The Ilanos, however, notwithstanding the apparent uniformity of their surface, furnish two kinds of ine qualities, that do not escape the observation of an atten tive observer. The first is known by the name Rancor ; they are real shoals in the basin of the steppes, fractured strata of sand-stonc, or compact lime-stone standing lour or five feet higher than the rest of the plain. These banks are sometimes three or four leagues in length ; they are entirely smooth, with a horizontal surface ; their existence is only perceived by examining their borders. The second species of inequality can be recognised only by geodesical or barometric levellings, or by the course of rivers. It is called Mesa, and is composed of small flats, or rather convex eminences, that rise insensibly to the height of a few toises.
The uniform landscape of the Banos; the extreme rarity of inhabitants; the Fatigue of travelling beneath a burning sky-, and an atmosphere darkened by dust ; the view of that horizon, which seems for ever to fly from before us ; those lonely trunks of palm-trees, which have all the same aspect, and which we despair of reaching, because they are confounded with other trunks that rise by degrees in the visual horizon ; all these causes combined, make the steppes appear far greater than they are in reality. The planters who in habit the southern declivity of the chain of the coast, see the steppes extend toward the south, as far as the eye can reach, like an ocean of verdure. They know that from the Delta of the Oronooko to the province of Vari nas, and thence, by traversing the banks of the Mela and the Guaviare, and the Caguan, they can advance three hundred and eighty leagues in the plains, first from cast to west, and then from to be yond the equator, to the foot of the Andes of Pasto. They know, by the accounts of travellers, the Pampas of Buenos Ayres, which are also Ilanos covered with fine grass, destitute of trees, and filled with oxen and horses become wild.
26. In mountainous and hilly country, funnel-shaped hollows of different sizes are sometimes to be observed. The smallest kind have been formed by the sinking of rocks, and are peculiar to certain formations. The others are circular valleys: a stream or river usually traverses them, and disappears by a subterranean canal. Hence it happens that these hollows arc sometimes filled with water, and at other times dry. The Lake of Cirknitz is an example of this kind of valley.
27. We obtain a very distinct conception of the sur face of the earth, by comparing together the different inequalities that have been described, and we arc much assisted in forming this conception, by attending to the course of the water over the earth's surface. We can, by means of the course of rivers, distinguish great por tions of the surface of the earth, which are termed river districts by geographers. These districts are generally very wide.and flat troughs or concavities, in which the main river occupies the lower, and its exit from the concavity the lowest point of the district. In good maps we can trace out these districts, by drawing lines along the points where the small rivers and rivulets of the district took their rise ; and thus we obtain the boundary of the river district.
In the high land, river districts form peculiar basins or concavities; and these sometimes form connected series. They are often contained in the mountain group, but more frequently without them ; but still in the high land. Thus the Vallais, which is a conca vity of this kind, lies between the Alps of Switzerland and Savoy ; and the vicinity of Geneva affords another similar example. The river district of the Rhine forms many basins of this kind, in its course towards the ocean. As long as it continues in the Alps, these ba sins are inconsiderable ; but they increase in magni tude as soon as it leaves those elevated regions. The basin in which the Luke of Constance is situated, may serve as an example. A second basin of the Rhine occurs in Backe, where it is increased by many lateral streams. It extends from Upper Alsace to Hundsruck, and the vicinity of Maycnce ; where the Rhine forces its way through a narrow rocky passage. The river dis trict of the Danube forms a basin in Swabia, several in Bavaria, and one in Lower Austria, but is nearly shut up at Presburg, which forms the entrance into the great valley or Hungary. At the lower extremity of Hungary, the river is again forced to seek its way through a narrow rocky channel at Orosova, which is the only opening from Hungary into Wallachia. It now con tinues its course through Wallachia, and at length falls into the Black Sea. We have a continuation of these valleys or basins, although still filled with water, in the Black Sea, Sea of Marmora, and Mediterranean. This latter fact is particularly interesting, as it leads to inter esting considerations in regard to the former state of such basins or valleys. Bohemia affords another ex ample of this kind. That extensive country is a great circular valley, whose bottom inclines towards the only opening of the valley, above Konigstcin, through which the river FAe issues, carrying with it nearly all the water that falls on Bohemia. Immediately below this narrow Cocky outlet, there is another small circular valley, which extends from Konigstein to Pirna. At Pirna it is nearly closed up, the liver forcing its way through a narrow rocky opening, and at length it en let's a very beautiful valley, in which the city of Dres den is situated. This valley, as we approach Meissen, is further clown the Elbe, becomes narrow, and the river again flows through a rocky channel, until it escapes into the low country, through which it winds and traverses the flats of Lower Saxony, and is at length pouted into the North Sea at Cuxhaven. The river Don, in Aberdeenshire, also passes through seve ral circular or inclosed valleys, in its course to the ocean. At its estuary, the rocks confine it to a nar row channel; but on ascending on it for about a mile, the hills recede from it, so as to form a considerable extent of country on each side. About luverury it again appears to flow through a channel ; and still farther up it flows through anotner spacious valley. This valley continues for a considerable extent ; it at length contracts, and the river flows through another rocky channel. It continues in this channel for a con siderable distance, until it again flows through another wide valley.