CHAPTER XLIII. 
THE CAMELS BREAK DOWN 
’RIL 25th. As a consequence of the limpid purity 
of the atmosphere, the minimum thermometer sank 
to an unusually low level, not more than a couple of 
degrees above freezing-point ; and in the morning a nor’- 
wester was blowing and the air was again thick with dust. 
All day long therefore the temperature remained more 
than ordinarily low ; we had no grounds for complaining 
of the heat, even at noon. Under the clear night sky 
radiation had been very active ; then came the veil of 
dust, shielding the earth like an umbrella, so that the sun’s 
rays were a long time in warming the ground. Meanwhile 
the air grew so thick, that we had difficulty in seeing 
beyond the next dune or so. 
The terraced patches of clay and silt, which lay 
embedded between the sand-dunes, and on which we pre- 
ferred if possible to encamp, were formations of a remark- 
able character. They consisted of a series of horizontal 
flakes of clay, brittle, friable, and saline, and crumbled 
to pieces at the least touch. The several flakes did not 
lie at the same level, but generally rose layer above layer 
like a series of steps. There was not a trace of sand in 
them, nor of vegetable matter either. They were pure 
alluvial clays ; of that there could not exist a doubt. 
Probably they were the last surviving fragments of the 
bed of the great Central Asian Mediterranean, which 
has dried up in the course of countless centuries, and the 
different terraces possibly indicated different sea-levels. 
As a rule none of these patches of clay was bigger 
than the deck of a brig; and the sand-dunes in their 
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