CHAPTER III.

THE RELIEFS OF THE LAND SURFACE.

"Whatsoever the Lord pleased, that did he in heaven, and in the earth, in the seas, and in all deep places." · Ps. cxxxv. 6.

36. THE FORMS OF RELIEF on the globe are varied to an almost infinite extent; yet they may be classified, according to their most prominent features, into mountains, or highlands; plateaus, or table lands; and plains, or lowlands.

37. MOUNTAINS are vast elevations of land, either connected in lines or ranges distributed over the surface, and on the borders of plains and plateaus, or scattered in isolated groups, or forming the centre or knot of several chains.

38. In a system of mountains the central ridge has usually the boldest development and the highest elevation. The highest part of a range is called the crest.

39. From its common occurrence it seems to be a general

36. Forms of relief. 37. Mountains.-38. The crest. 39. General law

Projecting
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law for chains of mountains to have very steep declivities on one side, and very gradual slopes on the other. The An'dēs present a steeper face towards the Pacific Ocean than towards the main land of America; and generally the steepest declivity is towards the nearest sea.

40. Chains of mountains, though making many curves and angles, generally follow the direction of the greatest length of the continent or district in which they are situated.

41. Mountains which reach the height of 10,000 feet and upwards are of the first class; those ranging between 4000 and 10,000 feet are of the second class; those varying from 2000 to 4000 feet are of the third class; and the inferior elevations are styled hills and slopes.

42. Parallel chains having the same general direction, though separated by valleys, straits, or seas, resemble each other in geological formation; as the Atlas and Spanish mountains.

43. TERRACES are successive steps of descent from highlands to lowlands. A WATERSHED is the sloping of the land in several directions, determining the course of the flowing waters. The space enclosed by a watershed is called a BASIN, the lowest part of which is generally occupied by a lake, or traversed by a river.

for mountain chains. Relation of the slopes to the ocean.

40. Direction of mountain chains. -41. Height of first class mountains; second class; third class. Inferior elevations. 42. Resemblance of parallel chains. 43. Ter

Columnar

Terraced

Moraine

44. Mountain forms differ in appearance, and are described as being dome-shaped, volcanic, peaked, ser'rated, (jagged like a saw; hence the Spanish name sierra,) or colum'nar. This difference is owing to their geological structure.

45. PLATEAUS. An extensive mass of elevated land, with comparatively level surfaces, is called a plateau, or table land. It may have various undulations of hill and vale, be traversed by mountain ridges, and serve as a platform for lofty peaks; but its prevailing character is that of a highlyraised region on which there is a considerable area of plain surface; the whole presenting either gradual slopes, or abrupt. acclivities, and sometimes terrace-shaped sides, to the adjoining lowlands.

46. PLAINS are distinguished from table lands by being very little elevated above

the sea, in some instances even descending below it. The term is applied to an extent of country generally level as compared with mountainous districts, though the surface may be undulated, studded with low hills, traversed by valleys, or intersected by deep ravines. Plains constitute by far the greater portion of the earth's surface, and are the sites of its highest culture, greatest cities, and most numerous population.

47. Plains, though possessing certain features in cominon, present some peculiarities, as follows:

48. Landes, or Heaths. These occupy a large portion of the north of Germany and the south-west of France. They are sandy tracts, sometimes wholly bare, or clothed with heath

and pines, interspersed with fens and marshes.

races. Watershed. Basin. - 44. Varieties of mountain forms. -45. Pla teaus; their prevailing character. - 46. Of plains; extent. -47, 48. Peculi

49. Steppes. The Russian term steppe is applied to the extensive plains which occupy South-eastern Europe and North-western Asia. These have no uniform character, except that of being great lowland levels.

50. Deserts are tracts of bare sand, gravel, rocky slabs, and flinty stones, condemned to perpetual barrenness. Depressions of varying extent occur in the midst of the deserts, called Ō'ases, where there are springs and wells, nourishing groves of date trees and grasses.

51. Llä'nos. The plains of Venezuela and New Grenä'da, in South America, are so called. In the wet season they are inundated for hundreds of square miles; afterwards, when the waters have subsided, they are covered with a beautifully green verdure; and in the dry season the grass crumbles into dust, the whole appearing like a desert.

52. Sěl'vas. The plains of the Amazon, in South America, are covered with woods, interspersed with clear, grassy spaces and marsh lands. They comprise upwards of two million square miles, nearly one million of which is woodland.

53. Păm'pas. These form the third great division of South American lowlands, extending about eighteen hundred miles south from the selvas, and from the Atlantic to the Andes. They are treeless plains, covered with tall grass, thistles, &c., presenting also vast swamps and lagôôns'.

54. Savăn'nas, or Prairies. These are apparently boundless meadows, occupying vast tracts on both sides of the Mississippi, but principally on the west. They are described as undulating, or rolling, in the general aspect of their surfaces.

55. VALLEYS are of three kinds principal, lateral, or transverse, and subordinate. Principal valleys are usually of large dimensions, enclosed between extensive parallel ranges of mountains. To this class belongs the Valais, or Valley of the Rhone. Lateral valleys are so called because they are situated among transverse branches of mountain ranges. Subordinate valleys are of smaller size, formed by the spurs of mountain ranges, or situated among hills.

Some valleys are basin-shaped, being surrounded by a girdle of mountains, with the exception of one small outlet, which allows the escape of the surplus waters. The beautiful valley of Cashmere' presents an example of a basin

arities. Landes. 49. Steppes. 50. Deserts. Oases. 51. Llanos. 52. Selvas. 53. Pampas.-54. Savannas, or prairies. 55. Three kinds of valleys. Principal; example; lateral; subordinate. Basin-shaped; valleys ex

shaped valley. When valleys are narrow and difficult of access, they are termed ravines, glens, dells, defiles, gorges, gullies, passes, or ports. These are frequent among steep mountains, and often present scenes of great beauty and grandeur. They usually form the routes by which mountain chains are crossed, and often form the beds of rivers. The "Notch” in the White Mountains of New Hampshire affords an instance.

56. In high northern and southern latitudes, and at certain elevations in all latitudes, snow and ice occur on the surface of the globe as a permanent covering.

57. The snows accumulated on the tops and steep declivities of mountains are frequently precipitated, by their own weight, into the valleys below. These avalanches often occasion great destruction in their course.

58. Glă'ciers, masses of ice, or of ice, snow, and water, are remarkable appendages of the snow fields. They appear like frozen torrents hanging upon the sides of mountains, and extending from the higher summits into the lower valleys.

59. The size of glă'ciers sometimes amounts to fifteen or twenty miles in length, and three miles in breadth, the thickness at the lower portion varying from eighty to one hundred, or even two hundred feet. The front is melting, while above it accumulates and is consolidated; hence it is moving along the ground, advancing down the mountain slope, faster or slower, according to the season and the degree of heat.

60. VOLCANO. This is a term denoting a peculiar class of mountains emitting from their summits or sides melted mineral masses, with columns of flame, smoke, and ashes. Their general form is conical, with a hollow at the summit, called the crater, or cup.

61. The volcanic mountains are either continuously active, or intermittent, or extinct. Stromboli, one of the Lip'ari Islands, is an example of the active; Mount Etna, on the Island of Sicily, the intermittent; and the Isle of Päl'ma, one of the Cana'ries, the extinct, or third kind.

62. EARTHQUAKES and VOLCANIC ERUPTIONS are undoubtedly phases of the same phenomenon. Earthquakes are most abundant and violent in countries which surround or lie between volcanic districts. No phenomena are so terrible ample. Valleys when narrow and difficult of access. 56. Permanent snow and ice. — 57. Avalanches. -58. Glaciers.— 59. Their extent and progress. 60. Volcano; general form.-61. Classes and examples.-62. Earthquakes;