On the south side of the river Yura, in the locality called Calera, is found in layers or coats of considerable thickness, but of little extent, a limestone of a cellular and porous structure, composed in a great degree of very small and delicate tubes: their colour is a dirty white, and by all their signs and characters they appear to owe their origin to infiltration. From this stone is made the lime which is consumed in Arequipa and its neighbourhood. ANALYSIS OF THE MINERAL WATERS OF YURA. Mineral waters are distinguishable from common water by their taste, particular smell, colour, temperature more or less raised, and by their not being applicable to domestic purposes. They are found in different parts of the world in springs and wells: sometimes they are of the same temperature with the soil through which they pass, and at other times their temperature rises to the boiling point of water,—and then they are called thermal waters. In the countries where these waters appear, they had attracted the attention of the inhabitants since very remote times, and were medicinally employed internally as well as externally; but, since their component parts were but imperfectly known, they were often applied injudiciously, and they did not always obtain the reputation they merited, for their effects were sometimes contrary to those which the physicians desired to produce. At the close of the seventeenth century chemists began to discover the substances to which mineral waters owed their peculiar properties; and, since this happy era, they have made such rapid progress in science, that in the present day we are acquainted with many of these substances. This knowledge we owe to simple and more exact methods of analysis. Nature appears to have favoured in an especial manner the environs of Arequipa with thermal springs to cure those maladies to which its inhabitants are subject. This is, however, no more than might be expected, considering the variety of medicinal ingredients with which the waters become impregnated as they slowly percolate through beds of lava, or issue from the deep recesses of burning mountains. The baths of Yura are situated in a small and narrow glen, several leagues to the N.N.W. of the city, and only one league from the village of the same name,—which, according to my measurement, is one hundred and seventy Spanish yards (varas) above the square of Arequipa.[65]