292 THE BASIN OF EASTERN PERSIA AND SISTAN. 
While there is no direct evidence as to the time of the uplift, it seems safe to 
associate its inception with the first accumulation of g^ravel around the lake of Sistan. 
Judging from the appearance of the lava cap of the mesa, it must be of approximately 
the same age as Kuh-i-Chaku. 
How long the process of uplifting the mountains continued or how widely 
it extended we do not know. The distorted shorelines which I shall presently 
describe show that warping continued till very recent times. To-day earthquakes 
seem to be unknown in Sistan, but Mr. Tate informed me that either Iben-i-Haukl 
or Iben-i-Batuta record the occurrence of one in the eleventh century. On the edges 
of the vSistan basin, however, earthquakes still persist. Two hundred miles to the 
south the smouldering volcano of Kiih-i-Taftan proves that the forces of vulcanism 
are still active ; while 300 miles to the eastward McMahon (a, p. 10) reports that 
earthquakes are common along a remarkable fault-crack which extends north and 
.south for 120 miles along the Afghan frontier between Kandahar and Quetta. It 
is highl)' probable that the basin of Sistan, like so many of the other basins of 
Persia, is being uplifted along the edges. The invasion of gravel in a thin sheet on 
everj' portion of the basin floor may be due in part to these mo\-ements. 
A detailed study of the thick gravels near Kuh-i-Chaku is difficult because of 
the extent to which the deposits are hidden by their own talus. Sections E and F, 
however, show that the gravels are interstratified with finer beds of silt, red for the 
most part. The alternating beds seem to be related in the same manner as the 
alternating clays below ; the gravels seem to occupy a place corresponding to the 
pink clays, while the silts correspond to the green lacustrine clays. The problem 
of accounting for the alternations in the upper strata is the same as in the clays, and 
the same reasoning applies. If our conclusions are correct, earth-movements, of which 
the \olcanoes were one manifestation, elevated the northwestern corner of Sistan, 
reviving erosion among the mountains and raising part of the bottom of the lake 
beyond the reach of the water. The clays of the lake bottom were exposed to erosion 
and certain layers were carried away, forming an unconformity, but soon abundant 
gravel was brought down from the renewed mountains and the whole country was 
buried in it. This must have happened during an interfluvial epoch, as appears 
from tlie gravels. A fluvial epoch then ensued, and, to use a word not recognized 
by lexicographers, the ungradation of the mountains was checked. The conditions 
of the fluvial epoch favored the preser\'ation of the graded slopes of the mature 
topography of the uplifted mountains, and the stripping which had progressed 
rapidly during the interfluvial epoch was retarded. Accordingly the materials 
brought down by the streams were fine-grained, and silts accumulated upon the 
gravels. Thus it seems probable the changes went on until three more were added 
to the ten fluvial epochs that had gone before. The evidence for these last three is 
not so abundant or conclusive as for their predecessors ; but three strong strata of 
gravel separated by finer material cap the bluffs in many places where no sections 
were obtained, and it is difl[icult to explain them otherwise. We rebel at the 
thought of adding epoch to epoch in such wholesale fashion, yet thirteen or a 
hundred epochs of climatic change are as reasonable as two. 
