72 EXPLORATIONS IN TURKESTAN. 
and flocks, is an immediate response to the distribution of vegetation, as thus 
determined. 
The prevailing absence of trees is tlie most notable feature of the vegetation. 
There were open groves of poplars close b)- some of the streams, Ijut where the 
more important trails followed the valleys the trees had been unmercifully trimmed 
or felled for firewood, and few remained standing. In one of the branch valleys of 
the Alabuga a single large tree ser\'es as so notable a landmark that it is entered 
upon the large-scale Ru.ssian map. On our way from the Narin Valley up to Son 
Kid, we passed through fine groves of coniferous trees, but their occurrence was 
exceptional. Nothing of the sort was seen at similar altitudes when descending 
from Son Kul into the Tuluk Valley. Again, during our ascent into one of the 
south-opening vallej'S of the Kungei Ala-tau, north of Issik Kul, fine groves of 
conifers occupied the more shaded slopes of the side ravines. The line between 
trees and herbage was often verj- sharply defined. This was noted by Severtzof, who 
ascribed the general absence of trees to a recent change from a moister to a drier 
climate (1875, 66, 67); but it is difficult to believe that the prevailing absence of 
trees is natural on mountain slopes where flourishing groves are occasionally found. 
It seems more reasonable to ascribe the treelessness of the mountain sides to their 
long occupation by nomadic pastoral tribes, to whom pastures were of greater value 
than forests. It would be interesting, in this connection, to inclose and protect 
certain of the mountain tracts from grazing, and to plant them with tree seeds or 
young trees ; and it would be surprising if a thrifty growth did not result. It is also 
noteworthy that the absence of trees is not accompanied either by small rainfall or 
by barrenness on the mountain sides. Rains were abundant in the higher ranges 
in Juh', and gra.ssy herbage grew there luxuriant!)'. 
An interesting contrast in the relation of vegetation to insolation was noted 
in passing from the deeper valleys to the higher mountains. In the bad-lands of the 
Narin basin, at altitudes of 6,500 or 7,000 feet, the sunny slopes were prevailingly 
bare and minuteh' dissected, while the shady slopes were occupied by a sparse 
herbage and were of smoother form. On the high spurs of the Kungei Ala-tau, at 
altitudes of 10,000 feet or more, and above the tree line, the sunny slopes had the 
better cover of grass, while the shady slopes were relatively barren. In the first 
case, sunshine promotes aridity and exchides vegetation. In the second case, 
sunshine promotes snow-melting and favors vegetation. 
DEVELOPMENT OF THE TIAN SHAN MOUNTAINS. 
A number of the mountain ranges that we saw were of vigorous form, with 
sharp peaks and deei>car\'ed ^•alle}•s, in which it was impossible to recognize any 
trace of the original unsculptured mass ; but certain observations made in the central 
and northern ranges, near Lakes Son Kul and Issik Kul, and on the steppes that 
border the mountains on the north, led to the belief that the region had been verj' 
generally worn down to moderate or small relief since the time of greater defonna- 
tion, which probably occurred in the Mesozoic age ; that large areas of subdued or 
extinguished mountain structures are still to be seen in the low ranges and in the 
