258 THE BASIN OF EASTERN PERSIA AND SISTAN. 
diverts a part of the river. According to Mr. Nikrashevich, superintendent of the 
dam, the inner terrace at the bottom of the old channel had a height of 2 feet before 
conditions were changed by the building of the dam, while the inner channel, where 
the stream to-day runs, has a depth of about 16 feet. That is, the bottom of the 
river to-day is 14 feet lower than it was at the time of the abandonment of the old 
channel a hundred years ago. Part of this difference, however, may be accounted 
for by filling of the latter subsequent to its abandonment. 
Since the building of the dam the river has so filled up its channel above the 
artificial obstruction that the lower terrace has entirely disappeared and the stream 
has no proper channel, but wanders this way and that over its own depo.sits. This 
wandering is causing the widening of the flood-plain, and there is great danger that 
in time a sudden change in the course of the main stream will cause it to cut into 
the banks close to the dam and finally to break a way around the end of the latter. 
Such a catastrophe took place at Sultan Bend, a few miles up the river, where a dam 
was built about 1890 and was abandoned a few years later. Retaining walls were 
built in all directions, but nothing could prevent the river from cutting laterally 
when it was prevented from accomplishing its normal work of vertical erosion. 
The material which is now being deposited by the Murg-ab seems to be the 
same as that which is exposed in the bluffs of the terraces. It consists of a very- 
fine clayey sand well stratified and with a consistency like loess. It stands for years 
in nearly perpendicular bluffs, and preserves the marks of the pick indefinitely. It 
is said that as far as Tash Kupri, nearly a hundred miles upstream, the same fine 
sandy deposit continues, and only at that place does it become gravelly. 
The terraces also continue far upstream. At Tash Kupri there are said to be 
two, one of them close to the river and the other 70 feet above it. At Sultan Bend, 
15 miles above the dam at Hindu Kush, there are three terraces. At the top lies 
the great sand-covered alluvial plain, 70 feet above the river ; then comes a broad 
terrace co\'ered with tamarisk and other bushes, and hing about half as high ; and 
lastly there is a small young terrace only 10 feet above the water. Here, again, as 
in so many other cases, there is no positive indication as to whether the terracing 
is due to climatic or tectonic causes. There are archeological indications that the 
flow of the Murg-ab one or two thousand years ago was more abundant than at 
present, and it is not impossible that the decrease in the size of the stream is con- 
nected with the building of the lower terraces. 
THE HERI ROD. 
The Heri Rud, or Tejen River, as it is called after it enters Russian territory, 
when taken by itself is no more conclusive as to the cause of the terraces than are 
the other rivers. To be sure, it flows directly across the northern mountain rim 
of the basin of Iran, and thereby differs from the other streams which we have 
considered. If the terraces are due to an extensive uplift of Kopet Dagh and the 
Paropamisus, the main axis of that uplift must have passed directly athwart the 
Heri Rud not far from what is now the Afghan border, accelerating the lower or 
northern portion of the stream and retarding the upper portion. The process of 
terrace-making under such circumstances would differ materially from that in cases 
