The peak of the Irazú is a point from which go various spurs and secondary mountains in opposite directions, one to the west and one to the east, the latter terminating in a crater where the Parismina River takes its origin. The western mountains trend first in a westerly direction to the Cerro Pelon, where they divide, one part descending south to the pass of Ochomogo, 1540 meters above sea-level; the other, after taking a northwesterly direction, terminating in the plain of La Palma, which is a part of the water-shed of the two oceans. On the south various mountains follow the rivers Pirris and Turialba. The Irazú has various craters, formed successively, each one contributing to the gradual rising of the mass. The Irazú, which had eruptions in 1723, 1726, 1821 and 1847, has now an altitude of 3414 m. (11,200 feet), and from its summit both oceans are visible, and also the great valleys of San Juan and of Lake Nicaragua, as well as the mountains of Pico Blanco, Chirripo, Buena Vista and Las Vueltas. Turialba had a famous eruption of sand and ashes which began on the 17th of August, 1864, and lasted to March, 1865. Its heaviest ejected matter fell to the west, and Seebach classifies it as andesite. Another eruption, occurring on February 6, 1866, was accompanied by heavy earthquakes and sent its ashes as far as Puntarenas. The Cordillera del Miravalles commences with the volcano Orosi, situated near the southwest extremity of Lake Nicaragua. In its southeast trend it recedes more and more from the lake and the San Juan River. It is an irregular, broad and volcano-dotted chain, about sixty geographical miles long, breaking down gradually on the northwest from Orosi to the Sapoa River, one of the southern boundaries of Nicaragua. In this short distance are found the Cerro de la Vieja (6508 feet), the Montemuerto (8000 feet), the beautiful volcano Tenorio (6700 feet), the volcanoes Miravalles (4665 feet), the Rincon (4498 feet), and the Orosi (5195 feet). These mountains, as far as they have been examined, are found to be of eruptive origin, basalts and trachytes predominating, but extensive sedimentary rock formations are also found upon their slopes, as well as vast deposits of boulders, clay, earth and volcanic material. The peninsula of Nicoya, forming a part of Guanacaste, is partly an elevated plain and partly consists of hills and mountain ridges seldom attaining a greater elevation than 1500 feet. It is also composed of eruptive rocks and sedimentary formations, the latter being especially visible in the valley of Tempisque. Between the northern volcanic section and the more regular Talamanca range is the notable “Ochomogo” Pass, about twenty miles broad, and a little more than 5000 feet above the sea-level at the water parting.