The chief rivers in Arabia are occasioned by the rains, and are merely torrents which descend from the moun tains and continue to flow during the rainy season They seldom or never reach the ocean ; but arc soon swallow ed up in the arid plains, which surround them. Of this description is the Ostad, which rises in Ncdsjcd, and is represented by sonic travellers as an important river, falling into the Persian gulf. Those streams which run during the dry season, are at best but insignificant brooks ; the most considerable of which are, that which rises near Sana, and joins the Indian ocean below Har gia; and the Prim, which has its source in the desert of Mahhra, and falls into the same sea The Euphrates, and even the Tigris, are claimed by some geographers as Arabian rivers, but we see no good reason for adopt ing this opinion. The Tigris has no connection what ever with this country ; and a small proportion only of the Euphrates washes its northern boundary. This de ficiency of water in Arabia is severely felt by the inha bitants ; and to it must be attributed that general ap pearance of sterility and wildness so strikingly observ able throughout the greatest part of the peninsula.
The mountains form the most striking and gratifying objects in the Arabian landscape. Though some of them are craggy and precipitous, and rather unfavour able for agriculture, yet it is in their neighbourhood. only, that any appearance of fertility and cultivation ex ists. The principal range runs parallel to the Arabic gulf, and extends from the northern to the southern extremity of the peninsula. The mountains of Oman, which stretch into the sea, appear to be the continuation, of a range on the opposite side of the Persian gulf, whose summits form the islands of Ormus and Larek, in the mouth of that sea. In Hadramaut are the moun tains of Seger, famous for their frankincense ; and in Hedjas are Safra, remarkable for the balm of Mecca, and Gazvan, whose lofty top is continually covered with snow. Between the gulfs of Suez and Acaba, are the well-known mountains of Horeb and Sinai. Upon Sinai stands the monastery of St Catharine's, where the Greeks make an annual pilgrimage. In the steep ascent of the rock, the pilgrims have cut out steps by which they can ascend to the top; 3000 of these, Pococke reckons to be the height of the mountains.
Owing to the scarcity of water which pervades the whole of this country, and the sandy and parched nature of its soil, Arabia presents few objects of research to the natural historian ; forests indeed are to be met with only in the highland provinces, and are even there very infrequent. A considerable difficulty is occasioned to
botanical investigation, by the intense heat of the sun, which withers the flowers as soon as they are blown. Yet, from the diversity of its climate, which partakes of the advantages of the temperate and torrid zones, its productions, though not so numerous, are more various and uncommon than those of any other country. In the Flora-Arabica of Mr Forskal are to be found 30 new genera of plants unknown to European botanists ; and these plants, that are common to it with Europe, are generally of a different species. The most curious of the new genera are : Caydbeja or Forskalca, which grows in the driest places of the country. It has small feelers, with which it fixes itself so tenaciously upon smooth bodies, that it is torn in pieces before it can be removed. The Volutella resembles a small tender thread. It has neither root nor leaves, but entwines itself about trees, and bears berries, which are eaten by children. The Xerium Obesum, a sort of laurel rose, is remark able for a singular bulb close to the earth, about the size of a man's head, out of which the branches spring. Among the indigenous trees of Arabia, are the Catha, which is commonly planted among the coffee shrubs on the hills. The buds of this tree are chewed by the Arabians, as betel is by the Indians. They ascribe to it the virtue of assisting digestion, and use it as a preven tative against infectious distempers. The Keura is famous for its perfume, and has some resemblance to the palm-tree ; it bears flowers of a rich and delicious smell, which are sold at a very high price. But their most valuable trees are the coffee, which furnish the Arabians with their best article of exportation : And the Amyris Opobalsamum, which produces the balm of Mecca, the most costly of all the gum resins. The inhabitants are in many places unacquainted with its qualities, and only burn its wood as a perfume. This balm, according to Mr Bruce, a few centuries ago, when the Venetians carried on the India trade, by Alex andria, sold for its weight in gold ; but, owing to the quantity of similar drugs brought from the new world, is now of little value. Besides these, they have the cot ton tree, the cocoa tree, pomegranates, tamarinds, dates, apricots, peaches, almonds, filberts, and figs. Arabia produces also, in great abundance, gourds, cucumbers, pumpkins, and various kinds of melons, some of which grow spontaneously in the woods, and are often used for feeding camels.