again throwing up huge and abrupt mountain masses, and so causing that inequality of surface which is alike beautiful and useful in the external economy of man's earthly abode. The same agency operates, and has for ages operated, on a smaller scale, in volcanoes, earthquakes, and a gradually elevating force, such as is at present observable on the shores of Siberia, in the islands of the Arctic Seas, in several parts of the coasts of the South American Continent, and in the island groups of the Southern Ocean.1 Then again, we have on every side the marks of a comparatively more recent, but scarcely less powerful agency, in the form of an universal deluge, rolling along vast masses of débris, scooping out immense tracts, and leaving, in the abraded sides and corresponding strata of the surrounding mountains, indelibly and plainly written, the history of the origin of these 'valleys of denudation.' The natural result of these phenomena, is that we generally find the strata, or layers of rocks forming the earth's crust, dipping, or inclining at various angles; we sometimes find them all but vertical, sometimes nearly curvilinear, sometimes bent and contorted, in fact, most variously disposed; and thus it is that several of the earlier rocks are brought to the surface. The strata are also frequently varied by what are technically called slips, faults, hitches, and dykes, the results of igneous agency, or are infiltered by metallic lodes and veins. Nowhere do we meet with a greater variety of stratification, resulting from both igneous and aqueous agencies, than in the British isles, where, happily, are to be found on all sides that natural mixture of soils, and those facilities for their artificial improvement which are of so much advantage to agriculture. 1 In addition to these there are other minor changes, slowly but constantly going on. In some places there is a gradual subsidence, and in others a submersion of considerable tracts by encroachments of the sea. Of this latter, we have instances in the harbour of Youghal, where, at low water, may be seen extensive remains of submerged bogs, at a considerable distance from high water mark. THE FORMATION OF SOILS. 69 CHAPTER XVII. THE SOIL, HOW FORMED; PARTAKES LARGELY OF THE CHARACTER OF THE SUBJACENT ROCK; HOW THE NATURAL MIXTURE OF SOILS IS EFFECTED; EXTRAORDINARY FERTILITY OF THE GOLDEN VALE-DEPOSITS OF SAND AND GRAVEL; ALLUVIAL DEPOSITS; DELTAS-TWO-FOLD ADVANTAGE OF A MIXTURE OF SOILS, MECHANICAL AND CHEMICAL-CONSTITUENTS OF PLANTS, IN VARYING PROPORTIONS, IN THE SOILS OF ALL ROCKS→→→ ARTIFICIAL MIXTURE OF SOILS BY THE SKILFUL AGRICULTURIST, AS EXEMPLIFIED IN NORFOLK AND BELGIUM. THE soil, generally speaking, is the result of the gradual disintegration or pulverising of the surface of the rock, mixed with the residuum of the vegetable matter constantly forming upon it. The soil, therefore, largely partakes of the character of the rock from which it has had its origin. It is sandy, if the rock is sandstone; more or less of a tenacious clay, if the rock is claystone; more or less calcareous,' if a limestone; and, if the rocks are mixed, as at the intersection or juxtaposition of two or more strata on the surface, then the soil is of a mixed character, and generally remarkable for its fertility. Thus, as frequently occurs, the rock of a lower formation, penetrating the superincumbent strata, causes a mixture of their soils with each other, or with its own, at the point of intersection; and the result is a fine rich loam, such as that described by Young and Wakefield, as found at the roots of mountains in Ireland.' The mixture of soils is also effected by the detritus which is being continuously carried down to the plains, by floods and rains, from the mountains, or their débris, which, at some remote period, was deposited there by the action of great bodies of water. In Ireland we have abundant evidence of the country having, at a far distant epoch, been long subjected to the action of water. Thus, we find the débris of the surrounding mountains in several parts of the great central plain, and of the smaller 1 Calcareous (Latin, calx, lime), partaking of the nature of lime. valleys, generally mixed with their calcareous soil; but, in some instances, so completely overlaying it as not to exhibit a trace of lime. To the mixture of soils resulting from the above causes may be attributed much of the extraordinary fertility of the Golden Vale, running through the counties of Limerick and Tipperary, and of other rich tracts (such as have already been described in the extracts I have quoted) in different parts of the country. We frequently find regular layers of gravel and sand between the vegetable mould and the rock, these layers being evidently the result of the long-continued action of water. Again, in some places, as in parts of Norfolk, and on the coasts of Belgium, the surface is composed of barren sands washed in from the sea; and, in others, it consists of rich alluvial deposits at the mouths or on the banks of rivers, such as the deltas of the Nile,' the Mississippi, and the Ganges, or the caucasses of the Fergus and Shannon. In all such cases the soil differs very much, if not altogether, from the character of the rock on which it rests. The advantages resulting from a mixture of soils are twofold-mechanical and chemical. First, a clay soil, in itself too retentive of moisture, will be improved by a mixture of chalk or sand; whilst, on the other hand, chalky or sandy soils, which part their moisture too readily, will derive much benefit from a mixture of clay. Next, it has been ascertained by chemical analysis, that in the ash of all plants, wild or cultivated, there are twelve or fourteen different mineral substances, in greater or less relative proportions; and, therefore, in a fertile soil, besides its organic matter, all these substances must necessarily exist in sufficient quantity for the requirements of the plants grown therein.2 Now, whilst in the soils of all rocks, stratified and unstratified, traces are found of all these mineral substances, or constituents of plants,3 they do not exist in the soil of any one particular rock in the requisite quantity to enable the plant to 1 Deltas. See Appendix XII. 2 Johnston's 'Agricultural Chemistry,' p. 134. 3 Ibid. p. 135. GOOD RESULTS OF THE MIXTURE OF SOILS. 71 acquire a sufficiency of each in the period of its growth. While some of these substances will predominate in a calcareous soil, they will be deficient in a sand or clay; while others again will be all but absent in the former, they will exist abundantly in the latter; and so on with other soils. Therefore, it is obvious that the simple soil of one particular rock will not possess in itself, in the requisite quantity, all those elements, essential to the growth of plants, which are furnished by a mixture of two or more soils. While much has been effected by natural causes in this respect, much has been left to be accomplished by human industry and science. A skilful agriculturist will artificially secure to himself the beneficial results of the mixture of soils, by making use of the materials which lie close at hand available for his purpose. Thus, we see the barren sands of Norfolk and Belgium transformed by the hand of man into tracts of the most blooming fertility, and supporting a prosperous agricultural population— strikingly in contrast with the naturally fertile soil of Ireland, which does not bear one half the produce that it might, with a population only partially employed, deficient in agricultural knowledge and enterprise, and consequently poor and discontented. CHAPTER XVIII. THE GREAT CENTRAL LIMESTONE PLAIN OF IRELAND; ITS AREA AND ELEVATION-THE BOGS OF IRELAND; THEIR AREA AND SITE; BOG of allen -ESKERS-THE DRIFT OR BOULDER FORMATION-THREE VARIETIES OF IN LIMESTONE THE interior of Ireland is a vast limestone plain, to a great extent surrounded by mountains of a primary or transition character towards the coast, with outliers in some of the central counties. This limestone formation extends 120 miles, east and west, from Dublin to Galway Bay, and about 100 miles, north and south, from Fermanagh to the counties of Cork and Waterford. With some gentle undulations, it is almost entirely flat; its average elevation above the level of the sea not exceeding 300 feet. Of this great plain of 12,000 square miles, or 7,680,000 statute acres, about one-fifth, comprising 2,460 square miles, or 1,576,000 acres, are flat bogs, holding a great quantity of stagnant water. The remaining four-fifths are for the most part fertile arable land. A line drawn from the hill of Howth to Sligo, on the north, and another line drawn from Wicklow-head to Galway, on the south, would comprise the district of the flat bogs of Ireland, which are partly in the counties of Roscommon, Galway, Westmeath, King's and Queen's Counties, and Kildare. Although separated in several places by ridges of the limestone soil, they bear the common designation of the Bog of Allen. Several mounds, hillocks, and ridges of sand and limestone gravel, called eskers,' occur in different parts of the plain, as in Meath, Westmeath, and the King's and Queen's Counties. The sand and gravel in some places lie in distinct and welldefined layers, and the mounds occasionally have the appearance of having been deposited by contending currents of water. These deposits of sand and gravel, and the boulder stones, generally water-worn and rounded, varying from a few ounces to several tons weight, and standing detached or in groups, but more frequently enclosed in boulder clay, constitute what is called the drift,' 'erratic block group,' or 'boulder formation.' There are three varieties in the limestone rock of Ireland— viz., the lowest, which is by far the most extensive, and prevails in the midland and southern counties-the middle limestone, or black shale series, called calp, found in the neighbourhood of Dublin, in Westmeath, Longford, and parts of Galway 1 Eskers, the same as the kaimes of Scotland and ösars of Sweden. |