perceive a power at work sufficient to produce in time a continent of uprise and surface-irregularity as remarkable as any of those that now form the themes of our science. It is thus that geology and geography trace a causal connection between mountains now in course of elaboration and those that belong to tertiary, secondary, and primary eras; and, though now unable to determine the law that regulates their position, may yet, in this way, approximate to its expression.

In the mean time, and for the sake of reference, the mountains of Europe have been arranged into the British, Iberian, Alpine, Scandinavian, Uralian, and Caucasian systems; those of Asia into the Western, South-Eastern, Eastern, and North-Eastern; and those of Africa into the Atlas, Abyssinian, Guinea, Cape, and Eastern systems. In the New World the mountains of North America are usually arranged into the Eastern or Atlantic system, and the Western or Pacific; while those of South America are distinguished as the systems of the Andes, of Parimè, and of Brazil. As to the table-lands, the more important and better known in the Old World are those of Castile, Switzerland, Bavaria, and Bohemia in Europe; and of Armenia, Arabia, Persia, Tartary, Mongolia, Tibet, and the Deccan in Asia. In the New World those of Bolivia and Brazil are the most notable in South America; while in North America the only similar tracts deserving of notice are the table-land of Mexico and the desert uplands of Utah and Oregon.

In whatever form the highlands of the globe appear, whether as linear mountain-chains or as broad-spreading plateaux, they exercise most important influences on climate, and consequently on the distribution of plants and animals. In the torrid zone they afford the climate and produce of temperate regions, and in temperate zones they assume the characteristics of polar latitudes; while everywhere they are the great gathering-grounds of glacier, stream, and river-dispensing their stores to the thirsty lowlands in moderated but never-failing supplies. It must be observed, however, that mountain - chains which run in a latitudinal direction become more certain barriers to the dispersion of plants and animals, and better boundaries between nations, than those that run in a meridional course-the former severing, as it were, the zones of temperature that lie on either side, the latter connecting several zones, the warmer by their lower heights, and the colder by their greater elevations. A temperate flora or fauna may range almost from one end to the other of the Andes; whereas the life north and south of the Himalayas is as much apart as though they existed in different continents.

To the student desirous of following out more fully the study of the mountains and mountain-systems of the globe, and the causes concerned in their upheaval and formation, we may recommend perusal of the various 'Memoirs' of Von Buch and Elie de Beaumont, Hopkins's 'Researches in Physical Geology,' Daubeny's ' Treatise on Volcanoes,' Scrope on 'Volcanoes,' Mallet's 'Seismology,' the chapters on Igneous Formations in Lyell's 'Manual and Principles of Geology,' and Humboldt's 'Personal Narrative;' for descriptions of special ranges and their respective phenomena, such works as Hooker's 'Himalayan Journal,' Forbes's 'Glaciers,' Tyndal's Alps and their Glaciers,' Humboldt's 'Narrative,' Fremont's 'Rocky Mountains,' &c.; and to those curious in the matter of mountain measurements, the tables appended to the Physical Geographies of Sir John Herschel and Mrs Somerville will supply the desired information.

6

VII.

THE LAND-ITS LOWLANDS.

Plains and Deserts.

87. As the higher and more irregular portions of the earth's surface consist of mountains and table-lands, so the lower and more level consist of plains and valleys. The one set of features counterbalances, as it were, the other, and thus contributes to that variety of aspect so pleasing in the landscape, and so indispensable to diversity in its animal and vegetable productions. In a general view, mountain and plain are the direct antithesis of each other, -the former high, cold, rugged, and inaccessible—the latter lowlying, warm, fertile, and everywhere open to the dispersion of plants and animals, and to the settlement and growth of human society. Though the term plain is usually applied to level expanses of no great elevation, and is apt to be associated with verdure and fertility, yet several of the great plains of the world are considerably above the sea-level, and present every variety of surface, from green grassy flats to deserts of shingle and loose shifting sand. As mountains were the results of volcanic upheaval continued through indefinite ages, so plains and valleys are the undisturbed portions of the earth's crust, and in most instances represent the beds of former seas, and the silted-up sites of lakes and estuaries. Not only does their general contour convey this impression, but their soil and subsoil reveal their origin, and point to a time when large expanses of ocean occupied the areas of the present plains, and shallow estuaries and chains of lakes the sites of our alluvial valleys. Bearing in mind this origin, it will help to explain certain appearances of soil and surface, and enable us to account for certain distributions of plants and animals that might otherwise remain inexplicable.

88. In treating of the low level tracts of the land, the terms plain and valley are sufficiently general and well understood, and

are therefore the most frequently employed in geographical description. There are others, however, which refer either to some peculiarity of surface and condition, or are of local origin, and these it may be useful at this stage to explain. Thus the term prairie, though simply the French word for "meadow," is usually applied in a technical sense to the open, slightly undulating, grassy plains of North America; llanos are the river-plains of tropical South America, alternately covered with rank vegetation, and reduced to a desert by periodical droughts; selvas (Lat. silva, a wood), the higher tracts of the same region, densely covered with natural forest-growth; and pampas, the treeless but grassy plains of the Parana and La Plata. The term steppes is applied to the plains of northern Asia, generally covered with long rough herbage, but also partially wooded, and not unfrequently shingly and desert; tundras to the boggy, frozen flats of Siberia and northern Russia; and tarai to the belt of unwholesome jungle that lies between the plain of Hindostan and the Himalayas; Sahara is the long-established and familiar name for the great, arid, and sandy desert of northern Africa; while karoo is applied to the open flats in the southern region of the same continent, which are hard and arid in the dry season, but carpeted with grasses and flowers during the periodical rains. In Britain the terms dale and vale are usually applied to minor river-plains; strath, in Scotland, to any wide stretch of generally flat-lying land; and carse, to those level alluvial flats that occur in connection with existing estuaries, and which have evidently been reclaimed from their waters either by the ordinary process of silting, or by partial upheaval of the land. The term delta is also largely applied to the alluvial land formed at the mouth or rather mouths of a river, such as that of the Nile, which first received this name from the resemblance that the triangular space enclosed by its two main mouths bears to the Greek letter A or delta. Other terms than the above are

Nilotic Delta.

still more local and restricted in their application, and will be better explained in the text, or in the Glossary, to which the student should make regular and systematic reference.