LOESS IN FERGANA. 6 1 
There is, however, another condition that is even more adverse to the suppl)- 
of wind-borne silts. This is found where the streams have incised their courses in 
narrow gorges instead of broadly spreading their floods over torrential fans; that 
is, where the streams are engaged in degrading instead of aggrading their beds. We 
crossed a degrading stream about 7 miles west of Khojent. It had for some 
reason cut a sharp and deep trench in the plain, so that it was not seen until we 
were close upon it. There was no possibility of its overflowing the plain, and so all 
its silt was washed along its channel. The sprawling and shifting streams else- 
where seen on the fans were in most marked contrast to this secretive river. Hence, 
in so far as loess is derived from rivers, there can be little question that it comes 
from aggrading rather than from degrading streams ; and this conclusion seems to 
be applicable to the loess of the Alpine region, as described by Penck, and to that 
of the Mississippi basin, as described by Shimek and others, as well as to that of 
Turkestan. 
The ride through Fergana was most entertaining from its variety. The great 
snowy ranges of the Alai rose in the south. Their Alpine crests and snow fields 
were brilliantly clear in the early morning. By noon they were much hidden under 
diurnal cumulus clouds. We could see, with our field glasses, man)- features of gla- 
cial origin, further described below. Northeast of Khojent was an e.xcelleut exam- 
ple of one of those sharply dissected ranges at whose base a series of digitate spurs 
interlock with branching valley floors, so as to make a most sinuous base line, in 
strong contrast to mountain ranges of simple border, like the range south of Jizak. 
The latter seems to belong to the class of somewhat dissected fault blocks; the 
former, if it ever had a faulted front, has lost all signs of it. South of Maxrani rose 
a high dissected dome of apparently crystalline core, wrapped around by colored 
sedimentaries — first, a dark belt that lapped on the flanks of the dome, then a weak 
gray belt; then more resistant red beds. The colored belts are nmch narrowed 
as they curve around the northern base of the dome from east and west, as if they 
were torn by marginal faulting or tilted to steep dips. Dissected fans stand forth 
from the larger ravines of the dome; younger and smoother fans are built at 
their base ; then come the gravelly flood plains of the streams, with many dunes 
heaped on them. Near Marghilan we passed benches of uplifted gra\-els, probably 
corresponding to the uplifted and dissected sub-recent ridges that we saw a few 
days later on a ride south of Andizhan. Here the strata dipped 10° or 15° north- 
ward, and fine gray silts alternated with coarse gravels. Similar alternations of 
gravels and loess-like silts were seen in the borders of the Kugart \'alle>', where we 
entered the Tian Shan ranges on June 30. 
LOESS IN SEMIRVETSHEKSK. 
Much loess was seen on the steppe west of Vyernyi at the northern base of 
the Trans-Ili Ala-tau ; it seemed less dissected than the deposits west of Samar- 
kand and south of Tashkent. More remarkable deposits of loess were seen while 
posting across Semiryetshensk — the Seven-river district — from \'yemyi northward 
