MY first excursion to Tivoli was in the beginning of March; I have lately paid it a second visit, in part of a more extended ramble; and I shall give you the account of both excursions together. We leave Rome by the Porta San Lorenzo, but I say nothing concerning the antiquities in the immediate neighbourhood, as I have written enough about them to tire out your patience. After we had passed the Ponte Mammolo, the soil continues for some miles to consist of a decomposed tufo, rather sandy, but one would think not unfitted for vegetation, yet there is little corn, and the land is mostly sheepwalk, which in a country and climate too dry for perennial grasses to flourish, cannot be very productive. The near scenes are dreary enough, and a heavy atmosphere shut out the distant objects. A little way on the left of the road, about ten miles from Rome, is an old castle of the Borghese family, which nobody visits, for antiquities of the middle ages have no interest here. There are many fragments scattered about over this, and every other part of the Campagna, but it would require a book to describe them all; and no small ingenuity, to determine the nature of the edifices of which they have formed part.[8] About twelve miles from Rome is a little pool among bushes on the left, called Lago de’ Tartari. It is a mere pond of muddy yellowish water, with little or no peculiar taste, and neither receiving nor emitting any stream. The water deposits a copious crust of limestone upon all substances in it. It varies very much in height at different seasons, and the whole soil around is formed of its deposits: wherever the ground is broken we perceive bundles of pipes, and here and there a bit of reed remaining in the pipe, and proving the mode of its formation: above these pipes is generally a confused mass, deposited apparently on decaying fragments of vegetables. This sort of soil extends for a considerable distance, and as you may suppose, is incapable of cultivation; yet a few bushes grow on it, and abundance of the _Senecio leucanthemifolius_, and of some other plants not very common. On leaving this soil we pass on to another deposit of a substance less hard, and said to contain sulphur, or sulphuric acid, but nearly equally barren, and of much greater extent; about the middle, a stream of sulphureous water crosses the road, slightly warm, pretty clear, of a blue colour, and exhaling an odour which is perceived at a considerable distance. The taste is sulphureous, and I should say saltish, but Mr. P. D. called it acid. We left the carriage and walked up the stream; and at a little distance from the road, were surprised to see several branches separating themselves from the principal stream, and losing themselves in hollows of the ground. All these streams, which deposit considerable quantities of stony matter, form about them, not a continuous solid mass, but one full of caverns and hollows, extending in all directions.