This superabundance of reha, or carbonate of soda, which renders so much of the surface barren, must, I conclude, arise from deposits of common salt, or chloride of sodium. The water, as it percolates through these deposits towards the surface, becomes saturated with their alkaline salts; and, as it reaches the surface and becomes evaporated in the pure state, it leaves them behind at or near the surface. On its way to the surface, or at the surface, the chloride of sodium becomes decomposed by contact with _carbonates of ammonia and potassa--sulphuric and nitric acids_. In a soil well supplied with decaying animal or vegetable matter, these carbonates or sulphates of soda, as they rise to the surface, might be formed into nutriment for plants, and taken up by their roots; or in one well flooded occasionally with fresh water, any superabundance of the salts or their bases might be taken up in solution and carried off. The people say, that the soil in which these carbonates of soda (reha) abound, are more unmanageable than those in which nitrates abound: they tell me that, with flooding, irrigating, manuring, and well ploughing, they can manage to get crops from all but the soils in which this _reha_ abounds. The process above described, by which the bracelet makers extract the carbonates of soda and potash from the earth of the small, shallow tanks, is precisely the same as that by which they are brought from the deep bed of earth below and deposited on or near the surface. In both processes, the water which brings them near the surface goes off into the atmosphere in a pure state, and leaves the salts behind. To make soap from the reha, they must first remove the silex which it contains.