The surveys represented in. this sheet,
which comprises the ancient territory of Lou-lan in the western portion of the Lop
desert and the Kuruk-tagh ranges to the
north of it, date mostly from the third expedition. The work of 1906-08 is con-
fined to the desert routes followed from the
Tarim to the ruins of the Lou-lan Site (D. 3) and back, and to that leading from TTurfân to Singer (B. 2) and thence to Korla. The exploration of all ancient remains traceable in the Lou-lan area, once passed by the Chinese high road from Tun-huang to the
Tarim basin, formed an important task both
.on the second and third expeditions. This accounts for the comparatively close network of traverses covering what is now all water-
less desert of wind-eroded clay, salt and drift-sand, in the south-eastern quarter of the sheet.
In the course of compilation all plane-table work was adjusted on the positions
which had been adopted for Altmish-bulak,
Korla and intermediate points on the basis of an erroneous adjustment of R. B. Lal
Singh's triangulation. This error arose
through acceptance of the very distant connection between the northern and south-
ern sections of the triangulation, which rays observed from the Astin-bulak stations (D. 3) to Pk. 1/75 E (Peak 13,170, in Sheet No. 30. D. 2) were assumed to furnish. The reasons, which on re-examination in 1921 indicated faulty identification of this junction point and caused this distant 'connection to be rejected, are fully explained in Major Mason's notes in Appendix A (Groups H
and I, pai=a. 2). The position of Altmishbulak Camp Station, as previously adopted
and shown in the map, is lat. 40°56'27",
long. 89°52' 36"; the coordinates of the same, as determined on the basis of Mr. Clementi's
values of Korla, are lat. 40° 53' 29", long. 90° 19' 55" (see Appendix A, Sheet N. K
14 As explained in Major Mason's note (Appendix A, Group I, .pare. 4), the heights shown in the map for triangulated points from Astin-bulak to Korla were derived from the faulty connection above mentioned. They require an addition of about 237
46n). It deserves to be noted that Dr. Hedin's map assigns to Altmish-bulak the values of lat. 40° 57' 16", long. 89° 59' 24".
The position of Altmish-bulak as adopt ed in the map has resulted also in a shift to the west of that assigned to the Lou-lan Site (Camp 83, 124, at L.A. Stùpa ruin; D.3). This junction of numerous routes is now placed with long. 89° 46' 20" against 89° 52' 40" in Sheet No. 60 of the 1906-08 map and Dr. Hedin's longitude 89°50'53" for the same point. The same may be noted also in the location of Singer (B.2), another important route junction, which is now shown with long. 88°38' 10" against 88°47' 40" of the 1906-08 map.
In addition to the latitude values recorded below, use was made of one observed by Dr. Hedin on the Tarim river (A.4).
The area comprised in this sheet, all desert and almost wholly waterless throughout, falls into two regions quite distinct in physical charcter. In the northern portion we have the utterly barren and much-decayed hill-ranges of the Kuruk-tagh. They are divided by wide plateaus descending for the most part into drainageless basins, salt-encrusted and dry except after rare floods. The highest of these ranges is the one which, striking approximately from east to west, passes close to Singer. To the west of this,
the only permanently inhabited place in the Kuruk-tagh with a small patch of cultiva-
tion, the range culminates in the rugged Hsi-ta-shan (A.2), probably the greatest elevation of the whole Kuruk-tagh. 14 To the east of Singer the rare springs found are all salt. What scanty vegetation exists is confined to the vicinity of springs and to some of the depressions.
From the gravel glacis at the foot of the Kuruk-tàgh, there extends southwards an
utterly waterless desert, over-run by drift-sand and, wherever bare of dunes, undergoing
feet, as now shown in the tables for International Sheets N. K.455 K, o, s, w, X, to bring them into accord with the height of the Astin-bulak base (2,830 feet), derived from mercurial barometer readings.