Note 19 — Chapter I · FROM MOURZUK TO KOUKA IN BORNOU.
Reading edition
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.