along real tunnels or corridors fenced in by stones of different sizes, sometimes measuring 5o to Ioo cub.m. The granite there is of every possible variety, mostly in light shades, yellowish red or light grey, sometimes coarse-grained, sometimes fine-grained, but frequently also striped. From the point where we turned to the south-west, we found ourselves in a peripheral region, the valley being deep, wild, and narrow: we had not seen anything like it since we left the Tscharklik-su. All the valleys and glens that we came into contact with on the Tibetan highlands were less energetically excavated, the denudation products in their bottoms being pulverized into fine gravel, or usually sand and dust, while the mountains that border them are relatively of minor elevation and their sculpturing less accentuated. The glen of Tscharklik-su is on the contrary deeply cut; but then it belongs in a manner to a peripheral region, if we regard the whole of the Tibetan upswelling as a physicogeographical unit. Strictly speaking however this glen also belongs to the central regions with self-contained drainage, though in its particular case this character is of less importance. All the streams that descend from the Tibetan upswelling have carved out deep channels for themselves, not only in the south, the east, and the west, but also in the north, where the stream of the Tscharklik-su ends in the basin of Lop-nor.
Upon looking back up at the point where our valley turns to the south-west, swinging round a sharp elbow, it looks as though it were a big side-glen from the right which causes it to change its direction; but there exists no such side-glen. At the point in question the valley is joined by only three small gullies or steep fissures, which start on the summit of the nearest mountains and form at their lower end vast screes of accumulated gravel. In unison with the phenomenon which Richthofen calls »diagonale Stromverschiebung», the river cleaves a passage to the left,
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