g6 EXPLORATIOXS IN TURKESTAN. 
RIVERS OF THE ISSIK KUL DISTRICT. 
The rivers in the Issik Kul district proclaim their association with new-made 
ranges by their habit of (until recenth) aggrading the longitudinal valleys and 
of eroding the transverse valleys. This is notably the case in the members of 
the Chu system. The lower Tuluk Valley contains in its longitudinal portion 
several hundred feet of yellowish clays, interstratified with lenses and layers of 
coarse gTa\els and cobbles, all now dissected. The stream turns abruptly north- 
ward from this aggraded and dissected trough to a deep and narrow gorge through 
the eastern extension of the Chalai range, and then joins the Juvan-arik. The 
gorge is passable at low water, but at the time of our \isit the Tuluk-su was too 
high to pennit us to follow it, and we had to make a detour over a low pass. The 
upper (western) part of the Tuluk \'alley, where we first came to it north of Son 
Kul, did not present any sure signs of being a valle}- of recent deformation ; its 
sides were well dissected ; its lower spurs were well graded ; its present flood plain 
was eroded 50 feet or more below an earlier valley floor ; yet all this is consistent 
with the origin of the valley by subrecent defonnation, followed by dissection of 
its sides, accumulation in its most depressed part, and erosion of its transverse 
^ALEXANDER RANGE 
Kachkar Basin 
KOK-TAL RANGE 
Fig. 62. — Fifteen-mile section across the Kach-kar Basin, looking east. 
outlet. The change toward a more arid low-level climate, indicated by an increas- 
ing sparseness of vegetation as we rode down the \alle)-, was distinctly noticeable 
in a distance of 10 or 15 miles. 
The Ju\an-arik comes from the east in a longitudinal valle)' on the south side 
of the Terskei Ala-tau ; then turns northward near the junction with the Tuluk-su 
and follows a deep gorge (fig. 43) — one of the wildest gorges in the Tian Shan, accord- 
ing to Severtzof (1875, 73) — through the range, here called the Yukok-tau (Son Kul 
Gebirge on Friedrichsen's map), to the Kach-kar basin. The longitudinal valley 
contains clay deposits of a yellowish or reddish color, but these are now so deeply 
dissected as to expose the rock floor on which they rest. Since the deep dissection 
there has been an accumulation of gravels and cobbles, capped with gra)- silts, but 
these deposits are also trenched, and the present river flows in an open flood plain 
below the terrace remnants of the gravels. The traus\-erse gorge has steep, ragged 
walls of granite, basalt, and diorite, between which the ri\-er rushes on a rapidly 
descending bowlder bed. There are few signs of terracing in the gorge, but where 
lateral ravines open in the walls, benches of gravel remain. 
The Juvan-arik joins the Kach-kar in a longitudinal basin of the same name, 
and their united waters flow eastward and northward toward Issik Kul, under the 
name of Urta-takoe. The Kach-kar basin has already been referred to as an 
aggraded area of depression correlated with the uplifted and dissected block of the 
