314 COSMOS. 



According to the tradition, the phenomena of small erup- 

 tions of water and mud which were observed during the 

 first days simultaneously with the incandescent scorias, are 

 ascribed to the destruction of two brooks, which, springing 

 on the western declivity of the mountain of Santa Ines, and 

 consequently to the east of the Cerro de Cuiche, abundantly 

 irrigated the cane-fields of the former Hacienda de San 

 Pedro de Jorullo, and flowed onwards far to the west to the 

 Hacienda de la Presentacion. Near their origin, the point 

 is still shown where they disappeared in a fissure with their 

 formerly cold waters, during the elevation of the eastern 

 border of the Malpais. Running below the Hornitos, they 

 reappear, according to the general opinion of the people of 

 the country, heated, in two thermal springs. As the ele- 

 \ ated part of the Malpais is there almost perpendicular, they 

 form two small waterfalls, which I have seen and represented 

 in my drawing. For each of them the previous name, Rio 

 de San Pedro and Rio de Cuitimba, has been retained. At 

 this point I found the temperature of the steaming water to 

 be 126'8. During their long course the waters are only 

 heated, but not acidulated. The test papers, which I usually 

 carried about with me, underwent no change ; but further 

 on, near the Hacienda de la Presentacion, towards the 

 Sierra de las Canoas, there flows a spring impregnated with 

 sulphuretted hydrogen gas, which forms a basin of 20 feet 

 in breadth. 



In order to acquire a clear notion of the complicated outline 

 and general form of the surface of the ground, in which such 

 remarkable upheavals have taken ^lace, we must distinguish 

 hypsometrically and morphologically : 1. The position of 

 the volcanic system of Jorullo in relation to the average level 

 of the Mexican plateau ; 2. The convexity of the Malpais, 

 which is covered by thousands of hornitos ; 3. The fissure 

 upon which six large, volcanic, mountain-masses have arisen. 



On the western portion of the Central Cordillera of Mexico, 

 which strikes from S.S.E. to N.N.W., the plain of the 

 Playas de Jorullo, at an elevation of only 2557 feet above 

 the level of the Pacific, forms one of the horizontal moun- 

 tain terraces, which, everywhere in the Cordilleras, interrupt 

 the line of inclination of the declivity, and consequently 

 more or less impede the decrease of heat in tho superposed 



