The climate of the Crau presents contrasts most extreme. In winter the
thermometer falls and remains below zero for many nights in succession, and
the glacial _bise_ sweeps over the face of the desert, curdling the blood;
the flocks and herds seek shelter from this blast behind the long walls of
dry stones, which sometimes the violence of the wind throws down upon them.

During the summer the phenomenon of the mirage is almost continuous. The
bed of air in contact with the surface of stones scorched by the blazing
sun becomes rarified and dilated, so that the horizon appears to be fringed
on all sides with lakes of rippling water, most deceptive and tantalising
to the eye of the traveller.

The troops of wandering bulls and wild horses, flights of rose-coloured
flamingoes, of partridges and wild ducks give this region a pronounced
oriental physiognomy, and however painful it may be at such a time to
traverse this burning plain, it affords a curious picture of the Sahara in
miniature nowhere else to be seen in Europe.

The great scourge of the Crau is the north-west wind, the _bise_, the black
boreas of the ancients, so violent as to roll over the pebbles, and to blow
away the roofs of houses, and tear up trees by the roots. In fact, the Crau
may be regarded as the Home of the Winds.

It is easy to explain the origin of these furious gales, _bise_ and
_mistral_. The low sandy regions at the mouth of the Rhone, denuded of all
vegetation, and the great stony plain of the Crau, heated by the direct
rays of the sun, rarify the air over the surface of the soil, and this
rises, to be at once replaced by the cold air from the Alps and Cevennes;
the air off the snow pours down with headlong violence to occupy the vacuum