THE TERRACES OF SISTAN. 3OI 
no lack of other activities. Earth-movenienLs have taken place, mountains have 
been nplifted, plateaus have been carved into mountain ridges, basins have been 
intensified, and volcanoes have poured forth sheets of lava, but all these actions 
have been more or less local in their application. On the whole, their action in 
Eastern Persia during Tertiary and Quaternary times has tended steadily in the 
one direction of elevating the mountains and increasing their area, while at the 
same time the basins have grown steadily smaller by the folding up of their edges. 
Nevertheless, this action has not gone on simultaneously over the whole country, 
and there are many parts of Persia where as yet we have found no evidence of 
tectonic action since the end of the Tertiary era. 
With climatic changes the case is different. Their action is uniform over broad 
areas, and if our interpretation of the phenomena of Eastern Persia is correct, they 
have been extraordinarily active throughout the whole of Quatemar>' time. Thus 
interpreted the recent geological history of Persia begins with an arid climate at 
the end of the Tertiary era, after which ensued a fluvial period composed of some 
fifteen fluvial epochs of prolonged rivers and expanded lakes, separated by inter- 
fluvial epochs of shortened rivers and diminished lakes. The fluvial epochs increased 
in frequency and possibly in length and intensity from the beginning up to about 
the middle, after which they decreased. The evidence for these many epochs is of 
varying degrees of validity, and increases in certainty from first to last. The two 
lacustrine terraces of the various lakes and playas indicate two recent fluvial epochs. 
The kind of evidence and the method of study are of a sort which is ever)' where 
familiar and which has been successfully tested in many cases. The three preceding 
epochs rest on less effective evidence. The evidence for them in the three gravel 
strata at Sistan is not in itself conclusive, since it consists of but two or three 
sections ; and the warping and volcanic action which are known to have been taking 
place at the same time may have influenced the deposition of the gravels. Never- 
theless, the widespread occurrence of a series of five terraces in other localities, and 
the impossibility of explaining these except on the climatic theory, give a fair degree 
of reliability to the conclusion that three more severe fluvial epochs preceded the 
two recorded in the lake shores. The test of this conclusion lies in a further study 
of those regions where, according to theoretically deduced consequences, similar 
terraces ought to be found. 
The remaining ten epochs rest confessedly on a small basis of fact. It has been 
sunnised that the glacial period may have consisted of an increasing series of 
climatic changes preceding a decreasing series, and there is evidence that the exten- 
sion of the ice during what is commonly known as the second glacial epoch was 
greater than during its predecessor. Further than this, however, so far as I am 
aware, no one has ever gone. The facts of Sistan seem explicable only on the 
theory of a large number of increasingly severe fluvial epochs followed by an 
approximately equal series of decreasing epochs. This is at least a fair working 
hypothesis. To test the theory is difficult in the ver}- nature of the case. Yet it 
can be done. In the first place, a far more extensive study of the abundant deposits 
of Sistan is practicable to-day, and it is only a matter of time when it will be 
