PIIYSIOGKAPIIV OF EASTERN PERSIA. 225 
ninninjT^ water or in playas when the lake floor was almost free from pennanent 
water, and hence during epochs of aridity. The green clays on the other hand 
are so fine-grained and uniform in texture and so free from changes of stnicture 
that they appear to be lacustrine deposits, laid down at a time when the lake was 
full of water, and hence during epochs of more abundant moisture. The entire 
formation of alternating reddish and green strata is most satisfactorily explained on 
the theon.- that it is the product of a series of climatic oscillations during which the 
lake was first dry and then full. The histor\- of the region after the volcanic erup- 
tions is recorded in gravel deposits which overlie the strata just described and 
alternate with fine gravel and in terraces which dissect all the strata. The gravels 
and terraces appear to indicate a continuation of the climatic oscillation down to 
ver)- recent times. The total number of oscillations amounts to fourteen or fifteen, 
and ma)' ha\"e been more. 
As one ascends from the bottom to the top of the deposits, the greenish layers 
iucrea.se in frequency and to a less extent in thickness up to a certain point, while 
the red layers become correspondingly thinner. After the green beds have reached 
their maximum development there is again a decrease in thickness which can be 
traced only through a few stages because the clays soon give place to gravels. The 
thickness of the layers is probably proportional to the length of time consumed in 
their accumulation. Therefore where the red laj-ers are thin, epochs of desiccation 
must have been short, and epochs of lake expansion must have prevailed for rela- 
tively long periods. Where the red layers are thick, on the contrary-, the epochs of 
desiccation must ha\e been longer and more important, and those of lake expansion 
must have been short. The meaning of the clays, the overlying gravels, and the 
terraces seems to be that the Ouaternar}- era in Persia consisted of a long series of 
increasingly strong climatic oscillations, followed by a nearly equal series of decrcas- 
ingly strong oscillations. The latter appear to correspond to the series of oscillations 
which we know as the glacial period in more northern countries. Furthermore, 
there is evidence, based on phjsiographic, archeological, and historical observations, 
which indicates that the last of the climatic oscillations may have been in progress 
during historical times. 
THE PHYSIOGRAPHY OF EASTERN PERSIA. 
Eastern Persia is a land of gra\el and nakedness, of huge desert basins and 
desolate, interminable slopes, of tantalizing mirages and bare mountains. Springs 
and fountains are things to dream of except directly among the mountains, and 
the traveler and his tired animals must be content with the brackish water of rare 
wells or the ]ioor brine of an ever-diminishing salt stream. Day after day one sees 
the same sad monotony of parched plains and lifeless mountains. At long intervals 
nomads pitch their black tents beside wretched wells and feed their sheep and 
camels on the sparse brown grass which springs up for a brief month at the end ot 
winter. The mountains are naked masses of rough, jagged rock, rising as islands 
in the midst of their own waste. Drought and aridity are ever\-where written 
large in the dearth of vegetation and in the verj- fonns that the earth itself 
