Guatemala is naturally divided into five regions - the lowlands of the Pacific coast, the volcanic mountains of the Sierra Madre, the so-called plateaus immediately north of these, the mountains of the Atlantic versant and the plain of Peten.
Besides the Bokovoi Khrebet several other short subsidiary ranges branch off from the main range at acute angles, lifting up high montane glens between them; for instance, the two ranges in Svanetia, which divide, the one the river (glen) Ingur from the river (glen) Tskhenis-Tskhali, and the other the river (glen) TskhenisTskhali from the rivers (glens) Lechkhum and Racha.Down all these glens glacier streams descend, until they find an opportunity to pierce through the flanking ranges, which they do in deep and picturesque gorges, and then race down the northern slopes of the mountains to enter the Terek or the Kuban, or down the southern versant to join the Rion or the Kura.
On the western versant of the Andes of Ecuador there are three river systems of considerable size - the Mira, the Esmeraldas and the Guayas.
It is formed by the confluence of three head-streams, one of which rises on the northern versant of La Sagra (7875 ft.), a mountain in Granada, while the other two spring from the Sierra de Segura, in Jaen.
The Shilka and the Argun, which form it, flow first towards the north-east along the windings of the lower terrace of the great plateau; from this the Amur descends, cutting through the Great Khingan and flowing down the terraces of the eastern versant towards the Pacific. A noteworthy feature of the principal Siberian rivers is that each is formed by the confluence of a pair of rivers.
The south-eastern like the northwestern corner of the island is watered by a considerable number of short mountain streams. The one great river of the eastern versant is the Kutei or Mahakan, which, rising in the central mountains, flows east with a sinuous course and falls by numerous mouths into the Straits of Macassar.
Oases.In the western desert lie the five large oases of Egypt, namely, Siwa, Baharia, Farafra, Dakhla and Kharga or Great Oasis, occupying depressions in the plateau or, in the case of the last three, large indentations in the face of limestone escarpments which form the western versant of the Nile valley hills.
Most of the rivers of the northern versant are comparatively small, as the island narrows into a kind of promontory.
The rivers of the southern versant are waters of capacious drainage, the basin of the Kahayan having, for instance, an area of z 6,000 sq.
The Kebbi, fed by many torrents rising in the eastern versant of the Mandara Hills, issues from the S.W.