It is not less worthy the admiration of a geologist to behold, amid so much arid nakedness, the bottom of the deep glen of Yura clothed with pure green and cheering verdure, which comforts the pilgrim, and serves as a soothing restorative to the sick who, sacrificing their domestic comforts and the pleasures of society, go in search of health to the baths situated in this solitary spot. The glen of Yura, which stretches in the direction of from east to west, is in many parts extremely narrow, as at the site of the baths: but towards the Calera it opens up; and its inhabitants take advantage of this space to cultivate lucern, and collect the sub-carbonate of soda, improperly called saltpetre, which they use in manufacturing the soap consumed in Arequipa.[63] Having passed the distance of one thousand yards, the glen again becomes narrow, until it joins with the ravine of the river of Yura, which flows from the north-east to south-west. From this place it becomes deeper and narrower, and immediately follows a westerly direction. A rivulet formed by the junction of the smaller streamlets which arise in the hill called Horqueta irrigates some land in the strath beneath; and, pursuing its course to the baths, passes them at a yard’s distance, (now ceasing to be pure water,) to unite itself with the many jets that spring up a little above the baths, as I have seen in a ditch recently opened. This rivulet follows the course of the glen; and its waters, being impregnated with saline ingredients, irrigate the lucern fields, and contribute to increase the supply of the carbonate of soda. It at length joins the river of Yura, which during the periodical rains is in the highest degree dangerous to ford, on account of its strong current, and the many stones it carries along its impetuous stream. In the glen of Yura, as well as in the ravine alluded to, the different sorts of earth are of volcanic and transition formation: the first extend to a hundred paces beyond the ferruginous baths; the prevailing rock is trachyte, of a light ash-colour, with pieces of white felspar half decomposed, pumice-stone, and scales of black mica.