DESERTS. 289 
that low relief was dissected during the following three uplifts with their erosion 
cycles. It is gratifying to find corroboration of this threefold division of uplift 
in the structural deformations of plain-deposits derived therefrom. ‘There are 
three rows of uptilted piedmonts ranging parallel to the Alai Mountains, as the 
three respective marginal deformations corresponding to the threefold uplift 
both in magnitude and degree of subsequent erosion. It is further interesting 
to find that these three belts of uplifted piedmont, which converge towards the 
mountains opposite Khokand, near the western or lower end of the basin, widen 
eastward to include a considerable area of the eastern end of the plains, where 
deposition has necessarily been much heavier, as that portion lies before a vast 
mass of high-uplifted mountains. Another feature affected by this process and 
characteristic of the Fergana plains, especially on their Alai side, is the threefold, 
and sometimes fourfold, division of distributary systems. Larger streams descend- 
ing from the Alai cross all three belts of uptilted piedmont, having cut down as 
they were uplifted, and apportion their depositions over areas between them, 
some escaping beyond the last to spread towards the middle of the basin. Each 
stream, therefore, gives rise to from two to four successive groups of delta-oases, 
thus giving an interesting variation of type Ia of my classification. In several 
instances a stream escapes from its first delta in two or more distributaries to 
form other deltas beyond, so that the intervening uplifted ridge of piedmont has 
been dissected by two or more channels separated by many miles (fig. 465). 
The oldest belt of uptilted piedmonts bordering the Alai Mountains probably 
contains products of the first erosion cycle and was thus upheaved during the 
uplift which caused the breaking up of its peneplain stage. On the Terek trail 
between Osh and Gulcha it attains a height of over 3,000 feet above the present 
Gulcha River flood-plain. There it is a mass of loosely cemented conglomerates 
with confused dips, and of which the old surmounting piedmont topography has 
nearly disappeared. The later upheavals of plain-deposits rarely rise more than 
a few hundred feet above present deposition. 
Where we approached the northern margin of the Fergana plains in the regions 
of Chust and Khojent, only one belt of uptilted piedmont was observed, probably 
because the mountains on that side are much lower and doubtless have been so 
in the past. This one belt, however, is of especial interest as it can be traced 
all the way from Namangan to Khojent, a distance of about 140 miles, and crosses 
the Syr Darya, which has cut down as it was uplifted. 
From the standpoint of hydrography alone, the Fergana basin expresses 
the same series of cyclical events deduced from the topography and structure 
of its mountains and plains. In the mountains larger streams join at oblique 
angles and generally inherit the courses held before the first uplift of the low 
relief then drained by them. Their smaller tributaries contrast with this rule 
by joining the larger nearly at right angles and have come to be since that uplift, 
We have seen how streams descending from the Alai split into distributary systems 
in a manner determined by the marginal deformations of the plains and that 
feature may be recognized with a glance at the hydrography on a large-scale 
Russian map. 
