of Asia Minor, and Hauran, Iceland, parts of the great American chain, parts of the Sunda chain, the South Sea Islands, and Bogdo-Oola, and its range of extinct volanoes in the Thian-Shan chain. But other forces besides fire were competent to form mountains and plateaus, to spread layers of clay and sand and various deposits at the bottom of the sea, afterward to harden into strata of rock. In contradistinction to plutonic formations, these have been called neptunic, because formed at the bottom of the sea. The oldest of the neptunic or stratified rocks have been upheaved by the subterranean forces, and now are found in the elevated plateaus or mountain-ranges, still retaining, however, their unbroken irregularity of structure. Also, after the stratification has been complete, and plutonic acclivities have opened the seams in the earth of which I have already spoken, and molten masses have rushed up to fill them, fragments of the primitive stratified rocks have been caught up and raised, together with the molten masses, to the very summits of lofty mountains; so that the geologist finds fossils there more or less perfectly preserved, the stratified rocks which contain them surrounded by the plutonic rock upheaved from below the surface. Chalk layers full of mollusca and infusoria have been found by Humboldt and Von Buch on the very summits of the Andes, and corresponding with those which have been discovered by Ehrenburg in the deposits at the bottom of the sea. Other older and more recent oceanic deposits are found in their primitive condition at the bottom of the sea, or in very low places on the land. In such localities the surface of the earth is composed of horizontal or slightlyinclined layers or strata, of secondary formation, and whose origin in deposits from water cannot be denied. These are the beds of chalk, clay, sand, marl, gypsum, and other common substances; and these strata again have been overlaid with more recent accumulations, the result of diluvium or alluvium, continuing even up to the present time.* LOWLANDS. This variety of the earth's surface stands in the strongest contrast with mountain regions, or, in one word, with the highland form in all its modifications. The name lowland we apply to all those broad tracts which do not rise more than 400 feet above the level of the sea. The absolute elevation is determined from a section drawn vertically from the superior surface to the plane of the sea. Every comparison by numbers of one lowland plain with its more elevated surroundings gives only a relative result, as for instance, in comparing the valleys of one chain of mountains with those of a more lofty chain. Such relative lowlands may lie at a great elevation above the sea, as the vale of Chamouni, for example, at the north * In exact correspondence with the historic progress of upheaval is the internal and external aspect of the result. In direct connection with the extent, course, grandeur, and succession of oceanic and volcanic forces, and in constructing new geological formations, is the inexhaustible variety of structure, in respect to continuity and degrees of fracture, as well as the more or less rich prodigality of mineral treasure brought to light. The later formations-the masses injected to fill up huge chasms opened by volcanic pressure from below-are easily distinguished from the primitive formation. These courses are usually the depositories of minerals, which the great internal heat has apparently sublimed and crystallised, giving us our goldsand, rock-salt, and the precious metals. foot of Mont Blanc, is 3000 feet above the ocean-level. The two conceptions of the word lowland, which is common to elevated plains, as well as those at the sea's margin, are entirely different, and should be kept distinct, although they are very often confounded. We are to deal here with only the absolute, great, and generally diffused lowlands, in contrast with which the elevated valleys and plains just referred to may be considered as mountain table-lands and the rims of plateaus. We assume, as we did in judging of the two grades of plateaus, an arbitrary standard of measurement, and limit the rise of real lowlands to an altitude of 500 feet above the level of the sea. Great tracts of running plain, rising by so slight a grade as to be almost imperceptible, can be regarded only relatively as lowland, and, in a strict sense, belong to those regions of transition which fall more truly within the domain of highland or plateau. The word plain indicates the opposite of hill or mountain, but has nothing to do with the greater or less degree of absolute elevation, although it is often used as if it had. The lower limits of lowlands are sharply enough defined. They are the margin of the sea, towards which the slope usually becomes almost imperceptibly small. Often the expression is used, yet not quite fitly, that the lowland extends into the sea for some distance, and is found beneath the surface. Strictly this is the bottom of the sea, and does not fall under consideration in this connection. Many lowland plains rise so slightly above the sealevel, that they are not unfrequently submerged, and, in many cases, owe their existence to repeated overflows. They are the basins of old gulfs, as in the very slightly elevated plains of Caracas, whose whole shore is open to the influences of the great Atlantic current flowing from east to west; or as in the great Lombardy plain, which slopes at the same almost imperceptible degree toward the Adriatic. There are also some lowlands found in the interior of continents, and these, too, sinking below the level of the sea; but they are altogether exceptional, and only met with in two or three instances. They are called, by an accommodation of an algebraic term, negative lowlands. To them belong the region around the Caspian and the Aral Seas, and the much smaller tract comprising the Dead Sea, and forming the Jordan valley; besides, there is the Suez steppe, enclosing the bitter lakes between Asia and Africa; and possibly the Beledel-Jereed, in the western part of the Sahara; and the central part of Australia. To these it might not be incorrect to join those partial lowlands which have been rescued by human efforts from the sea; the marshes, for instance, behind the dykes of Holland, Schleswig, East Friesland, and at the mouths of the Vistula, the Weser, the Nile, the Ganges, and other rivers. The most extensive lowlands in the world are probably those which embrace Siberia, in Asia, and the Canadian and polar region of North America. Many great tracts, entirely inland, are in those flat districts covered by seawater which was once driven in by great storms, and now lies stagnant, resulting in inapproachable swamps and morasses. Yet, under the equator, there are immense lowlands, as, for instance, in the eastern Sahara, although this region is broken by strips of plateau, and is by no means that uniform lowland plain which it used to be considered. Northern Australia belongs to the same cate gory, and also those immense plains which reach from the Atlantic so far into the interior of Brazil, along the lower Amazon. By the time, however, that they reach the middle course of that river, they have acquired, though by imperceptible steps, a considerable degree of elevation—according to Humboldt's barometrical observations, and not reckoning certain limestone hills found there, from 1050 to 1200 feet. The plains of the middle Marañon are, therefore, true plains, but not absolute lowlands, and not to be identified with the great flat region at the mouth of the river, or compared with the real lowlands of Venezuela, which do not rise more than 200 feet above the sea a genuine plateau, which, level and broad as it is, is far more elevated than the Valdai plateau, in Russia. Almost all great river mouths are true lowlands—the Egyptian delta, the delta of the Ganges and the Indus for instance (the two latter being separated by the very moderate plateau (1000 feet high) between Delhi and Mooltan); to these we may add the delta of the Euphrates, the east shore of China, between the Blue and the Yellow Rivers, and Senegambia, between the Senegal and the Gambia. And in America, the same thing occurs in the Mississippi, Orinoco, Amazon, and La Plata, where the immense mass of water which these rivers send to the sea passes through lowlands of very great extent. In the Mississippi they extend from the mouth as far north as the confluence of the Missouri and the Mississippi, where stands St Louis, not 500 feet above the level of the sea. The prairies west of the lower course of the river rise rapidly, though imperceptibly to the eye, to the high terraces of Kansas, at Council Grove, varying from 1500 to 2000 feet absolute elevation, and then more rapidly toward the west, to mountain plains or plateaus, from 3000 to 6000 |