By order of Don Francisco Pizarro, the city was founded in the year 1540. It suffered severely from the great earthquakes of the years 1582, 1600, 1604, 1687, 1715, and 1784.[62] All about Arequipa is a volcanic country, of which the natural history is very interesting, as may be learned from the following account, taken from an essay originally written and published in Spanish by Don Mariano Rivero, director-general of the mining department in Peru. This essay is deficient in minute chemical analysis; but it has the recommendation of being the only one, so far as we know, that has been written by a native Peruvian on the subjects which it embraces. TRANSLATION. GEOGNOSTIC DESCRIPTION. All the environs of the city of Arequipa are composed of volcanic products; so much is this the case that its edifices are constructed of a white and very light rock, rough to the touch, which contains pieces of pumice-stone and lava. It is called in the country _piedra sillar_, and, in fact, is a real trachyte (traquito). It is met with in different places, at the distance of several leagues from the city,—as, for example, in the glen through which passes the road of Islay. In the route which leads to the glen of Yura, over and above the loose pieces and sand, we meet the trachyte porphyry, not only in large detached masses, but also forming portions of the soil. The principal mass is compact, of a greyish black colour, with crystals of white vitreous felspar, and spangles of bronzed mica; it passes by decomposition into an ash-coloured trachyte, less hard than the first, and very rough to the touch: the crystals of felspar and mica suffer no decomposition. The adjacent hills are formed of rocks such as these, without presenting a decided stratification. At various points there appears a rock which, from its grain, its little hardness, the pieces of trachyte it contains, and its reddish colour, would seem to be a conglomerate of aqueous formation. The waters which run through rocky passes give rise to deep excavations, and with much good reason these parts (along which there is a road) are denominated _narrows_,—for they are only a yard and a half broad. The way is intersected at various points by ravines, (quebradas,) through which several small streams descend from the snowy mountain called Chachani. About a league before we reach Yura, and on the opposite side of the glen, there is an horizontal stratification which extends towards the west, presenting an interesting contrast with the Cordillera on the east, and the hills on the side of the valley along which we pass to Yura.