330 PHYSIOGRAPHY OF CENTRAL-ASIAN DESERTS AND OASES. 
A second reexcavation of the valley was followed by its third-epoch growth 
filling the last channel, and this growth was in process when Anau city was founded 
and the stream was probably wholly used for irrigation, and so the growth has 
continued till now in the form of irrigation sediments, raising the delta plain 
around our kurgans to a height of 20 feet above its ancient first-epoch surface on 
which the two kurgan oases were founded. In it there is more sand than in any 
of the preceding epochs and it is likewise more rapid in appearance. 
SUMMARY OF THE MORE IMPORTANT FACTS OF THE PAST PHYSIOGRAPHY OF ANAU. 
First cycle. 
Pliocene, Kopet Dagh worn to low relief. 
Immense deltas built. 
Second and third cycles (Quaternary). 
Two uplifts of Kopet Dagh and corresponding general sinking of plains, while the 
piedmont deltas of the first cycle are bent up along the base of the mountains. 
Valleys excavated and prolonged through old uptilted deltas to build new, smaller 
ones beyond. 
Fourth cycle (Postglacial). 
Mountains continue rising again and the new delta at Anau continues tilting, but so 
slowly that with sufficient alluviation it grows. 
Reaction to dry and formation of delta valley. 
Reaction to wet and alluviation of delta valley. North Kurgan founded. 
During oscillations in precipitation over the mountains, alluviation twice again falls 
below rate of tilt and our buried delta valley thus twice again comes to be. 
Precipitation now scarcely in excess of underground drainage. 
Dunes desiccated of grass and set free to encroach on the delta plains. 
OASES OF THE MURG-AB DELTA. 
THE RIVER MURG-AB AND THE TYPE-PECULIARITIES OF THE MERV OASES, 
PAST AND PRESENT. 
Rising in the mountains of Afghanistan and swollen by their melting snow 
and ice, the River Murg-ab issues north onto the plains of Transcaspia. There 
it splits over a large subaerial delta 100 miles from the mountains and inclosed 
by dunes of sand wind-sifted from its river silt. This far-expanded sea of drifting 
barkhans merges into the desert of Kara Kum, making the great delta a seat of 
oases extreme in desert isolation. At one time the Murg-ab may have joined the 
Oxus, and in still more remote antiquity may have flowed direct into an Aralo- 
Caspian Sea. Its chief oases may, therefore, in the past have changed through 
type V, type II, and finally into type Ia; from lake shore to river bank, and at last 
the oases of an isolated delta. From the time when it failed to join either Oxus 
or Tedjend or reach a sea, the Murg-ab flowed to build an independent delta, and 
its oases were delta-oases, which, in the course of centuries, moved with the delta 
out and back, or perhaps always back if the river shortened with continuous 
desiccation. Here and there upon the clay surface, and beyond the limits now 
attained by water or even where the sand is drifting in, are seen mounds of clay 
and crumbled walls, the ruins of ancient towns and cities. 
