“When I wrote you last, I was just on the eve of departure for the Tuarick country, and in about a fortnight from this date, I hope we shall be on our way to Bornou. We found our journey to Ghaat very pleasant, and our reception very flattering. We were among a brave and warlike race, exceedingly superstitious; yet they were sensible; and though remarkably strict Mahometans, yet liberal in their ideas. The geology and botany of the country are nearly the same as in Fezzan, which I cannot enter upon at present. We made long excursions in the Wady (valley) Ghrurbi, and Wady Shiati, which Captain Lyon incorrectly joins. In our course we examined the Trona Lake, which is situated among amazingly high sand hills, running for several hundreds of miles to the westward, and lie between the Wadies Shiati and Ghrurbi. The lake is in a small valley which runs nearly E.S.E. and W.N.W. The north and south sides are bounded by hills of sand about 400 feet high. The bottom of the lake is a fine sand, on which is found the _cegoul_, (apparently a species of silex) and a downy grass. Near the place where we entered the valley there is a cluster of date palm trees, and a small lake from which impure Trona is obtained. On the western side is the Trona lake, surrounded by date trees, and its banks covered, on almost all sides, with the grass I have mentioned, and a tall juncus. It is almost half a mile long, and nearly 200 yards wide, of very inconsiderable depth at present (July) from the evaporation of the water, and many places are now dry which are covered in the winter and spring. The Trona is deposited in cakes at the bottom of the lake when the water is sufficiently saturated. The cakes are of various degrees of thickness, from a mere film to several inches. The thickest I could find was not more than three quarters of an inch, but at the beginning of the winter, when the water begins to increase, it is of the thickness I have mentioned, and is then said to be ripe. The surface next the bottom is not unequal from crystallization, but rough to the feel on account of numerous asperities. The upper surface is generally found studded with small beautiful cubical crystals of muriate of soda; the line of junction is always distinct, and one crystal is easily separated from another; when not covered with the muriate of soda, this upper surface is composed of a congeries of small tabular pieces, joined in every position. When the mass is broken, there is a fine display of circular crystals often radiated. The surface of the water is covered in many places with large thin sheets of _carbo-muriate of soda_, giving the whole the appearance of a lake partially frozen over; film after film forms till the whole is a considerable thickness. The soil of the lake is a dark barren sand approaching to black, of a viscid consistence and strong smell; and on the recently uncovered surface, near the banks, a black substance like mineral tar is seen oozing out.