milkiness to what, from its tint, would otherwise be a blue fluid. So rapid is the vegetation, owing to the decomposition of the carbonic acid, that, even in winter, masses of confervae and lichens, mixed with deposited travertine, are constantly detached by the currents of water from the bank and float down the stream, which being a considerable river is never without many of these small islands on its surface; they are sometimes only a few inches in size, and composed merely of dark-green confervae or purple or yellow lichens, but they are sometimes even of some feet in diameter, and contain seeds and various species of common water-plants, which are usually more or less encrusted with marble. There is, I believe, no place in the world where there is a more striking example of the opposition or contrast of the laws of animate and inanimate Nature, of the forces of inorganic chemical affinity and those of the powers of life. Vegetables in such a temperature, and everywhere surrounded by food, are produced with a wonderful rapidity, but the crystallisations are formed with equal quickness, and they are no sooner produced than they are destroyed together. Notwithstanding the sulphureous exhalations from the lake, the quantity of vegetable matter generated there and its heat make it the resort of an infinite variety of insect tribes, and even in the coldest days in winter numbers of flies may be observed on the vegetables surrounding its banks or on its floating island's, and a quantity of their larvae may be seen there sometimes encrusted and entirely destroyed by calcareous matter, which is likewise often the fate of the insects themselves, as well as of various species of shell-fish that are found amongst the vegetables, which grow and are destroyed in the travertine on its banks. Snipes, ducks, and various water-birds, often visit those lakes, probably attracted by the temperature and the quantity of food in which they abound; but they usually confine themselves to the banks, as the carbonic acid disengaged from the surface would be fatal to them if they ventured to swim upon it when tranquil. In May, 18--, I fixed a stick on a mass of travertine covered by the water, and I examined it in the beginning of the April following for the purpose of determining the nature of the depositions. The water was lower at this time, yet I had some difficulty, by means of a sharp-pointed hammer, in breaking the mass which adhered to the bottom of the stick; it was several inches in thickness. The upper part was a mixture of light tufa and the leaves of confervae; below this was a darker and more solid travertine, containing black and decomposed masses of confervae; in the inferior part the travertine was more solid and of a grey colour, but with cavities which I have no doubt were produced by the decomposition of vegetable matter. I have passed many hours, I may say many days, in studying the phenomena of this wonderful lake; it has