CHRONOLOGY—CYCLES OF CLIMATE AND CHANGES OF CULTURE. 59 
ment on the South Kurgan and the city of Anau were both founded during the 
last aggrading. The arid period between the two last aggradings coincides with 
the long abandonment of the South Kurgan between the copper and iron cultures, 
and the previous arid period coincides with the interval between the North and 
south Kurgans. Lastly, in addition to the agreement shown in the rise and 
decline of civilizations, we have confirmation from the biological side in the pro- 
gressive stunting of the breeds of domesticated animals, as shown by Dr. Duerst, 
which, according to him and to Nehring, is due to insufficient food and to desert 
conditions. 
We have no direct observations as to whether the valleys are now deepening 
on the zone of tilting in the present period of aridity, because under irrigation 
the silts are all held up, and alluviation is artificially maintained up to the apex 
of the deltas. 
It would be of great interest to know whether these cycles were of proximately 
equal periodicity. Unfortunately, the two critical factors in the problem, depth 
and rate of valley-cutting, are wanting. Penck has shown that the last of his 
four ice-epochs of the glacial period was followed by a series of lesser though 
great oscillations of diminishing intensity; and it is thought that the oncoming 
and passing of each glacial epoch was marked by climatic oscillations of respec- 
tively increasing and decreasing intensity. Our cycles at Anau covered periods 
of between 3,000 and 4,000 years’ duration. Oscillations of such magnitude would 
seem to belong in the order of phenomena of mundane extent and possibly of 
astronomic relations. The question may be risked, I think, whether they may 
not be fainter vibrations in a series, diminishing in intensity since the last of 
Penck’s oscillations. 
The argument contained in this chapter, and represented graphically on 
plate 5, is based on observed facts and on the writer’s inferences drawn from these 
facts. As facts of observation, we have in three neighboring sites an aggregate 
of 170 feet of culture-strata of uniform character belonging to the distinctly differ- 
ent cultures of five separate and successive occupations. That part of the argument 
which establishes the parallelism between the physical and human history of the 
region, rests upon observed parts of three periods of aggrading with two inter- 
vening periods of cutting-down of the valley. The aggradings are drawn in full 
lines in each case opposite that part of the culture-strata during the accumulations 
of which the aggrading took place. These full lines represent, therefore, the 
minimum depth of valley deepening, the observed amount and maximum height 
attained by aggrading, and its duration measured in feet of contemporaneously 
accumulating culture-strata. It will be observed that the essentials of this part 
of the argument consist in the observed aggradings, represented by full lines, and 
length of cycles. Plate 5 tells us the history of the oasis of Anau free from the 
writer’s inferences, but it is desirable that some things previously stated be 
repeated at this point. 
