[16]The lakes have marshy borders, and high salt islands, as if formed by man, which however are natural, and, the people say, have existed since their remembrance. The saline materials are a carbonate and muriate of soda: we saw no incrustations on the bottom or surface: at this season, the same is the case in the Bahr-Trona, in Fezzan. Each lake is not more than half or three-fourths of a mile in circumference.—W. O.
[17]The hills run nearly north and south, edging a little to the westward; they have numerous small bays or recesses, which produce a fine echo; many places with saline incrustations, and some of the large black patches like the frozen surface of a recently ploughed field. Almost all the salt formations are in low, protected situations; the water is near; and, often in the very centre, you have fine fresh springs.—From whence is this salt derived? I have already suggested that the air has a powerful effect, and is a principal agent. There is no reason to believe there are large subterranean salt beds; if these existed to any great extent, we should not have the fresh springs so prevalent.—W. O.
[18]We had a fine wadey the greater part of the way, and many patches of saline incrustations; some exposed beds of red sandstone, containing numerous nodules of iron ore. Hills of much blacker colour; and a few have the appearance as of ruins of towns and castles, on their summits. Passed three springs, like the oozings at Traghen. A large tract of black surface, as if the situation of an extensive salt bed, from which the salt had only been removed a few years; it extends more than four or five miles to the eastward, and was more than a mile across, on our road. It is black and crispy, but has none of the irregular heapings taken notice of in other salt plains.
There is another small town about two miles to the westward, of the same name. Round it are a number of mud elevations, which appear as if produced by mud volcanoes; but these are artificial, and made for the preparation of salt. I had long wished to see the extensive salt plain that afforded such copious supplies: originally, no doubt, the large spaces I have several times noticed afforded abundance, but the re-production could not keep up with the quantity taken away. Art was employed to obtain Nature; shallow pits were dug, which soon filled with water, and its evaporation left thick layers of salt: high embankments were raised round these, evidently to prevent currents of air. These places have much the look of our tanyards, with small pits partitioned from each other. The water is now strongly impregnated; in summer a thick crust is formed, which is the salt in use. One of these works apparently yields a large quantity of salt every year. When removed, the sordes are heaped up on the embankments. In the recesses there are many stalactites, of a beautiful white colour, which consist of muriate and carbonate of soda.
The great mystery is, the origin of the salt in all situations in which the water is near the surface, and the inclemency of the water prevented by shelter. It is highly probable all this vast country was once a salt ocean; its height is nothing, considering its distance inland. What effect has the want, or almost want of rain,—for, as far as I can learn, no salt formations exist within the boundaries of the rains? There are many fine fresh springs issuing from the soil, and none of the wells are brackish; when the water, however, remains some time stagnant, it gets impregnated with saline matter.—W. O.
[19]Some curious tubular, hollow, coralliform productions were picked up in the sand: they appear of very recent formation, and evidently produced by rain and wind acting on the sand. The particles are most minute; when broken, the substance has a shining glassy appearance: some lie horizontally, but the general position is perpendicular. The external surface is rough: the size varies, both in length and circumference, from a few lines to an inch and a half in the latter, and from an inch to a foot in the former direction.
The wells are holes, about eighteen inches deep: the water has a slight taste of carbonate of soda, that was strong at first, but diminished greatly after some water had been drawn. The holes fill very fast. The saline impregnation arises, very probably, from the earth around falling, and being blown into the holes. Dibla is bounded on the north by black sandstone and quartz hills, which extend some way to the eastward; on the south by sand hills, and by a winding wadey on the east. In the middle there are several small conical hillocks with table-tops: the lower part is formed of a fine schistus, of different colours, that next the base light and white; over that, green, exactly resembling large well-dried leaves of plants, which separate into the finest layers; the top is a black bituminous matter, which crumbles into small pieces by the slightest touch: these hillocks are from thirty to forty feet high, the probable height of the valley in former days; and it is not unlikely that the bituminous matter is a vegetable deposit. There are a few acacias, but so few, that we could procure no firewood, and the camels very little food.
A number of round semi-vitrified small stones were found on the sands, which the people collected to use as bullets. The mode of formation appears the same as the coralliform substances I have mentioned. These substances, in great quantities, are said to be formed after the rains that every now and then occur in this quarter.
[20]There is grass in abundance, and small mounds covered with a tetrandrous plant, called suag: its fruit a small drupa, which is in great request in Bornou and Soudan, for removing sterility in females. Boo Khaloom related one instance of a female, who had been in that state eighteen years, but was cured by the fruit. It is sweetish and hot to the taste, approaching to the Sisymbrium nasturtium. In passing the plant, a heavy narcotic smell is always perceived.—W. O.
[21]There is a very common grass which is grievously annoying from the prickles on its husk: it adheres to the dress and penetrates the skin. There is not one prickle, but the calyx is studded round, and they fasten themselves like grappling irons. These prickles may be considered one of the pests of the country: there is scarcely a place free from them. Our dog Niger is unable to walk, for they have got between his toes, and are adhering to every part of his long silken hair.