PART II.
It is the province of Hydrography to deal with the oceanic world; Geography proper concerns itself simply with solid forms. The Hydrography of the globe we must pass over, however. Aside from the fact that it would lead us into studies of the most protracted nature, it forms strictly one department of nautical science. Besides, there is the less occasion to speak of it here at length, that works of great excellence have been published, relating to that branch. We turn therefore to the land, and shall study the world of waters only so far as it exerts influence on the land.
By land we mean the islands as well as the continents, for, as remarked before, the difference between them is merely relative. To the land division of the globe, however, belong all rivers and the internal fresh water lakes, however large. The basis of difference does not lie in the fact that one part of the globe is water, the other part land, but in the fact that one is a tract of uniform evenness, the other of constantly varying surface, the internal rivers and lakes only being frills, so to speak, to the elevated region, and not sharing the sea level of the great oceanic mass. Uniformity of surface is then the chief characteristic of the sea; a lack of it, of the land. A mathematical level isa thing unknown on extended districts, and an approximation to it is very rare. Even the basins of former seas do not display a perfectly level bed. The plains of North Germany are characterized by this billowy rolling. The flats along the Danube, in Hungary, and along the Po, in North Italy, have really important deviations from a true level, though the eye is not able to discern them. Milan is four hundred feet above the Adriatic; but the eye does not discern that it is not at the center of a plain as perfect as the surface of the sea itself, and yet that plain does shelve gradually away till the Adriatic checks and defines it. Pesth is two hundred and fifteen feet above the ocean level, yet the gradual decline to the Black Sea is undiscernible to the eye. The immense plains along the Amazon, even the celebrated llanos on the Orinoco, which Alexander von Humboldt likens to inland seas of verdure, have a not insignificant slope from west to east. The middle point of these llanos near the City of Calabozo, about 100 geographical miles from the sea, he found to be 180 feet above the sea level; far lower indeed than Milan or Pesth, relatively, yet at a perceptible elevation. All of these plains were once the bottom of the sea; the Adriatic laved the base of the Apennines and the Cottian Alps, and the Atlantic swept westward over the llanos of the Orinoco and the Essequibo, having the Sierra de Venezuela on the north and the Sierra Parima on the south, till it was checked by the Cordilleras of Merida and Pamplona.
Depression and elevation, then, are the characteristics of the land. They are both measured from the level of the sea; their absolute altitude is reckoned from the imaginary sea level, extended over the whole globe. Their mutual relations to each other are determined from their relative heights. The absolute elevation above the level of theocean can be determined in a number of ways. If the heights to be measured are in the immediate vicinity of the sea, a simple system of triangulation will effect it. If they are removed from the sea, the difficulties are greater, and increase according to the distance from the sea. The heights of great inland mountains are determined by complicated operations with the spirit-level, protracted trigonometrical calculations, the unwearied and skillful use of the barometer, and constant appeal to the boiling point of water. The description of these methods falls within the province of Physics.
As the determination of the heights of the loftiest mountains could not be made before the appointments of scientific explorers have attained to a certain degree of accuracy and delicacy, the knowledge of them in former times was almost wholly relative. The inquiries of La Condamine, Saussure, and de Luc, in the Andes and the Swiss Alps, are almost the only ones to be trusted among those of the older observers. All unscientific travelers without accurate instruments confounded absolute heights with relative heights, and innumerable errors crept therefore into the earlier text-books. It is only within the most recent times that Hypsometry has attained to the dignity of a science.
To meet and counteract the errors alluded to above, and current in the loose language of popular speech, we shall use a new and indeed arbitrary terminology,—arbitrary because the data which mensuration will sometimes furnish are now, in part, wanting. We will divide the earth not relatively, but absolutely, into highlands and lowlands. The great districts often met, whose elevations are very moderate, we call lowlands. They are, for the most part, immense plains, varied but little above the level of the sea.The great districts which inclose mountain ranges we call highlands, and sometimes plateaus. True highlands can often embrace very extended and elevated plains, and these plains again may include hills and mountains. This does not affect their character as highlands, which lies in the fact of elevation rather than in more or less modified variation of surface. There may be vast variety in the physical manifestations of a great plateau district, entirely independent of the relative effects produced by the distribution of its surface into plains, rolling land, hills, and mountains.
In the lowlands there may exist hills to some extent, and these may even be combined in ranges, provided only that they do not violate the uniform characteristics of the district in which they are found.
The highlands are generally met with in the interior of the continents; the lowlands at the coasts. Yet there are exceptions to this.
In the transitions from lowlands to highlands there is great diversity. We can speak of three distinct bases of discrimination: a sudden and abrupt ascent; a rise in elevation so gradual as scarcely to be perceived; and a terrace formation. Yet in these there is a blending of one variety with another; there is no place sharply marked, where we can say that one form ends and another begins. There are constantly found modifications of these three transitional phases. The plains along the Indus and the Ganges rise sharply to the plateaus of Thibet The flat Pacific coast of South America is exchanged with equal abruptness for the highlands of Peru. The transition is a gradual one from the lowlands of North Germany, along the Baltic and the North Sea, through Saxony and Bohemia to the Bavarian highlands, north ofthe Alps. The Spanish highlands form a series of terraces, increasing in height from south to north. The immense plateaus of central Asia are also terrace formations, of diminishing elevation, as they advance to Siberia; so, too, are the eastern plateaus of Peru, falling off in altitude toward the plains of the Amazon.
Just as varied are the heights taken from the sea level of the leading plateaus. Yet they never rise to a point of elevation comparable with those of isolated mountain peaks or ranges. These attain, in no insignificant numbers, the height of 24,000 feet, while some ascend thousands of feet beyond that. In Mount Everest, of the Himalaya chain, the loftiest summit yet measured (29,000 feet) is found; although it may be that future investigations more to the south will disclose yet greater heights.
Continuous highlands or plateaus seldom attain an elevation greater than a half or a third of the loftiest mountains; the most elevated range in altitude, from 8000 to 12,000 feet above the sea level. On an average, they lie about 4000 to 5000 feet above the sea. We take the last height as a convenient point of demarkation between the two classes of highlands—those of the first and those of the second magnitude. It is an arbitrary point, of course, and the division there must remain, without a natural base to rest upon, till more results in Hypsometry shall have determined the real point of average between the combined lowlands and the combined highlands of the earth’s surface. Meantime this division will be of great service to us in enabling us to bring into a definite and appreciable classification many facts which would otherwise not be so well understood in their relations.
By plateaus of the first class, we mean those high, continuous plains which lie at the elevation of more than from 4000 to 5000 feet above the sea level. The extreme height to which such plateaus rise is a fact yet to be ascertained. At an elevation of from 4000 to 5000 feet the highlands of the first class merge into those of the second. The point of transition is, of course, very difficult to fix with precision.
The high plateaus of Asia rise more than 14,000 feet. They inclose the head-waters of the Ganges and the Indus. All central Asia is a vast congeries of highlands; but, as a body, they by no means belong to the most elevated of the globe. They are colossal in their length and breadth, but not in their uniform altitude. In the latter respect, they are far more varied than is generally supposed.
The plateau of Thibet attains, in its whole great extent of 1800 miles in length and 500 miles in breadth, an average elevation of 10,800 feet above the sea level. In some cases it rises, of course, much higher, as, near the holy lake Manasarowar, for instance, where it is 14,000 feet above the sea. Others sink, as at Ladakh, in Little Thibet, to an altitude of about 9000 feet; so, too, Gertope, in the region remarkable for its goats and the rich shawls manufactured there, and Shiffke, are about 9804 feet above the sea. The plateau of Great Thibet, east of Lassa, the capital, and north of the Upper Brahmapootra or Yam-Dzangbotscha, is 9000 feet in elevation. There are also districts filled with mountain groups of great heights, but where the depressions sink to the level of the valleys of the Indus, Sutlej, Brahmapootra, as low indeed as 5460 feet,as at Cashmere, so that there is no lack of diversity in the great plateau of Thibet.
The plateau of Mongolia, or more exactly the desert of Gobi, can be ranked only on its lower edges, where it touches the Chinese frontier, as of the first class, although in extent it is twice as large as the great plateau of Thibet. Only near the north bend of the Hoang-Ho and near Peking does it reach an altitude of 8000 feet, and gradually sinks away as it advances toward the northern frontier of the Chinese territory, to 5100 feet, and farther north to 4000 feet; in the middle portions of the great table-land it is depressed to a height of 2400 to 3600 feet; it rises again at the head-waters of the Orkhon and the Toola to an elevation of 4620 feet, and falls off in terraces toward Kiakhta, near the northern boundary, where it is 1330 feet high, Selenghinsk, on the Selenga, where it is 1632 feet high, and Berch-Udaisk, where it is 1458 feet high, till it reaches Lake Baikal, 1332 feet above the sea level according to Humboldt, though Erman makes it greater.
Western Mongolia, (west of the meridian of Lassa, and west of the point where the Tarine flows into Lake Lop,) upper Bokhara, and upper Toorkistan were formerly considered to be a highland district; this is now subject to doubt. We shall discuss this further on.
Africa, too, has highlands of the first class, which, however, do not rise to the extreme height of the plateau of Thibet. As in Asia, so in central Africa, the old supposition of the existence of a plateau of colossal extent has been very much done away with by the more exact and critical modern investigations. The strip of territory lying between 4° and 10° north latitude has been demonstrated by Barth and Vogel to be destitute of highlands. The range of mountains announced as discovered by MungoPark, and called the Kong Mountains, is proved to have no real existence, and of course his statement fails of verification that that range is the northern limit of an elevated central plateau. The peaks which really do rise in the Kong territory form no continuous ridge; they are mere isolated groups of moderate height. Between these groups the lowlands continue toward the south, in an unbroken level, for an immense distance. How far south of the equator the central African plateau begins, is yet unascertained, for the snow-tipped peaks of Kilimandjaro and Kenia, discovered by Rebmann and Krapf, in the parallel of Mombas, 1° to 3° south latitude, are of immense height, it is true, but they do not demonstrate the existence of a plateau of the first class there. They rise out of table-land about 2000 feet above the sea level, which Krapf explored in the year 1849.
The Abyssinian plateau, on the contrary, takes rank among the most elevated on the globe. At 10° north latitude, south of the sources of the Blue Nile, lies Upper Abyssinia, or the kingdom of Shoa, with its capitals, Ankobar and Angolalla, 10,000 feet above the sea. Still farther to the north, in the ancient kingdom of Gondar, the German naturalist Rüppel ascertained the level of Lake Tzana to be 7000 feet above the ocean; to the southward of that the land rises to a still greater height, and northward of Gondar the plateau ascends to an elevation of 8000 feet, and mountains are met with 14,000 feet high. The terrace of Axaw on the east is 6650 feet above the Red Sea, which lies along its border.
To the south of Shoa lie the highlands of Kaffa and Enarea. All travelers agree in the statement that the inhabitants of that region are light-complexioned; and Johnson draws from this the conclusion that the centralplateau must rise to a height of over 10,000 feet to harbor people of a whiter hue than the dwellers of the less elevated localities. He saw a number of men of light complexion who came as far as from the fifth degree south latitude, not from mountain homes, but from high table-lands.
The plateau of South Africa rises at Lattakoo, in the country of the Bechuanas, north of the Orange River, to the height of 6000 feet. To the east, near the Snow Mountains, where the river has its source, it ascends to an altitude of over 10,000 feet. To the north, discovery had made great progress since 1849. There, on a broad plateau, Oswell and Livingstone brought to the knowledge of the world the existence of Lake Ngami, whose surface is 2825 feet above the level of the sea. The plateau which includes this lake at its place of deepest depression cannot be less than 3000 feet high, and at some localities yet higher. Still more to the north, at latitude 14° south, on the water-shed between the Zaire or Congo on the west and the Zambeze in the east, the plateau reaches an elevation of 5000 feet, according to Livingstone. Yet farther to the west, it rises still higher and takes undisputed rank among plateaus of the first class. There, at 18° south latitude, Galtne, on his journey of discovery in 1850, ascended the table-land of Ovompâ, a region of great natural productivity. On the way thither, going from south to north, at 21° south latitude, and therefore in the parallel of Lake Ngami, but about 500 miles westward, he ascended north of the Swakop River, the table-land of Demara, which he found to be 6000 feet high. From that plateau mountains, Koniati and Ometako, for instance, rise to a height of 8800 feet. From the Swakop River to Lake Ngami there is a continuous plateau.
The high table-land of southern central Africa does not then extend, as was once supposed, as far north as 9° north latitude, nor even to the later limit of 4½° north latitude; but at about 4° 10′ the distinction between lowland and highland seems to be sharply drawn, as the cataracts which terminate the navigation of the White Nile indicate. Here Father Knoblecher turned back in 1849, but he ascended the first of the mountains which there began to rise; his eye reached onward to mountains very near or on the equator. He says that those high mountains stand upon an elevated table-land. Thus, here at the source of the White Nile we have a plateau seemingly of the first rank. From such a plateau it is probable that the snow-capped mountains, seen by Rebmann and Krapf in the neighborhood of the equator, rose, which they thought, approaching from the eastern coast, held the source of the Nile.
At the northwest of Africa, too, at 10° north latitude, the territory which feeds the springs of the Senegal and the Niger is supposed to be a plateau of great elevation and of great extent. But at present our lack of knowledge prevents our attaining certainty regarding it. No thorough system of measurement has been yet applied there.
America possesses a number of plateaus of the first class. To the most prominent of these belong the ones which were first thoroughly studied by Alexander von Humboldt. It is to him that we owe our first accurate impressions of table-lands which, before his day, had been indiscriminately confounded with mountains, and had had no place assigned to them in the department of Geography. Doubtless, too, great prominence was given to plateaus at the outset; they were pushed into unseemly proportionto other matters as well worthy of investigation, but they have come into their true place, and now only wait the development of new facts regarding the size and height of some, to be properly understood and appreciated.
The measurements made in North, Central, and South America give the following results; much more complete, it may be remarked, than the results yet gained in Asia and Africa.
To the plateaus of the first class belong in America, at latitude 0°, the plain of Quito, almost 9000 feet above the sea, (Los Pastos in the north being near 11,000 feet,) and to the south, at 17° south latitude, the plateau of Upper Peru. Here the great Lake Yiticaca is found, 12,000 feet above the sea; eastward of the lake, the table-land rises yet higher, and at Alto de Toleda it is 14,000 feet in elevation, as high as the highest part of Thibet. At 20° south latitude, south of Lake Yiticaca, is the City of Potosi, whose streets are 12,822 feet above the Pacific.
In Central America is found, at 20° north latitude, the extended table-land of Mexico, 500 miles wide, rising to a height of 7000 feet, and farther to the north, in New Mexico, the plateau of Santa Fé, 35° north latitude east of the Rocky Mountains, and 7100 feet above the sea. The table-land on the west side of the mountains, and toward the Great Salt Lake, is undoubtedly just as elevated.
Europe and Australia are wanting in plateaus of the first rank, and in general the whole immense flat northern districts of the globe, though we are not yet quite familiar enough with the extreme north of America to speak with entire confidence regarding it.
Elevated plains which are at once continuous and bounded by a definite line of demarkation, and which do not attain an altitude of more than 4000 or 5000 feet, are considered plateaus of the second class. They are far more general over the whole earth than plateaus of the first class; in every one of the great divisions of the globe they appear in the utmost possible diversities of elevation, sometimes so gradually ascending that the lowest limit is hardly to be perceived. This makes it not only expedient but necessary to assign to plateaus a fixed though arbitrary system of classification, for without it we could attain to no thorough view of all their relations. This general system must afterward be confirmed and justified by protracted special investigations.
That not all the vast plains of Central Asia, from Thibet to the Altai Mountains, and from the Belur range to the Chinese Gobi, belong to the first class of plateaus, has been demonstrated by the Russian measurements, made by Fuss and Bunge in 1832, between Lake Baikal, Kiakhta, and Peking, and rendered highly probable by the investigations of Klaproth, Humboldt, and Zimmermann. Toward the northwest the plateaus generally sink from the moderate elevation of the Middle Gobi, 4000 feet, to Lake Baikal, 1332 feet above the sea, Lake Zaison, not 1000 feet above the sea, and the border of the plateau at Choimailocha, the Chinese frontier post on the Siberian line, 1000 feet above the sea, then to the lower border of the plateau of Bookhtarminsk (936 feet) and Semipalatinsk on the Irtish, (708 feet,) where the great Siberian plain begins. In the valley of the Tarim and of Lake Lop, pomegranates and grapes thrive, and cotton, which hasbeen raised of an excellent quality in Eelee, is found at a height of from 1200 to 2000 feet. And in contrast with the great arctic plain of Northern Asia, not 500 feet above the level of the sea, this central plateau will take its place as distinctively of the second rank.
The plateau of Persia lies on the border of both classes; for while the central portion touches 4000 feet, some parts rise much higher and some sink much deeper than the normal point. These balance each other, and the average is about the maximum elevation of plateaus of the second degree.
East of the Persian plateau lies the plateau of Cabool, 6000 feet above the sea. On the northern edge of Afghanistan is the plateau of Bamain, 7500 feet in elevation. More to the south is the high plain of Candahar, being 3500 feet, and the City of Candahar, 3264 feet above the sea. The plateau of Kweltah west of the Bolan Pass is 5220 feet. Still farther to the south is the great plain of Beloochistan, 7000 feet, with the City of Kelat, 5418 feet above the sea.
In the central part of the eastern Persian plateau in ancient Gedrosia, Drangiana, and Parthia, and Lake Zareh, the depression is the lowest. At Lake Zareh the elevation is 2100 feet; at Herat, more to the north, 2628 feet. In West Persia, on the meridian of the Caspian Sea, it rises higher; on the northern edge at Teheran it is 3672 feet; at Schabred, southeast of Astrabad, it is 4000 feet; at Kasbin, west of Teheran, it is 4000 feet; and at Samegon, 5700 feet. The lowest depression at Com and Kashan is not 2000 feet above the sea. Toward the northwest Persia thrusts up a short arm into the adjoining territory of Armenia. This is the highland of Ayerbaijan, Zoroaster’s “Land of Fire.” This connecting plateau of7000 feet elevation belongs to the first class. To the west of this the plateau of Armenia extends in varying range of elevation, from that of Lake Van, 5124 feet, to the plain of the Aras, (the ancient Araxes,) on which the double cone of Ararat rises to a height of 14,656 feet. But the table-land at the northern base of Ararat, the site of Erdschmiazin, is only 2860 feet high, Erivan a little higher, and Erdzeroune, on the plateau of the Taurus, the plain of the Upper Euphrates, 5730 feet.
The plateaus of Asia Minor embrace wide plains extending through the whole of the country, at an elevation toward the east, in ancient Lycaonia and Cappadocia, of 3000 feet, and sinking toward the west to 2000 feet.
To the plateaus of Armenia and Lycaonia, Strabo, whose home was there, and who carefully studied them, gave the expressive name of ὀροπέδια,i.e.mountain plains, a term which corresponds remarkably with our word plateau, but which, as Humboldt has remarked, was not of much use among the ancients. Strabo, however, directed attention also to the Oropedia of Sicily and India.
In India, Deccan displays similar formations, which rise gradually from south to north in Mysore, in Poonah of the Mahrattas, and in the table-land of Vindhya and Malwah, to 2000, 3000, and even 4000 feet. Deccan enjoys an admirable climate and the richest abundance of all natural productions. China too must have plateaus, for the Chinese wordyouenindicates very clearly a large elevated plain.
In Arabia the plateaus of the second class are largely found, and their height ascends from north to south, instead of from south to north as in Deccan. The Syrian Hauran is 2000 feet high, the plateau of Damascus 2200 feet, the plateau of Taif, above Mecca, 3000 feet, the plateau of Sapaa, in Southern Arabia, 4000 feet.
In North Africa that portion of the great Sahara which has heretofore been considered a low plain, lying between Tripoli and Lake Tchad, has been ascertained by the German explorers, Overweg and Vogel, to be a table-land of the second class, ranging in elevation from 1000 to 2000 feet. It begins at the Chorean plateau (2000 feet) in the south of Tripoli, and sinks to an elevation of 800 feet in the neighborhood of Lake Tchad. The average altitude is about 1500 feet. This moderate elevation of Sahara corresponds with the equally high plateau of Cyrenaica, 2000 feet.
The Atlas plateau, in the northwest of Africa, rises to a greater height—2000 to 3000 feet; the upper course of the Draa, near the Sahara, being 3000 feet; the high, broad table-land on which Timbuctoo lies, according to Renon’s measurement, is 1500 to 1800 feet above the sea.
In south Africa the low, or rather the moderate plateau, which borders the district of the Bechuanas on the north, rises, as it advances toward the lower rim of Africa, at Cape Colony, to an altitude of 3000 feet.
America has many plateaus of the second range of elevation, but her highlands of the first class are so imposing in extent, as well as in elevation, that they have been more carefully observed than the table-lands of the second class.
Along the eastern slope of the Andes, on the same parallel with the great plains of the Orinoco, the Amazon, and the La Plata, these plateaus extend, touching the base of the mountains, and appearing rather as terraces, or vast plains of transition, from the highlands to the lowlands, than as independent forms. Where Alexander von Humboldt measured them, west of the low plains of the Amazon, he found their height, measured from thesea, to range from 1050 to 1200 feet; he describes them as having the appearance of vast plains, and as differing from the lowlands of the Amazon only in their greater elevation; their slope toward the narrowing of the Pongo de Mauseriche being too slight to be appreciable.
Between the threefold forks of the Northern Andes, Humboldt ascertained the heights of ten plateaus, extending as far as the plains of Orinoco, and called by the various names, according to their elevation—Tierras templadas, or temperate districts, Tierras calientas, or warm districts, and Tierras frias, or cold districts—varying in height from 1800 to 6600 feet, the highest belonging clearly to the first class of plateaus.
The mountains of Brazil are interspersed among plateaus of the second class. The Brazilian mountains are not true ranges, but lie in groups, their height varying from 2700 to 5700 feet, and between them are the vast elevated plains, called Campas, which are true plateaus of the second class.
The southern point of South America, south of the Rio Negro, as far as the Straits of Magellan, known as the plateau of Patagonia, is a true table-land of from 1200 to 1400 feet in height. It is composed of ragged strata of porphyry or of vast lava-masses, and has been explored by Captain Fitz Roy, in 1837, from the mouth of the Santa Cruz River to the snow-capped Andes in the west. The plateau diminishes gradually in elevation from west to east, till it touches the sea line.
In North America the broad plateau extending through Northern Texas and the Indian Territory, and lying on both sides of the Arkansas River, increases in elevation gradually from St. Louis, on the Mississippi, less than 500 feet above the sea, to Santa Fé, on the upper course of theRio Bravo, 7000 feet above the sea. It ascends so slightly that the rise is imperceptible to the eye, the broad plains there taking the name of prairies. St. Louis is 420 feet in absolute elevation; the eastern Arkansas plateau 1500 to 3000 feet; the high western Arkansas table-land from 3000 to 7000 feet, where, at the point of greatest altitude, lies the City of Santa Fé, in the Territory of New Mexico, 7047 feet above the sea. This broad, sloping tract reaches out to a great extent at the north, crossing the Missouri, and embracing the colossal North American lakes. Lake Huron and Lake Michigan, about 578 feet deep, and Lake Superior, 627 feet deep, lie in vast hollows in that great continuous plateau, which extends into the British Possessions, rises again to 800 or 1000 feet in elevation, and is rocky and craggy, yet not enough so as to take the name of a mountain chain, but simply to form a clearly-marked water-shed, which Fremont and Nicollet have measured.
In Australia and Europe plateaus of the second grade of elevation are not wanting. In Australia, however, they are limited to the triangular district in the southeast, which has become the place of settlement for the chief English colonies, and which, bearing the name of King’s Table-land, rises to a height of 2500 feet, and occupies the largest area of all the Australian table-lands.
In Europe this physical feature is displayed most distinctly in the Spanish plateaus, which occupy by far the largest proportion of the entire peninsula. Madrid lies on one of these plateaus, at a height of 2100 feet, five times as high as Paris, on the Seine, and as high as Innspruck, in the very heart of the Tyrol; Toledo, in the valley of the Tagus, is 1734 feet above the sea. The average elevation of New Castile, the central part of Spain, is2000 feet. Old Castile, which borders it on the north, separated from it by the Guadarrama ridge, is about a thousand feet higher. Burgos, in the center, is 2700 feet above the sea; Segovia, to the south, 3100 feet. The average elevation of Old Castile is 3000 feet.
Then comes in natural order the Bavarian plateau, in southern Germany, ranging from 1500 to 1600 feet high, a broad table-land, on which lie Munich and Augsburg. It extends along the course of the Danube from west to east, from Lower Switzerland to Ratisbon.
According to the mean measurements of Humboldt, the lower plateau of Auvergne, in southern France, is 1040 feet in elevation; still less in altitude (840 feet) is the plateau of Burgundy and Lothringia, between the Vosges and the Ardennes. Limousin, Aveyron, la Forez, Monts, and Côte d’Or are plateaus.
The plateau of Lothringia, whose mean elevation is 648 feet, lies between the Rhine and the Moselle. The plateau of Luxemburg extends northward to the Eifel, where Prum lies, and to the Ardennes, where Malmedy, Eupen, Namur, Liege, and Aix-la-Chapelle lie.
In Middle Germany, a series of plateaus of the second grade begins in Upper Hesse, and extends eastward, crossed by mountains and valleys, traversing Upper Silesia and Galicia, and running along the northern side of the Carpathian Mountains to Podolia, on the Dnieper, thus embracing a strip extending through the larger part of central Europe.
A line of plateaus begins still farther to the north, at the low hills of Jutland, crossing Holstein, Mecklenberg, the whole southern edge of Pomerania, and extending to Lithuania and the Valdai Hills. It is characterized by a band of inland lakes, whose basins it incloses, and iscrossed by the valleys of the Oder, Vistula, Niemen, and Duna. It has been called the Pomerania lake country. In the hollows where the lakes lie, (whose surfaces are, at the highest, not more than 300 feet above the sea,) and yet more in the depressions, where rivers break through, the level descends to as low a point as that of the great plain of Central Europe; but at other places it rises to an elevation as high as 500 feet, and so touches upon the limits of plateaus of the second range. Many parts of this broad upland may possibly be formed of shifting sand dunes which have been gradually piled up along the sea line. The plateau reaches its highest point at the eastern end, in the Valdai Hills, where it averages 1000 feet in elevation. The highest point is 1100 feet. East of the Volga, which rises at the eastern side of these hills, the plateau falls off by imperceptible steps, till it is lost in the great Russian plain.
In the peninsulas of Southern Europe, as in the Morea, (2000 feet,) and in the Crimea, (800 to 1200 feet,) the plateau again appears in not insignificant proportions.
The lower range of plateaus, it will be seen, is far more frequently met with through all parts of the earth than the higher, yet both combined occupy a larger share of the surface of the globe. We can designate them as sharply defined and broadly massive elevations, in contradistinction to the long, narrow, and broken masses which have received the name of mountain chains. The latter have too often been confounded with the former and have received from geographers a treatment disproportionately full in relation to their claims. The plateau has been until recently an almost forgotten geographical element. Humboldt restored it to its rightful place; by many hundreds of measurements he has accurately settled its form, its effect onclimate, on isothermal lines, on agriculture, on the physical and moral life of nations, and even on the course of human history.
In closing this attempt at a general consideration of plateaus, I must confirm the reproach which Humboldt has cast upon most geographers of this day for their abuse of the word plateau. And I must at the same time admit that it is justly due to some parts of my own “Erdkunde,” where I have considered the plateau systems of Central Asia and Africa. When I wrote the pages of that work, thirty and more years ago, there were no scientific measurements then made of those regions, and the general ignorance led to a premature generalization, in which I used the ascertained features of the New World as probably in analogy with the unexplored center of the Old World. This use of really untrue analogies was carried by others to great lengths, and choratographers went so far as to depict the country according to the hypothesis of those who had written at first hand, and after using all the lights then existing, but who had never supposed that what they had indicated in general terms, would be afterward made so definite and real to the public eye. Those untrue statements of my own, I must leave however just as they are, and rejoice that the great advance of science has led to the accurate knowledge of the great plateaus of which the civilized world then knew but little. One word more: I set the lower limit of plateaus of the second grade at 500 feet, lower therefore than the great master in Physical Geography set his.
“Elevations of the soil,” says Humboldt, “which do not display a marked difference in climate and vegetation from the country around them, are not rightly called plateaus.” His meaning is, that the name does not relate toabsolute height measured from the sea, but harmonious climatic relations existing between contiguous districts, one of which is more elevated than the other. Highland and lowland are therefore to him words of unfixed meaning, if they do not stand in the contrast of height, climate, relief, and rates of temperature. Humboldt therefore did not consider the depression of Central Asia, at the Taringol, as a plateau; and table-lands from 200 to 1200 feet in absolute elevation,i.e.from the sea level, are passed over by him as not worthy of the same name which he applied to the plains 6000 to 10,000 feet above the sea.
Dealing as I do with the elementary features and the physical contrasts of countries which for the most part are now thoroughly explored, I prefer, for the purpose of elucidating the subject of Physical Geography, to consider the plateau as beginning at 500 feet above the level of the sea. By comparing the plateaus of both hemispheres it is not difficult to deal with a variety of features, and to make a number of discriminations which, without an absolute standard, it would be impossible to make.
We pass to the consideration of the much more varied and more imposing characteristics of mountains.
Mountain lands cannot, in the strict use of language, be compared with plateaus, except in way of contrast, because they are not uniform, broad, and sharply defined tracts, but extend in a linear direction, having as their chief feature the longitudinal axis of the mountain chain. Groups of mountain ridges may be separated from each other, or may be united in any coherent way which does not make them continuous, and yet, despite the want of continuity, form a perfect whole.
Mountains, with their fissures, chasms, abysses, valleys, ravines, clefts, precipices,—in a word, their varied diversities of feature, broken through in every direction, the whole chain rent into fragments by these transverse breaks, are in direct contrast with plateaus. They have quite often a common range of elevation, which, measured from the sea level, is not unfrequently much greater than the districts lying at their base. Yet this relation is only incidental, it is not essential. There is no necessary connection between the height of the outlying plateau and the height of the mountain range. In Switzerland the mountains rise to the altitude of 13,000 or 14,000 feet; the country at the foot of the Alps is but 1000 to 2000 feet above the sea. Here the distance between the summit and the plateau at the base suggests no relation between them.
The distinctive characteristic of a mountain land is the height of isolated groups. Great differences of elevation within small distances characterize mountain regions; small differences within great distances characterize plateaus. The plateau depends upon uniform evenness of surface, or an approximation to it, over a large extent of territory. The mountain range is the exact opposite, the development of all kinds of extremes within a limited space, and the consequent individualization of the locality where it stands. Mountain lands cannot therefore be identified with the type of the highland and the plateau. The mountain chain has a character of its own, whether existing in unbroken unity, or subdivided into subordinate ranges, ridges, and spurs, and whether the summits are conical or sharply pointed,—whether also of moderate, medium, or loftiest elevation.
And high as mountains rise, their height is equivalencedby the depth of the depressions which form their valleys; the higher the mountain, the deeper the abyss which cleaves to the base. The immensely elevated peaks of the loftiest chains find their correspondence in the narrow ravines and the mountain lakes at the foot; the precipitous summits of the great American chain have their barrancos in the Andes and their cañons in the Rocky Mountains. The valleys are in natural contrast with the summits. They have just as little of the uniformity of lowland plains as the mountain tops have of the uniformity of elevated table-lands. They are infinite in variety, highly individualized, and always adapt themselves to the characteristics of the chain which conditions them. The mountain, too, has no uniformity in its character; it embraces within the smallest compass the production of all climes, and unites the characteristics of both highland and lowland. Mountain regions have therefore had a great influence in history and in the development of humanity, even greater than the more monotonous plateaus, which in general harbor nomadic races and give little encouragement to permanently settled people. For this reason the geographer cannot, like the geologist, classify high table-lands and mountains together; he cannot draw the same inferences from the plateau as from the mountain range; to the geographer the plateau is not a lower type of mountain, but the two, in their relations to man and to history, suggest entirely different results and condition entirely different processes.
And yet it must be confessed that mountains do stand in intimate connection with plateaus of both classes, and that the transitions from the one form to the other are well worthy of study. Yet the present lack of correct measurements has made this little understood.
It is not the element of height alone which gives mountains their significance. There are many other features, which are little studied, yet of real import. It is, however, not a matter of indifference whether a chain thrusts up its peaks 1000, 5000, 10,000, or 20,000 feet, and the height has been made and will continue to be made a subject of careful investigation. In reference to height, we distinguish what, in a general sense, we call mountains,[3]into hills, mounts, and mountains of various degrees of magnitude. Yet the height of the highest range, in comparison with the diameter of the earth, is insignificant, only about ¹⁄₁₇₀₀, and the combined mass of mountains are of no more account in comparing them with the entire mass of the globe, than the roughnesses on the rind of an apple, or perhaps more exactly still, than those on the shell of an egg. The combined mountain systems in the world would not suffice, if transferred to the North and South Pole, to fill out the earth to such an extent that the polar and equatorial diameters would be equal.
In following out his profound scientific investigations, Alexander von Humboldt, in order to ascertain the center of the earth’s gravity, taking into account the existing elevations above the ocean level, was led to the conclusion that too great importance was formerly assigned to mountains in their relations not to the course of history, but to the earth as subject to mathematical laws. Very careful observations revealed the fact to him that all the mountains of France, if reduced to a level and spread out, would raise the grade of the whole country to a height not morethan 816 feet above the sea line. All the mountains of Europe, distributed in like manner, would raise the level to only about 630 feet. In Asia the same process would make the vast plain only 1080 feet high, in North America 702 feet, in South America only 1062 feet; while the mountains of the entire globe would raise the level to only 947 feet above the level of the sea. So insignificant are the combined mountain systems of the earth in respect to size, in comparison with the immense body on which they stand, though their importance is great when we regard their influence on the localities where they are found. Yet in this last regard, mountains deserve careful study, for they not only exercise and have exercised a great influence over nature and man, but they serve as our best key to open to our view the internal structure of the earth.
Some mountains, though of great height and broad base, like Etna, Vesuvius, Teneriffe, and many volcanoes, belong to no true mountain system; and even when they lie near together, and yet have no inner principle of unity, they are not spoken of as a chain or a range: they make merely a mountainous district. It is the repetition of the common type and the existence of a continuous valley which gives a right to use the names chain and range.
The linear extent and height of mountain ranges vary very much; no definite limits to these can be assigned. Yet there are few chains which are less than 25 miles long and 1500 feet high. Other features are necessary in order to determine the strict application of the word chain or range; one is a ridge-like or comb-like aspect; (that it should be a water-shed is not essential, although very common;) another feature is that the rock composing it should be of the same geological formation. Sand dunes, although occurring in regular and ridge-like uniformity,like those in Holland, and looking from a distance like a mountain chain, are not to be reckoned as mountain chains, though like the tells on the Syrian steppes and dunes in the Netherlands and along the Baltic coast, they sometimes rise to the height of a thousand feet. In South Germany and in the neighborhood of lofty mountains, such elevations are called mere hills; at the north foot of the Alps, yet greater heights are almost always called level land. In judging of the fitness with which the word mountain is used, it must always be remembered whether he who employs it dwells among the Himalayas or on the lowlands of eastern Europe; and in order to give any fixedness to the use of the word, it is necessary to take into account other physical characteristics besides height. By common usage, however, the Alps have become the standard of comparison for all the mountains of the world, mainly because, besides having their imposing height, they are found in the middle of the temperate zone; they are the most convenient to study of any great system on the globe. In respect to height, we divide these into four grades: the lowest from 2000 to 5000 feet above the sea; the next from 5000 to 8000; the next from 8000 to 10,000; and the highest from 10,000 on to the height of Mont Blanc.
Another standard might be found in the colossal Himalaya chain of Asia, and the Cordilleras of both Americas, which could easily be brought into unison with the Alpine chain of Switzerland.
The linear direction of a mountain chain, the axis of elevation as we might say, (so sharply hinted at in the very word mountain-chain,) brings out relations which vary not only according to the longitudinal direction itself, but to the lateral extent, the number of mountains, the situation,and the ramification of the chain. If the direction be a straight one, we can rightly speak of an axis of elevation. According to Humboldt’s measurements, this axis in the Pyrenees is 230 miles in length; in the Alps, from Mont Blanc to the Hungarian frontier, 515 miles; the Ural Mountains, 550 to 2042 miles; the Scandinavian Mountains, 1100 miles; the Altai Mountains, 9900 miles; the Kuenlun, 1600 miles; the Thian-Shan, in Inner China, 1700 to 2150 miles; the Himalayas, 1600 miles; the Yablonoi Chrabet, 550 miles; the Aldan, 400 miles; the Ghauts, 760 miles; the Andes of South America, 4400 miles; and the whole Cordillera of North America, 9200 miles. There is often much doubt about the true beginning and ending of a mountain chain, and judgments differ according as they rest on the fact of elevation or on the geological traces of upheaval where they begin to be manifest. Geographers are not agreed, for example, whether the Ural Mountains continue as far north as Nova Zembla, and whether one or two chains in America are to be spoken of as traversing the plateau of Mexico.
If there are parallel ranges, it is correct to speak of a transverse axis, running at right angles with the main axis. There is, it is apparent, a marked difference between simple chains and the accumulated parallel chains, where breadth is a prominent element, as in the Vosges, the Black Forest Mountains, the Fichtel range, the Hartz, the Ardennes. The parallel rows form a mountain system. Yet all great chains are made up of smaller ones, of groups at least, and so are mountain systems. Often the grouping is seemingly irregular, a lawless aggregation, but only because our knowledge is incomplete, and the law of arrangement concealed from us. This law is traced in the very geological qualities of the chain, not in the later form. Theouter form is often very deceptive, the very convulsions which indicate the surer signs having served to obliterate what we should suppose the most prominent marks. The present of mountains must often be studied in the light of their past. Orography must be interpreted by geology. But the geological surveys of the earth are as yet very imperfect; the outer form has often to be accepted as the only guide. Orography and geology are two sciences which now go on hand in hand.
In the simple mountain chain it is easy to discriminate between the parts which make it up; the base is easily ascertainable and the ascent to the comb-like ridge is readily traced; the eye does not fail to see the relation between the special prominent heights and the chain from which they rise, and to trace the manner in which spurs and outlying mountains are connected with the main chain. Small isolated collections of mountains are especially valuable as elementary studies, for they always have a unity of their own. And all the greater and well-known chains are made up of smaller, simple chains, whose connection and mutual relations are, however, sometimes exceedingly difficult to trace. But the character of the whole is not sometimes ascertainable with this preliminary knowledge of the parts.
The true base of a mountain chain, the line of periphery, in consequence of the general unevenness of the adjacent country, must be ascertained by very exact measurements with the level. The geologist does not begin with this step, he strikes deeper, and seeks the place where the structure diverges from that of the more level land lying near; and, in the search after the basis of structure, he discovers the unity of the range from the foot to the summit. The whole geological district which has been upheavedinto mountains, Leopold von Buch found to be generally ellipsoidal in form, the longer axis being far more prominent than the shorter one. The axis of most mountain chains is, then, the longer axis of an ellipsoid. The Swiss Alps display about a dozen such ellipsoids, of different characteristics, and arranged according to no perceptible law of harmony. Each is developed from its own base, as the trunk of a tree grows out of its root. These separate bases lie contiguously, but the peaks which shoot up are widely sundered. The forms of the mountain groups resulting from this are, of course, various. Some of them I will briefly characterize.
1. The longer axes of the subordinate chains may run in parallels, as in one portion of the Swiss Alps, the Jura, the Ural Mountains, the Mexican Cordilleras, and the Himalayas.
2. The chains may diverge or converge. The Alps diverge at the east, and the forks run northeast and southeast respectively; the Rocky Mountains, toward the Arctic regions, divide into from five to seven diverging chains. Converging ranges may come together at varying angles, and these can mass themselves into confused mountain knots, the summits of which soar to amazing heights, as the West and Middle Alps do around Mont Blanc. Alexander von Humboldt distinguishes five of these mountain knots in the Andes, Porco, Cuzco, Pasco, Assuay, and Los Pastos, whose construction, carefully studied, he considered, gives the key to the structure of the whole chain. Side chains often display this knotted form, as in Upper Peru around Lake Titicaca, the three branches of the Ural, at the Irmel Tau, the Himalaya, Kuenlun, and Hindoo Koosh chains, in upper Afghanistan, and the ranges of Swiss Alps, which converge around St. Gothard. Yetthe convolutions which these mountain chains make at their point of convergence are never regular, never mathematically exact, but to be measured in sections, and the traces of a linear direction to be carefully sought with the compass. The whole has, to the eye, a labyrinthine appearance, and the law of structure is only ascertained, with exactness, by the geological features, the direction of the strata, and the like. The geographer must call in the geologist to help him solve his problems.[4]
3. If from some high central point the mountain ranges radiate in the form of a star, they form a new variety of system called, for convenience, by the name “star-shaped.” In volcanic mountains this configuration is common, as in Mont d’Or and in Auvergne. The southwestern Alps, known sometimes as the Sea Alps, the Ural at the Arctic Ocean, the Quito range of the Andes, are types of this form.
4. The ring-shaped system is in direct contrast with the last. It is found where mountain chains are arranged in a circle, inclosing a plateau of larger or smaller extent. There are two marked examples of this form in Europe: Bohemia and Transylvania. The ring of mountains around the former is made up of a number of ranges, which dovetail together at the ends, making a unit, but only a rude circle, speaking with mathematical exactness. The inclosed basin is only relatively a lowland; it is rigid with hills and low mountains, yet of such little importance,in comparison with the rim of peaks, that the common name, the “Bohemian Kettle,” has begun to have an accredited significance, and is stronger than the more loosely-used word Basin. Transylvania, too, partakes of similar characteristics. Its border consists of a number of minor ranges, of varying heights, up to 1800 feet; and the central hollow, which is much more strongly marked by hilly land than Bohemia, lies 2200 feet above the Adriatic. The ring-shaped system is one of the rarest met of all. They are, however, observed in abundance on the moon.
5. Just as rare is the form where ranges intersect in the form of a cross, those running, for example, from north to south, meeting those running east and west. As an instance of this, Humboldt cites the confluence of the Himalaya, the Kuenlun, the Hindoo Koosh, and the Belor or Belurtagh Mountains. The belt between 35° and 40° N. lat. is remarkable for its gridiron-shaped mountain system, the points of conjunction being marked by knots of peaks of colossal height. The most remarkable one of these is the lofty Pamir Pass, between 37° 30′ and 40° 5′ N. lat., and 18,000 feet high, known, historically, from the sixth century, and described by Marco Polo, as well as by the ancient Greek historians. The Persians dwelling in the neighborhood term it the Roof of the World. Elsewhere the same feature is observable, though on a scale of less magnitude. So in the Altai range at Lake Yetzkoi, in the western Swiss Alps, and in the porphyritic chain of Room-Elee, known to the ancients as Rhodope, and now as the Despoto Dagh. This gridiron-shape of some mountain systems seems to be the result of upheavals at different times, which necessarily occasions the most broken configuration at the point where a chain of more recent formation has been projected through one of older date.
The varying relations of length, breadth, direction, connection, and severance of mountain ranges give great diversity to them, and impart to every system a character of its own. To the features just indicated must be added vertical or precipitous descents, for the influences which they exert upon the possibility of man’s constructing mountain roads, are very great. The extent of these sudden depressions, or, more exactly, the relation which the distance from the base to the pass bears to the distance from the base to the summit, gives a key to the uses of certain mountains as adjuncts of civilization, and shows how some ranges rather than others may become the abode of men, and produce marked effects on human culture and the world’s history.
I have before alluded to the comb-like structure of most mountain chains. The resemblance is more striking than may appear; for not only do the peaks correspond in general uniformity of height with the teeth of the comb, but the equally uniform height of the passes from the base corresponds with the uniform thickness of the solid part of the comb. The relation, however, of the distance from the base to the passes, to the distance from the base to the peaks, is widely various. Humboldt has estimated it in a few leading chains as follows:—
In the Alps and Caucasus the relation of the height ofthe pass to the height of the chain is as 1 to 2; in the Himalaya, Quito Cordillera, and Alleghany Mountains, as 1 to 1·8; in the Pyrenees and Cordillera of Bolivia, as 1 to 1·5. In the Alps, therefore, where the pass is only half as elevated as the chain, the communication is the most direct, and the least barrier is put to the purposes of man,—a fact of great import in relation to human culture. The Pyrenees are in direct contrast in this respect, the most unapproachable, the most sundering of mountains.
The position of mountain chains is a matter of the first importance in relation to the welfare of man, and the solution of many of the most important problems in history. Whether interior ranges like the Ural and the Atlas, or ranges connecting two seas like the Caucasus, or those like the Mexican Sierras, lying between two oceans, are most open to human approach and use, is a question which we will not here stop to consider; but it may be said that, whether situated in the relations just indicated, or whether they are meridianal ranges like the Ural, the Scandinavian chain, the Alleghanies, or the great Cordillera of both Americas, which extends from the tropical world to both polar zones; or whether they run in the same direction with the parallels of latitude, turning one side to the colder north, and another side to the sunnier south; or whether they assume a diagonal direction like the Swiss Alps, from southwest to northeast, or like the Caucasus, from northwest to southeast, is a matter of the first importance to ascertain. Of not less consequence is it to discover whether the chain is the edge or rim of a plateau, and can have, therefore, only a one-sided development, like the Himalayas toward the south, or the Anti-Taurus toward the north, because the existence of a plateau on the reverse side dwarfs the slant distance, andgives but a fractional part of what, without the plateau, would be open and clear.
As plateaus usually display this edge on both sides, the border has been aptly compared to a double ledge or rim, between the two sides of which the table-land lies, often tolerably high above the sea level. If these rims, like mountains, are not contiguous to the plateau; if they are separated from it by a valley of greater or less width and depth, running parallel with the edge, they form what Humboldt has called natural circumvallations. Of such the Altai range, on the north side of the Asiatic central plateau, is an example. The hollow between the range and the plateau just mentioned is partly filled with inland seas. The Caucasus may, in like manner, be regarded as the circumvallation of the American plateau, separate from it by the Koor and the Aras (ancient Araxes) rims. Yet in the Caucasus another modification occurs—a partial linking of the plateau with the range at the west extremity, by the connecting chain of the Moschic Mountains. In like manner the Pyrenees, in their eastern half, form a circumvallation around the north side of the Castilian plateau, separated from it by the basin of the Ebro, and forming a perfect ring around Upper Castile and the elevated province of Biscay.
In cases where a mountain chain rests upon a plateau, rising up in the very heart of it, its summits seem to be not high, although the basis, the true foot of the chain, may not be at the level of the plateau, but far lower, and such mountains may, therefore, be of great absolute height. The name superimposed mountains has been given to them. Such are the Kuenlun and the Thian-Shan ranges of Central Asia, the Guadarrama chain between Old and New Castile, and the Rocky Mountains in North America.These superimposed ranges often run near to and parallel with the rim or edge of the plateau, and seem to give it more completeness and breadth.
The geologist employs the word “sutures” to designate such forms, because they serve to unite those parts of a plateau which are at different heights above the sea level. He regards the mountains as rising to fill enormous clefts which great convulsions have rent in the earth, and as passing up, while in their fluid state, to a height above the level of the plateau, and bridging over the abyss. In this way our mountains which rest on plateaus seem to have been formed, as indeed is indicated by their geological structure.
The smaller plateaus display analogies kindred to those seen in the larger superimposed mountain ranges. The extinguished volcanic group of Auvergne rests upon the central plateau of southern France, which, according to Remond, has an average elevation of 1000 feet. The now silent volcanic group of the northern Rhine broke through the moderately elevated gray-wacke formation of that locality, and is, therefore, a superimposed range.
Mountain chains which diverge from plateaus and their serrated rims seem, nevertheless, to have some relation to them, even though they cannot be considered continuations of them. The Lebanon chain, for instance, which turns away at a right angle from the Taurus range, and runs southward through Syria and Palestine; the Lutznetskia and the Alatau Mountains, mineral ranges running from the Altai northward to Tomsk; the Yablonoi and the Stanovoi Chrabet ranges running to the northeast; the still unknown or little known range of Farther India, traversing the whole peninsula of Malacca, come under this head.
Completely unlike the groups thus far considered, are the isolated mountain systems, with uniform slopes on all sides, and with a roof-like form, distinguishable to the base. The mountains of Europe are mostly of this class—the Ural, Carpathian, Scandinavian ranges, the Alps, Apennines, and, in part, the Pyrenees. They give rise to rivers, not on one side alone, as do the Himalayas and the Andes; they are rich in resources of all kinds for the student and the economist, and thus make up in part for their comparatively unimportant dimensions. Their double-sidedness gives them a large influence on civilization, since rivers flow from them in all directions; while from the Himalayas they only flow to the south, and from the Andes to the east.
Plateaus and mountains, different as they are in appearance and characteristics, yet constitute, in their mutual action and reaction, and in their forms of transition from the one to the other, the highland system of the globe. Their relations are inexhaustible as Nature herself. We cannot study them without profit; but we can never come to a perfect knowledge of them all.
Like mountain systems, plateaus are not to be estimated in respect to elevated and superficial area alone, but in respect to form and position as well.
The American plateaus are elongated from north to south, but are of disproportionate breadth from east to west. The Asiatic plateaus, on the contrary, are not only of great length, but also of great breadth. The Spanish plateau, that of the Atlas system, and that of Asia Minor have their length and breadth nearly equal.
The surface of plateaus is exceedingly varied. It sometimesassumes the aspect of elevated plains, sometimes of rolling land, sometimes of horizontal strata of naked rock, as in Patagonia and the western Sahara. In one place it displays sand-hills, as in parts of the Gobi Desert; in others barren steppes, as in portions of Persia. Sometimes we find a gradual ascent of minor plateaus or terraces; sometimes single mountains rising out of the plateaus, as does Demavend; sometimes we find a chain of colossal peaks emerging from the heart of a plateau, like Thian-Shan and Bogdo-Oola. Sometimes there are plateaus broken up into crags and patches of level ground, like Persia; sometimes plateaus with deep valleys or river basins, like the plateau of Yoorkistan and Gobi, including the River Tarim, and reaching its greatest depression at Lake Lop, or, like the plateau of Afghanistan, including the River Hirmend and Lake Zareh; again, we have plateaus traversed by water-courses which forced their way in times of flood, and leave in the rainless seasons the traces of the former violence. Such are some of the less elevated plateaus of France and Bavaria.
Especially important are the combinations and groupings of plateaus, as well as their relation to adjacent lowlands.
In Africa the plateau form embraces the larger southern half of the continent. Low plains are, on the contrary, the prevailing form in the north, broken, however, by the Sahara, and the high coast plateaus of the Atlas range, and of Barca.
In Asia there is a vast central plateau with gradual declivities toward the east, toward Yoorkistan and Persia on the west, and toward Lakes Baikal and Zaisan on the north. On the south the descent is abrupt to the Indian lowlands.
In Europe there are, for the most part, scattered and disconnected plateaus of small size and little elevation, often passing by an imperceptible gradation to the other forms. The Spanish plateau is, however, a marked exception, and has the sharply-defined character of the northern African plateaus. In eastern Europe the central situation of the isolated Valdai plateau, whose elevation is very moderate, but 840 to 1080 feet, is remarkable, and is of very great influence in determining the hydrographical character of the great Russian lowlands. And in fact, the hydrographical influence of both mountains and plateaus is so great, that it is worthy of careful and special study.
The combinating and grouping of plateaus in different continents give rise to great contrasts, observable most distinctly in Asia and America.
Asia, with all its great internal depression from Cashgar to Lake Lop, yet displays such immense districts of plateaus, all ranges of elevation, low, moderate, and very great, that the very grandeur and extent of its colossal mountain chains are subordinate in comparison. Asia is the land pre-eminently of plateaus.
America displays, not in its central but on its western coast, the greatest chain of mountains on the globe, flanked by plateaus of great elevation, but of superficial area quite out of proportion to the length of the mountain chain, and to the extent of the lowlands of both the northern and the southern divisions. And while in Africa the regions of depression are in the north, and in Asia around the great central plateau system, in the Americas, both North and South, they are thrown into the eastern portion.
Australia, in perfect contrast again, is, with the exceptionof its southeastern corner, a vast tract of unbroken lowland. No diversity is possible there, no change in the condition of life, but a ceaseless uniformity of monotonous but prodigal gifts.
Is not the imposing grandeur of these harmonious, provisional arrangements for the use of man calculated to fill the soul with admiring wonder, and to lead us to suspect, above all this display of cause and effect, above all this working out of a manifestly preconceived plan, the existence of a great and active Being, who has planned and executed it all with higher ends and a loftier purpose than to satisfy the mere earthly life of man?