ORGANIC PROCESSES IN UNDRAINED ASIA. ie) 
toward the present condition of aridity—a trend that was interrupted by oscilla- 
tions, in some of which the aridity may have exceeded that of to-day—a process 
in which the seas, while responding to the oscillations, have in the main shrunken 
gradually to the volumes compatible with the present equilibrium between pre- 
cipitation and evaporation. Parallel with this progress toward aridity, under 
the diminished precipitation and lessening to disappearance of the ameliorating 
climatic reaction of the once-expanded water areas, was the shrinkage of the loess 
zones. ‘The grassy steppes, which had once teemed with life and permitted the 
distribution of ruminants and the horse across all Asia to Europe, gradually became 
broken up into disconnected areas by the increased intensity of desert conditions. 
The expanding deserts cut off the connection between the faune of southern Tur- 
kestan and Persia on the one hand and those of Europe on the other, and allowed 
the evolution of regional varieties. And there must have been a similar reaction 
upon the distribution of man. 


Fig. 2.—Beginning Work at the North Kurgan. 
After this, a continued progress towards extreme aridity advanced the desert 
sea of sands till its dune-waves, rolling ever nearer to the mountain, completely 
submerged long stretches of the narrowed loess-zone between the now restricted 
deltas at the mouths of mountain streams. The teeming herds of ruminants and 
horses disappeared over vast areas, and life was restricted to the mountains and to 
the borders of the few remaining streams and the deltas. 
When this stage had been reached, in early prehistoric time, and long before 
the introduction of irrigation, the condition of southern Turkestan and northern 
Persia may be summed up as one of deserts, relieved only by oases in high valleys 
and on the deltas at the mouths of streams emerging from the mountains, or where 
larger rivers died out on the plains or entered the shrunken seas. The delta-oases 
have been the home of man from early prehistoric time till now, throughout 
Turkestan and northern Persia. On one of these, at Anau near Askhabad, 300 
miles east of the Caspian, we made, in 1904, excavations and physiographic 
studies. 
