272 COSMOS. 



assiduity, partly from materials already published, and 

 partly from manuscript notes, upon the linear volcanoes 



uith Tables of the Comparative Heights of the Mountains in Central 

 America, 1852, vol. i, p. 418, and vol. ii, p. 102). The important work 

 which is promised us by Dr. Oerstedt, under the title of Schildernng 

 der Naturverhdltnisse von Nicaragua und Costa Rica, besides the 

 admirable botanical and geological disco verieKS which constitute the 

 primary object of the undertaking, will also throw light upon the 

 geognostic nat-ure of Central America. Dr. Oersted passed through 

 that region in various directions from 1846 to 1848, and brought 

 back a collection of rocks to Copenhagen. I am indebted to his 

 friendly communications for interesting corrections of my fragmen- 

 tary work. From a careful comparison of the materials with which I 

 am acquainted, including those collected by Hesse, the Prussian 

 Consul-General in Central America, which are of great value, I bring 

 together the volcanoes of Central America in the following manner, 

 proceeding from south to north : 



Above the central plateau of Cartago (4648 feet), in the republic of 

 Costa Rica (lat. 10 9') rise the three volcanoes of Turrialva, Irasu, and 

 Reventado, of which the first two are still ignited. 



Volcan de Turrialva* (height about 11,000 feet) is, according to 

 Oersted, only separated from the Irasu by a deep, narrow ravine. 

 Its summit, from which columns of smoke rise, has not yet been 

 ascended. 



The volcano Irasu*, also called the volcano of Cartago (11,100 feet) 

 to the north-east of the volcano Reventado, is the principal vent 

 of volcanic activity in Costa Rica, but still remarkably accessible, 

 and towards the south divided into terraces in such a manner that 

 one may on horseback, almost reach the elevated summit, from 

 which the two oceans, the sea of the Antilles and the Pacific, may be 

 geen at once. The cone of ashes and rapilli, which is about a thou- 

 sand feet in height, rises out of a wall of circumvallation (a crater of 

 elevation). In the flatter, north-eastern part of the summit, lies the 

 true crater, of 7500 feet in circumference, which has never emitted 

 lava-streams. Its eruptions of scoriae have often (1723, 1726, 1821, 

 1847) been accompanied by destructive earthquakes, the effect of 

 which has been felt from Nicaragua or Rivas to Panama (Oersted). 

 During a very recent ascent of the Irasu, in the beginning of May, 

 1855, by Dr. Carl Hoffmann, the crater of the summit and its 

 eruptive orifices have been more accurately investigated. The 

 altitude of the volcano is stated from a trigonometrical measure- 

 ment by Galindo, at 12,000 Spanish feet, or, taking the vara 

 ras.=0.43 of a toise, at 11,000 feet. (Bonplandia, Jahrgang, 1856, 

 No. 3). 



El Reventado (about 9500 feet), with a deep crater, of which the 

 southern margin has fallen in, and which was formerly filled with 

 water. 



