278 Rev. H. B. Tristram on the 



Sometimes a hard pebbly surface permits a canter for hours 

 over the level plain amidst dwarf, leafless, dust-coloured shrubs. 

 Perhaps on surmounting a ridge, the mirage of a vast lake 

 glittering in the sunshine excites both the horse and his rider. 

 On, on, gallops the wiry little steed over sand hard and crisp, 

 and coated with a delicate crust of saltpetre, the deposit of the 

 water, which at rare intervals has accumulated there, and formed 

 the Chotts and Sebkhas of the Desert. Occasionally the traveller 

 is gladdened and refreshed by pitching his camp in a Dayat, or 

 reposing for a few nights under the palm-trees of an Oasis. 



Each of these — the rocky ridges, the sand-drifts, the plains, 

 the Chotts or salt-plains, the Dayats, and the Oases — have their 

 peculiar ornithological characteristics. But by far the most in- 

 teresting portions of these regions are, as might have been anti- 

 cipated, the Dayats and Oases. The Dayat may be looked upon 

 as an unimprovable oasis, in which there is no constant supply 

 of water to be found at any depth, but where, from the con- 

 figuration of the substratum of limestone, — it being in fact de- 

 pressed into something like a saucer, — moisture gathers after 

 the rare and uncertain thunder-storms. This moisture affords 

 just sufficient support for a few Terebinth-trees [Pistacia atlan- 

 tica) and wild Jujubes [Zizyphus spina Chi'isti), under whose 

 shade a scanty herbage, intermingled with such desert plants as 

 the StaticcE, the Sisyjnbrice, Neurada procumbens, Bunias pro- 

 strata, Brassica lyrata, Cleome arahica, Hippocrepis comosa, is 

 browsed upon by troops of gazelles and a few antelopes. In 

 the Oases, on the contrary, water may always be relied upon at 

 a depth varying from 40 to 80 yards in the deposit of sand 

 immediately overlying the limestone, and said by the Arabs to 

 form underground streams, though it never rises to the sui*face 

 without the aid of Artesian wells *. 



Here are the winter-quarters of many of our familiar summer 

 visitants. The Chiffchaff, Willow Wren, and \^liitethroat hop 

 on every twig in the gardens shadowed by the never-failing 

 Palm. The Swallow and Window Martin thread the lanes and 



* It is interesting to note, that the theor)* and practice of Artesian wells 

 seem to have been well known to the tribes of the Desert for many centu- 

 ries, as is recorded by the Arab historians. 



