea-water on the limestone rocks. On the south coast they most commonly run in a northerly direction with a westerly inclination at the upper end, and on the west coast the direction of the larger inlets is easterly, although several of the smaller ones run north, south, and north-east. Their troughs have mostly been excavated in the synclinal folds of the rocks, which therefore frequently project far into the sea in the form of high and bold headlands. On the northern coast the inlets generally run in a southerly or south-westerly direction. Most of those on the east coast have by the accumulation of sand been either wholly or partly formed into lagoons; and on the south east coast the sea has made considerable encroachments on the land.

The principal inlets are—on the east coast Belfast Lough, Strangford Lough, Carlingford Lough, Dundalk Bay, Dublin Bay, and Wexford Harbour; on the south coast Waterford Harbour, Dungarvan Harbour, Youghal Bay, and Cork Harbour; on the south-west coast Roaring Water Bay, Dunmanus Bay, Bantry Bay, Kenmare River, and Dingle Bay; on the west coast Tralee Bay, the mouth of the Shannon, Galway Bay, Clew Bay, Blacksod Bay, Killala Bay, Sligo Bay, and Donegal Bay; and on the north coast Sheep Haven, Lough Swilly, and Lough Foyle. In all, Ireland possesses fourteen harbours suitable for the largest ships, seventeen for frigates, and over thirty for coasters, besides an immense number suitable for fishing boats.

The islands of Ireland are small in size, and are situated near the mainland, most of them being formed of rocks from which, according to Hull, the adjoining Carboniferous strata had been denuded by the action of the sea-water. They are most numerous on the west coast, especially opposite Galway, Mayo, and Donegal. Off the Donegal coast the largest is Neish Aran. Separated from the mainland of Mayo by a narrow isthmus is Achill, the largest island of Ireland, and in Clew Bay there are an immense number of islets all formed of drift. An archipelago of granite rocks off the coast of Galway is formed of continuations of the mountains, and at the mouth of Galway Bay are the three islands of Aran, composed of Carboniferous Limestone. Among the picturesque stacks of rocks off the coast of Kerry the most notable are the Skellings. The largest islands opposite Cork are Dursey Island, Bear Island, and Clear Island, south of which is a picturesque rock called the Fastnet, on which there is a lighthouse. On the east coast the principal are Lambay Island, Innis-patrick, and Ireland’s Eye off county Dublin, and Copeland Island at the mouth of Belfast Lough. On the northern coast the principal are Rathlin Island off Antrim, and Tory Island off Donegal.

Divers and Canals.— Several of the rivers of Ireland, including the largest of them, have had their channels determined by a previous physical condition of the land surface, and must have been formed during a long period of denudation. Many of the valleys are dried-up river beds, and along various of the present river valleys traces of old river terraces may still be seen. In some cases the alterations of the courses by breaks and dislocations of the strata are of very recent occurrence. In the districts of Sligo and Fermanagh, as well as of Galway, Clare, Kerry, and Cork, the rivers and streams have frequently cut out subterraneous passages through the limestone, in some cases altogether disappearing; and along their courses turloughs or blind lakes, and abrupt deep holes called sluggas are frequently formed.

Owing to the moistness of the climate and the lie of the surface of the country, Ireland is more intersected by large rivers than England or Scotland, and it is a remarkable circumstance that in several cases there are groups of rivers with closely contiguous sources, which, however, flow in widely different directions. The largest river is the Shannon, which has its source in the Carboniferous mountains of Fermanagh and Leitrim, and flows southward through Lough Allen, Lough Ree, and Lough Dearg to Limerick, where it opens out into a wide estuary and takes a westerly course to the ocean. Up to Limerick, where it becomes tidal, it is navigable for large vessels, and for vessels of small tonnage it is navigable within 5 miles of Lough Allen. Its course above Lough Dearg is very sluggish, but from that lake to Limerick its descent is very rapid. Its total length is 240 miles, and it drains an area of 4544 square miles. The Suir, the Nore, and the Barrow, which have their sources not far from each other in the Slieve Bloom mountains, and unite at Waterford, drain together an area of 3400 square miles. The Suir is navigable for boats as far as to Clonmel, and the Nore to Innistioge. The Barrow, by means of a branch of the Grand Canal, forms a line of 120 miles of inland navigation between Dublin and Waterford. The other principal rivers, all of which are to some extent navigable, are—debouching on the west coast the Erne, the Moy, and the Corrib; on the south coast the Blackwater and the Lee; on the east coast the Lagan, the Boyne, the Liffey, and the Slaney; and on the north coast the Bann and the Foyle.

The Grand Canal, which with its various branches has a length of 165 miles, connects Dublin with the Shannon at Shannon Harbour; and the Royal Canal, with a length of 76 miles, connects Dublin with the Shannon at Cloondora. Lines of inland navigation, partly natural and partly artificial, connect Lough Neagh with Belfast, Newry, and Lough Erne. From the sea at Galway there is communication by Lough Mask and Lough Corrib to Lough Carra. Since the introduction of railways the passenger traffic on the canals has wholly ceased, but the goods traffic is still considerable.

Lakes.— Many lakes of considerable extent exist both in the mountainous and lowland districts of Ireland, and the number of small lakes is very great. Altogether the area covered by lakes amounts to 711 square miles, of which 287 are in Ulster, 305 in Connaught, 69 in Munster, and 50 in Leinster. Lough Neagh in Ulster is the largest inland lake in the United Kingdom, and has an area of 153 square miles, with a general depth of from 20 to 40 feet. Lough Erne in Fermanagh has a length of upwards of 40 miles, but a breadth of only 8 miles. Properly speaking, it consists of two lakes 5 miles apart and connected by a river, the upper lake being 13 miles in length with an area of 9278 acres, and the lower 24 miles in length with an area of 28,000 acres. Both lakes are dotted with numerous islets, and the lower one is famed for its picturesque beauty. Lough Corrib and Lough Mask have respectively an area of 43,484 and 22,219 acres. The country to the west of Lough Corrib contains about 130 lakes, 25 of which are more than a mile in length. The lakes of Killamey in Kerry, which are three in number and closely adjoin each other, are situated in the midst of wild and picturesque mountain scenery. The area of the lower lake is 5001 acres, of the middle one 680, and of the upper one 430, Lough Dearg, a small lake in the south of Donegal, has been resorted to from time immemorial as a place of penance by Roman Catholics. The other lake of the same name in the course of the Shannon has an area of 29,570 acres. The other principal lake districts are Sligo, Cavan, Westmeath, and Longford. Hull, in his Geology of Ireland, makes a classification of the lakes, according to their modes of formation, under the three heads of—(1) lakes of mechanical origin, (2) lakes of glacial origin, and (3) lakes of chemical solution. Of the first group, which are those whose formation is due chiefly to faults or dislocation of the strata, he mentions as special examples Lough Neagh and Lough Allen, both of which originated before the Glacial period, and probably between the Miocene and Pliocene periods. Those of glacial origin occur in the mountainous districts, and are due either to the scooping out of the rocks by the passage of ice over their surface, or to the accumulation of embankments at the end of the valleys or hollows. Those due to chemical solution are situated either on the limestone plain or in districts where the limestone formation has penetrated, and have been produced by the solution of the limestone through the action of water containing carbonic acid gas. , Coal.— Of the Upper Carboniferous beds which at one time overspread the central plain of Ireland, only small patches remain in isolated spots, serving chiefly as an indication of the immense loss that has been sustained in an important element of material prosperity. The principal coal-fields are the Leinster, the Munster, the Connaught, and the Tyrone.

The Leinster or Castlecomer field, situated between the Nore and Barrow, consists of a range of hills varying from 800 to 1000 feet high, and extending over portions of Kilkenny, Queen’s county, and Carlow. It lies in the form of a basin, its most productive beds occupying the centre. These are the Middle Measures, but in the field both the Middle and Lower are represented. The coal is anthracite. The most common fossils are either terrestrial or freshwater, marine fossils being found chiefly in some of the upper beds. Above the Barrow coal in county Kilkenny several remarkable reptilian remains have been found. The Lower Measures consist of gannister beds resting upon Carlow flags, and contain some beds of shale and a few thin seams of coal, with several beds of marine fossils. This field is the most important in Ireland, and yields a larger weight of coal than all the others together.

The West Munster coal-field occupies portions of Clare, Limerick, Kerry, and Cork, and consists of a series of low hills extending from near Galway Bay in the north to Killarney in the south. All the three measures are represented, but there are only a very few workable seams, as most of the coal is very thin, and the strata very much inverted. The principal collieries are at Dunhallow in Cork, and the coal, which is anthracite, is used chiefly for lime-burning. Many of the Lower Measures are very rich both in terrestrial and in marine fossils.

The East Munster coal-field consists of a low range of hills in Tipperary, closely adjoining the Carboniferous hills in Leinster, from which they are separated by the river Nore. Thence it extends to near Cashel, a distance of about 20 miles, and its average breadth is about 5 miles. All the measures are represented. The productive portion of the field is at Killenaule, and consists of two thin seams in the Upper Measure. In the Lower Measures the principal fossils are marine; and plant impressions, especially those of ferns, are very numerous.

The Connaught coal-field embraces the mountainous district round Lough Allen, and includes portions of Sligo, Roscommon, and Leitrim in Connaught, and of Fermanagh and Cavan in Ulster. Both the Middle and Lower Measures are represented. They are composed chiefly of yellow sandstone and shale, and are overlaid by beds of grit. The coal is bituminous, and a large portion of it is workable.

The Tyrone coal-field includes the district between Dungannon and Lough Neagh, having a length of 6 and a breadth of 1 to 2 miles, and the small basin of Annaghone a little to the north. All the measures are represented. The coals have been worked only near the surface, but it is believed that very extensive and valuable seams of workable coal exist at lower depths.

The average quantity of coal raised in Ireland annually is about 130,000 tons, of which about 80,000 are raised in Leinster, 30,000 in Munster, 16,000 in Antrim and Tyrone, and 6000 in Leitrim and Roscommon. As the annual importation of coal exceeds 2,000,000 tons, it is evident that the coal supply obtained from Ireland’s own mines is quite a minor element in its prosperity; but the industry might be much more largely developed, the total available amount of coal being estimated at 180,000,000 tons.

Peat.— For the absence of coal the country is to some extent compensated by the supply of peat fuel obtained from the red bogs situated in the central plain, and occupying a large tract included within two lines drawn across the island, the one from the Hill of Howth to Sligo, and the other from Wicklow to Galway. Originally this district was occupied by a forest, principally of oak trees, which after being gradually killed by the growth of mosses and other peat-producing plants, were succeeded by a forest of firs, these also in turn perishing. The average depth of the bog is 25 feet, but in some cases it is over 40 feet. According to its...

Irenaeus holds the same relation to the theology of the Greek fathers that Tertullian does to the doctrinal system of the Church of the West. In tracing back the history of a doctrine, it is common to find it first taking shape in the writings of one or both of these early theologians. Hence the great value of his writings. It is from Irenaeus also that we get the earliest form of the creed which afterwards, through the labour of councils and theologians, became what we now know as the Niceno-Constantinopolitan creed (Lumby’s History of the Creeds, p. 14, cf. Schaff, The Creeds of the Latin and Greek Churches, p. 40). The only writing of Irenaeus which has come down to us, with the exception of fragments, is his work Against Heresies, and for this reason his opinions are all expressed by way of controversy. The treatise is divided into five books: of these the first two contain a minute description and criticism of the tenets of various heretical sects, both Gnostic and Ebionite; the other three set forth the true doctrines of Christianity, and it is from them that we find out the theological opinions of the author. Irenaeus as a Christian theologian lays great stress on the existence of the Christian church, and on the necessity of life within the church. Christianity does not consist merely in the possession of knowledge, but in partaking in a life which is to be lived in the world and beyond it. Believers have a common religious experience, and this rests both upon facts outside · them and upon their association together within the church, while it implies a community of knowledge. The church rests upon the common facts contained, in the gospel history; her historical succession of pastors places her in direct and outward relation to Christ, to whom her pastors ought to be inwardly related also by spiritual consanguinity. Her common knowledge—the true Gnosis, and not the false of the Gnostic—comes from the Holy Scriptures, which in Old Testament and New are inspired by the Holy Spirit and contain the truth of God. The church has also got, coming to her from apostolic times, and giving authoritatively the interpretation of the Scripture, certain forms of sound words or rules of faith which keep her from heresy. In speaking of God Irenaeus is careful to insist that the God of the Christian church is the maker of heaven and earth, and the God of Abraham, Isaac, and Jacob; for it was a Gnostic inference from the supposed sinfulness of matter that the good God could not defile Himself with matter in a work of creation, and some carried their antipathy to the Old Testament so far as to make the Hebrew Jehovah a malignant deity whom Christ had come to destroy. Irenaeus is at pains to explain that Christ, the Logos of God, the Saviour, is true man and true God, in opposition to the Gnostic Docetae who taught that our Lord’s body was only an assumed phantasm, and in contradiction to the Ebionites, who acknowledged Christ to be the last of the prophets, and looked upon Christianity as Judaism with a new prophet, but refused to confess him true God of true God. Irenaeus also lays great stress upon the doctrine of the Trinity. His exposition is by no means either so full or so precise as that of theologians who write after the council of Nicaea, but he insists on the equality in divinity of the three persons, Father, Son, and Holy Ghost. The plan or method of salvation is commonly represented under the idea of a covenant, which word is used more in the sense of promise than of bargain. Sometimes the covenant is represented as twofold,—that given to the favoured nation and symbolized in the Mosaic economy, and that given to those who are not the descendants of Abraham and promised in the gospel; sometimes it is fourfold, and Irenaeus speaks of a covenant given to Noah, and renewed through Abraham and Moses, and lastly in the gospel of our Lord. It is difficult to state with any precision what Irenaeus holds about the nature of the effect of Christ’s work of reconciliation upon man. He makes great use of metaphor, and evidently had not learnt to express himself otherwise. The doctrine was still in its pictorial state in his mind. Still, traces appear of that tendency afterwards common in the Greek Church to make the incarnation rather than the crucifixion and ascension of our Lord the most important part of his work, and to look upon the effect of that work as a transfusion of the incarnation through redeemed humanity. The doctrine of the sacraments is also too metaphorically expressed to admit of precise statement; but Irenaeus seems to believe that in the sacrament of the Lord’s Supper it is the heavenly body of Christ which is actually partaken of in the elements, and that such participation gives immortality.

Our knowledge of the writings of Irenaeus comes principally from Eusebius. That church historian tells us that Irenaeus wrote a Letter to Florinus, and a tract On the Valentinian Octave (of Aeons), both against Gnostic theories; a Letter to Pope Victor, and another to Blastus, also at Rome, both on the Easter controversy; a work, probably on apologetic, called ∏pδs "Eλληvαs λJγos . . . ιreρl eπι- 7τημηs iπιγeypaμμevos ', a Picture of .Apostolic Preaching·, and a book of aphorisms. According to Photius, Irenaeus wrote also on the Substance of the World. Fragments from these lost works and perhaps from others have been recovered from Eusebius, from Maximus of Turin, from Leontius of Byzantium, from John of Damascus, and from several collections of fragments, some of which were discovered in European libraries, and others came to the British Museum among Syriac MSS. from the Nitrian convents. The only work of Irenaeus which has come to us entire is the treatise Against Heresies. The original Greek text, except the greater part of the first book, which has been preserved in quotations in Hippolytus and Epiphanius, has been lost, and the treatise has been preserved in a somewhat barbarous Latin version. The first edition was published by Erasmus in 1526. He used three MSS. which have since been lost. In 1570 Gallasius, a Calvinist professor in Geneva, published a new edition. He had before him the Greek text as far as given in the quotations in Epiphanius. The next important edition was that of Feuardent in 1596, and frequently reprinted. Feuardent used a Vatican MS. In 1702 Grabe published at Oxford a new edition, greatly better than preceding ones. He used the Aπιndel codex. In 1710 the Benedictine Massuet published at Paris another edition, in which three new MSS. were used. It long continued the standard, and forms the 5th volume of the Abbé Migne’s Pairologia Graeca, Paris, 1857. A valuable edition was published in 1849-53 by Adolph Stieren, which really superseded the others. The fragments discovered among the Syriac MSS., however, are only to be found in the Cambridge edition of 1857, edited by the Rev. Wigan Harvey. The extant writings of Irenaeus, including the fragments, have been translatedand published in Clark’s Ante-Nicene Library. The facts of Irenaeus’s life and his dogmatic teaching and ecclesiastical position may be learnt from the prefaces of Feuardent, Massuet, and Stieren, as well as from such church historians as Tillemont, Schrock, Neander, and Fr. Chr. Baur. There is a very valuable monograph upon Irenaeus in Erseh and Gruber’s Encyclopädie, II. section, vol. xxiii., written by Stieren, the editor of the German edition. This was written, however, before the Syriac versions were discovered. (T. Μ. L.)

See V. Mignot’s Histoire de l'Imperatrice Irène, 1762; Gibbon’s Beeline and Fall ; Milman’s Latin Christianity ; Le Beau’s Bas-Empire ; and Schlosser’s Geschichte der bilderstürmenden Kaiser des oströmischen Reichs, 1812.

1RIARTE, or Yriarte, Tomas de (1750-1791), Spanish poet of the age of Charles III., was born September 18, 1750, at Orotava in the island of Teneriffe, and received his literary education at Madrid under the care of his uncle, Juan de Iriarte, a scholar who for forty years was head of the royal library, and whose name as a collector of proverbs still finds a place in the literary annals of his country. In his eighteenth year the nephew began his literary career by translating French plays for the royal theatre, and in 1770, under the anagram of Tirso Imarete, he published an original comedy entitled Hacer que kacemos. In the following year he received an appointment as official translator in the foreign office, and in 1776 he became a ’keeper of the records in the war department. For a short time he now edited a journal entitled the Mercurio Politico, and during this period of his life he added to the number of his original dramas (the best of these being La Sehoriia mal criada), and also composed various minor poems. In 1780 appeared his didactic poem La Musica, the outcome of his proficiency in music, which attracted some attention in Italy and France as well as at home. It is composed in those masses of irregular lines known nationally as silυas, and consists'of five books which severally treat of the elements of music, the various kinds of musical expression, the music of the theatre, of society, and of solitude. Its poetical merit is very small. In 1782 appeared the Fdbulαs Literarias, with which his name is most intimately associated. The work is of interest to the student of Spanish literature as being the first original attempt at fable-writing in that language; the stories, which numbered in the first edition about sixty and afterwards increased to eighty, are composed in a great variety of metres, and show in many cases considerable ingenuity (sometimes, it must be confessed, very far-fetched) and careful execution. As their name is intended to imply, they all relate to the follies and weaknesses of literary men. They have been translated into several European languages. An English version by Rockliffe reached a third edition in 1866. During his later years, partly rn consequence of the Fabulas, he became involved in troubles with several of his literary contemporaries; and in 1786 he was charged before the Inquisition with having manifested leanings towards the new French philosophy. He died September 17, 1791.

The first collected edition of his works (Oδrαs), prepared by himself, appeared at Madrid in six volumes in 1787; another, more complete, in eight volumes, in 1805. They include, besides those already mentioned, translations of the Λrs Pocticα of Horace and of the first four books of the Aencid, and also some metrical epistles.