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Search for continua-
tion of
Limes.

The search made there and farther south on that day failed to reveal any sign of the continua-
tion of the Limes wall, such as is likely to have existed on the right bank of the river opposite
T. XLVIII. b, its last traced point. The line of the Han wall might possibly have made a big bend
so as to protect the northern end of the oasis, but there was no time for a prolonged investigation
of the ground higher up the river as a halt was objected to by the Mongol guides and owners of
our transport. The look-out we kept on our marches farther south also failed to reveal any indica-
tions of the Limes on the barren hills and plateaus that we passed. Thus the task of tracing its
continuation to the east of the Etsin-gol had to be left to some future explorer. Considering the
nature of the ground to be searched, he will need all the help that a cool season and adequate camel
transport can offer.

Desert
hills crossed
to Kao-t'ai.

Another five marches, covering a total of over a hundred miles, brought us by Midsummer
Day to the town of Kao-t'ai by the Kan-chou river. Of the route followed, hitherto unsurveyed,
there is little for the non-geologist traveller to record, apart from the topographical details shown
in Maps Nos. 42. D. 4; 45. A. 4; 46. A. 1, 2. It took us over four gradually rising hill ranges;
the ascent of the first was over a bare glacis of gravel, and the next three were separated from each
other by wide valleys where scattered patches of hardy scrub and tamarisk growth offered grazing
for camels. Except in the southernmost range crossed between Camps 162 and 163, the rocks
which compose these hill-chains rarely emerge from the masses of detritus that smother their sides
(Fig. 259). Until the traveller reaches the northern slope of the range just mentioned, over-
looking the Kan-chou river, water is to be found only in the single well of Ta-shan-kou (Map No.
45. A. 4) and the two scanty and distinctly brackish springs of Yüeh-kung-ch'üan and Zigda-kaya
(Maps Nos. 42. D. 4; 46. A. 1). A few stunted Eleagnus (Jigda), clinging to the cliffs of granite
which flank the latter spring (Fig. 260), were the only trees met with.

Descent to
Kan-chou
river.

It was clear that these wastes of decomposed rock, sand and gravel can receive but the scantiest
rain or snow-fall. Such atmospheric moisture as may pass northward from the Nan-shan is probably
almost all caught and precipitated on the higher ranges to the south, known to the Mongols as
Kôka-ula, which clearly shows the effects of water erosion on its barren slopes. This range, as
Map No. 46 shows, is undoubtedly a continuation of the high and rugged chain that overlooks
Kan-chou from the north and is itself a portion of the Ala-shan system. Whatever change this
ground may have experienced through 'desiccation' during historical times, it is certain that the
route leading across it could never have served, like that along the Etsin-gol, for the advance of
a large invading host. But raids by small parties of nomads were easy enough here, and it was to
give warning of these that the watch-towers were set up which we found crowning the last rocky
knolls before passing through the crumbling line of the mediaeval 'Great Wall'. Immediately
beyond we were greeted by the smiling green fields of the village of Lo-pa, which stretch down to
the right bank of the Kan-chou river (Map No. 43. D. 2). It flowed at the time in a single deep
channel about 80 yards wide, which we crossed by a ferry-boat; and after a mile's ride I found
myself back at the eastern gate of the lively little town of Kao-t'ai, which I well remembered visiting
in September, 1907.

Halt at
Kao-t'ai.

In view of the fatigues undergone by men and beasts on the long hot journey, I was here
obliged to make a two days' halt in the cool shady quarters which were once again hospitably
offered me in a large temple outside the town gate (Fig. 264). My time was occupied in arranging
for cart transport by which I might reach Kan-chou quickly by the high road, and also in a brief
survey reconnaissance to the south. I ascertained from this that the barren foot of an outlying
spur of the Richthofen range approaches here within five miles of the Kan-chou river, thus greatly
reducing the width of the cultivable portion of the 'thalweg' that forms the great natural highway