The desert, however, does not always present the same aspect, or, consequently the same difficulties. In some parts I found it covered with rocks and gravel, which bore the traces of caravans that had passed long before. Besides, though the desert is a plain of sand and rock, the Arab commits few errors in crossing it, and is seldom wrong to the extent of half an hour in fixing the time of arrival at the wells. I ought not to omit to mention, that these wells are almost constantly found covered over, and that the first thing done on the arrival of a caravan is to clear away the sand. On the 6th of May we resumed our march, at three in the morning, and continued our route to the north. Still the same soil, the same aridity, and the same uniformity, as on the preceding days. The atmosphere was very heavy all day, and the heat excessive. It seemed as if we should have rain. The sun, concealed by clouds, appeared only at long intervals. But our prayers did not obtain from Heaven a drop of rain. In spite of all the prognostics no shower fell. The further northward we proceeded the more barren the country became. We no longer saw either thistles or salvadoras: sad consolations, where all nature wears so frightful an aspect! The plain had here the precise appearance of the ocean; perhaps such as the bed of a sea would have, if left by the water. In fact, the winds form in the sand undulating furrows, like the waves of the sea when a breeze slightly ruffles its surface. At the sight of this dismal spectacle, of this awful abandonment and nakedness, I forgot for a moment my hardships, to reflect on the violent convulsions which thus appeared to have dried up part of the ocean, and of the sudden catastrophes which have changed the face of our globe.