298 COSMOS. 



with that at the point immediately at the foot of the vol- 

 cano, gives 473 feet of relative perpendicular elevation. The 

 house that we inhabited stood only about 500 toises (3197 

 feet) from the border of the Malpais. At that place there 

 was a small perpendicular precipice of scarcely twelve feet 

 high, from which the heated water of the brook (Rio de San 

 Pedro) falls down. The portion of the inner structure of 

 the soil which I could examine at the precipice showed 

 black, horizontal, loamy strata, mixed with sand (rapilli). 

 At other points which I did not see, Burkart has observed 

 " on the perpendicular boundary of the upheaved soil, where 

 the ascent of this is difficult, a light gray and not very dense 

 (weathered) basalt, with numerous grains of olivin."* This 

 accurate and experienced observer has, however,! like myself, 

 on the spot conceived the idea of a vesicular upheaval of the 

 surface effected by elastic vapors, in opposition to the opinion 

 of celebrated geognosists,f who ascribe the convexity, which 

 I ascertained by direct measurement, solely to the greater 

 effusion of lava at the foot of the volcano. 



The many thousand small eruptive cones (properly rather 

 of a roundish or somewhat elongated, oven-like form), which 

 cover the upheavedsur face pretty uniformly, are on the 

 average four to nine feet in height. They have risen almost 

 exclusively on the western side of the great volcano, as in- 

 deed the eastern part, toward the Cerro de Cuiche, scarcely 

 constitutes J 3 th of the entire area of the vesicular elevation 

 of the Playas. Each of the numerous hornitos is composed 

 of weathered basaltic spheres, with fragments separated like 



* Burkart, Aufentkalt und Reisen in Mexico In den Jahren, 1825-1834, 

 bd. i. (1836), p. 227. f Op. cit. sup., bd. i., p. 227 arid 230. 



t Poulett Scrope, Considerations on Volcanoes, p. 267 ; Sir Charles 

 Lyell, Principles of Geology, 1853, p. 429; Manual of Geology, 1855, 

 p. 580; Daubeny on Volcanoes, p. 337. See also "on the elevation 

 hypothesis," Dana, Geology, in the United States Exploring Expedition, 

 vol. x., p. 369. Constant Prevost, in the Comptes rendus, t. xli. (1855), 

 p. 866-876, and 918-923 : sur les eruptions et le drapeau de linfailli- 

 bilite." See also, with regard to Jorullo, Carl Pieschel's instructive 

 description of the volcanoes of Mexico, with illustrations by Dr. Gum- 

 precht, in the Zeitsciirift fur Allg. Erdkunde of the Geographical Society 

 of Berlin (bd. vi., s. 490-517); and the newly-published picturesque 

 views in Pieschel's Atlas der Vulkane der Repiiblik Mexico, 1856, tab. 

 Ib, 14, and 15. The Eoyal Museum of Berlin, in the department of 

 engravings and drawings, possesses a splendid and numerous collec- 

 tion of representations of the Mexican volcanoes (more than forty 

 sheets), taken from nature by Moritz Eugendas. Of the most western 

 of all Mexican volcanoes, that of Coliina, alone, this great master has 

 furnished fifteen colored views. 



