296 COSMOS. 



mountain" was seen to rise gradually for months or years, or 

 whether it appeared from the very first as an elevated peak, 

 no answer could be obtained. Riano's assertion that farther 

 eruptions had taken place in the first sixteen or seventeen 

 years, and therefore up to 1776, was declared to be untrue. 

 According to the tradition, the phenomena of small eruptions 

 of water and mud which were observed during the first days 

 simultaneously with the incandescent scorios 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 onward far to the west to the Hacienda de la Pre- 

 sentation. 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 elevated part of the Malpais is 

 there almost perpendicular, they form two small water-falls, 

 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 acid- 

 ulated. The test papers, which I usually carried about with 

 me, underwent no change ; but farther on, near the Hacienda 

 de la Presentation, toward the Sierra de las Canoas, there 

 flows a spring impregnated with sulphureted hydrogen gas, 

 which forms a basin of 20 feet in breadth. 



In order to acquire a clear notion of the complicated out- 

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

 such remarkable upheavals have taken place, we must dis- 

 tinguish hypsometrically and morphologically: 1. The po- 

 sition of the volcanic system of Jorullo in relation to the av- 

 erage 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 Mex- 

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

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

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

 ain terraces which every where in the Cordilleras interrupt 



