EXAMPLES OF TERRACES. 265 
chief ungraded streams of several neighboring mountain ridges. Yet such must 
necessarily be the case, if the gravels and their terracing are due to a tectonic cause. 
The most probable explanation is that they occur in valleys which are ordinarily 
ungraded and hence subject to erosion, but which became graded during one of the 
fluvial epochs, perhaps not the latest, when the climate was so altered that even 
these valleys assumed a graded condition and were floored with flood-plains of gravel. 
The Nemeksar, or playa of Khaf, is a broad, almost waterlesss expanse of salt, 
much like the Pul-i-Khatun salt lake. In the late winter it is said to be entirely 
covered with water, although in mid-December we saw but a few detached bits of 
open water and were able to ride out nearly a mile before the nmd became dis- 
agreeably deep. On the northern edge of the playa, where high mountains rise 
within a few miles, huge fans of coarse, angular gravel temiinate close to the edge 
of the playa floor. Where they approach this most nearly they end in a distinct 
bluff", which is from 6 to 10 feet high and has its base 10 or 12 feet above the edge 
of the area that seems now to be subject to inundation. Between this latter limit 
and the foot of the little bluff" there is either no gravel or else a little very fine grit 
that has been brought in recently. The greater part of the fonnation here is a very 
fine silt, crusted thickly with salt. Where the fans do not extend as far as the line 
at the base of the bluff's, they die out gradually and irregularh- on a deposit of silt 
of the kind just described. In their upper courses these fans are dissected by chan- 
nels which at first grow deeper until they reach a maximum of 12 or 15 feet near 
the middle of the fans, and then decrease toward the playa. They appear to be 
channels cut during a fluvial epoch through a zone of maximum deposition fonned 
at a previous time of greater desiccation. The phenomena along the edge of the 
playa seem to indicate a somewhat higher stand of the water at no ven,- distant 
day. The high-water level of the present is indicated by an ill-defined beach a 
few feet below the base of the little bluflfs. Along the east side of the playa, as to 
the north, the main tributary valleys show two strong terraces which sometimes 
reach a combined height of 100 feet. They are of the usual t\pe, deeply covered 
with gravel. Where the formations surrounding the lake consist of soft Tertiary 
fonnations, there is some indication of ancient undercutting by the waves at higher 
levels. This feature is much better shown in the playa of Kulberenj, which lies in 
the Khaf basin a little to the south of the main playa. 
KDLBERENJ. 
At Kulberenj the whole playa is surrounded by two strong lacustrine terraces, 
one of which rises from 20 to 25 feet above the pla^a floor, and the other over 50. 
Below these there is in places a faint third terrace which would be too indefinite to 
mention if it were not that in other places similar traces of a last faint terrace-making 
epoch are evident. The two larger terraces consist of fine silt, on which is a cover 
of gravel 4 or 5 feet thick. Whether or not the silts are the deposits of an ancient 
lake of great size is not certain, although it is probable. The cutting of tlie terraces 
is clearly the work of three diff"ereut lakes, or of one lake working at three diff"erent 
levels. Naturally the tributary valleys are terraced to correspond to the lake. The 
phenomena of Kulberenj, Khaf, Pul-i-Khatun, and Shor Kul in Chinese Turkestan 
(see the report on Turkestan), all agree in showing that two or three times in 
