550 OROGRAPHY OF CENTRAL TIBET.
character, though two of them are main passes, with altitudes of 3797 and 4079 m. respectively, belonging to the westward prolongations of the Akato system.
In the source-regions of the Kara-muran I had again to cross over two main passes in order to reach that part of the North Tibetan plateau which is situated north of the Arka-tagh. These were the Dalai-kurghan-art (4357 m.), situated in the range that corresponds to the Lower Astin-tagh, and the Japkaklik-davan (4741 m.), in the range that corresponds to the Upper Astin-tagh. Thus here again the border montanic system is double, just as it is all the way westwards to Pamir.
The part of the middle Tschertschen-darja which flows towards the west and is bounded on the south by the Tokus-davan and the Musluk-tagh and on the north by the western portion of the Astin-tagh proper, flows unquestionably through a true latitudinal valley, of equivalent rank with the Tschimen valley and the great latitudinal valleys up on the Tibetan plateau, although it is essentially differentiated from them by its terminating in the lowland basin of the Tarim. Nevertheless it is difficult to make out how the Astin-tagh ends over against this valley. Possibly one of the twin ranges may be pierced by the latter; and support is lent to this supposition by the circumstance, that the travellers who have crossed over the extreme western tip of the Astin-tagh proper, in the elbow of the Tschertschen-darja itself, speak only of one pass, namely the Tschoka-davan, which according to Pjevtsoff reaches an altitude of 2906 m. De Rhins too crossed over this pass, but he gives it no altitude, any more than Littledale does, though the latter calls it the Chokur Pass. Indeed on Littledale's map we find the altitudes of his camps only, but more rarely the altitudes of the passes, though these are of course much more important. Nevertheless the existence of only one pass along this route seems to suggest that one of the two Astin-tagh ranges has terminated, or perhaps more correctly has been broken through, before it reaches the latitudinal valley of the Tschertschen-darja.
Advancing yet another stage towards the east, we come to regions that are comparatively well known, and there I move with a feeling of far greater certainty, because I have crossed them in several places. These regions will also show very distinctly on my general map of Tibet (scale i : i ,000,000); and of the general structure and configuration of this portion of the country at all events it will be possible to obtain a clear idea. I had indeed intended entering here more into detail, as I have in fact pledged myself to do in the preceding pages; but such detailed recapitulation appears to be in the meantime superfluous, and not least so for the reason that the study of my geological material is not yet completed. In the meantime I will therefore content myself with a brief general statement.
We have ascertained, then, that that part of the Astin-tagh which lies south from the Kara-koschun is a double range and farther east splits up into several chains, running in sharply accentuated parallel directions. Immediately east of the Dschahan-saj there is a mountain-road, which has been used by several travellers, and which crosses over the twin ranges in the passes of Kum-davan and Taschdavan respectively, the former having according to Carey an altitude of 3262 m. and the latter of 3963 m. This route was also used by Bonvalot; but that traveller gives no altitude for the Kum-davan, though he puts the Tasch-davan at 5200. According to Pjevtsoff the last mentioned pass only reaches 3808 m. I my-
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