According to the tradition, the phenomena of small eruptions of water and mud which were observed during the first days simultaneously with the incandescent scoriæ, 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 elevated 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 1268. 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 place, 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 mountain 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 the superposed strata of the atmosphere. On descending from the central plateau of Mexico (whose mean elevation is 7460 feet), to the corn-fields of Valladolid de Michuacan, to the charming lake of Patzcuaro, with the inhabited islet Janicho and into the meadows around Santiago de Ario, which Bonpland and I found adorned with the dahlias which have since become so well known, we have not descended more than nine hundred or a thousand feet. But in passing from Ario on the steep declivity over Aguasarco into the level of the old plain of Jorullo, we diminish the absolute elevation in this short distance by from 3850 to 4250 feet'. The roundish, convex part of the upheaved plain is about 12,790 feet in diameter, so that its area is more than seven square miles. The true volcano of Jorullo and the five other mountains which rose simultaneously with it upon the same fissure, are so situated that only a small portion of the Malpais lies to the east of them. Towards the west, therefore, the number of hornitos is much larger, and when in early morning I issued from the Indian huts of the Playas de Jorullo, or ascended a portion of the Cerro del Mirador, I saw the black volcano projecting very picturesquely above the innumerable white columns of smoke of the "little ovens" (hornitos). Both the houses of the Playas and the basaltic hill Mirador are situated upon the level of the old non-volcanic, or, to speak more cautiously, un-upheaved soil. Its beautiful vegetation, in which a multitude of salvias bloom beneath the shade of a new species of fan palm (Corypha pumos), and of a new alder (Alnus Jorullensis), contrasts with the desert, naked aspect of the Malpais. The comparison of the height of the barometer at the point where the upheaval 7 My barometric measurements give for Mexico 1168 toises (7470 feet), Valladolid 1002 toises (6409 feet), Patzcuaro 1130 toises (7227 feet), Ario 994 toises (6358 feet), Aguasarco 780 toises (4089 feet), for the old plain of the Playas de Jorullo 404 toises (2584 feet) (Humboldt, Observ. Astron. vol. i, p. 327, Nivellement Barométrique, No. 366-370). 8 If the old plain of the Playas be 404 toises (2584 feet), I find for the maximum of convexity of the Malpais above the sea-level 487 toises (3115 feet); for the ridge of the great lava-stream 600 toises (3838 feet); for the highest margin of the crater 667 toises (4266 feet); for the lowest point of the crater at which we could establish the barometer 644 toises (4119 feet). Consequently the elevation of the summit of Jorullo above the old plain appeared to be 263 toises or 1682 feet. commences in the Playas, with that at the point immediately of the inner structure of the soil which I could examine at The many thousand small eruptive cones (properly rather of a roundish or somewhat elongated, oven-like form) which cover the upheaved surface pretty uniformly, are on the average 4 to 9 feet in height. They have risen almost ex9 Burkart, Aufenthalt und Reisen in Mexico in den Jahren, 18251834, Bd. i (1836), p. 227. 10 Op. cit. sup. Bd. i, pp. 227 and 230. 11 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), pp. 866-876, and 918-923: sur les éruptions et le drapeau de l'infaillibilité." See also, with regard to Jorullo, Carl Pieschel's instructive description of the volcanoes of Mexico, with illustrations by Dr. Gumprecht, in the Zeitschrift für 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 Republik Mexico, 1856, tab. 13, 14, and 15. The Royal Museum of Berlin, in the department of engravings and drawings, possesses a splendid and numerous collection of representations of the Mexican volcanoes (more than 40 sheets), taken from nature by Moritz Rugendas. Of the most western of all Mexican volcanoes, that of Colima alone, this great master has furnished fifteen coloured views. clusively on the western side of the great volcano, as indeed, the eastern part towards the Cerro de Cuiche, scarcely constitutesth 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 concentric shells; I was frequently able to count from 24 to 28 such shells. The balls are flattened into a somewhat spheroidal form, and are usually 15-18 inches in diameter, but vary from 1 to 3 feet. The black basaltic mass is penetrated by hot vapours and broken up into an earthy form, although the nucleus is of greater density, whilst the shells, when detached, exhibit yellow spots of oxide of iron. Even the soft, loamy mass which unites the balls is, singularly enough, divided into curved lamella, which wind through all the interstices of the balls. At the first glance I asked myself whether the whole, instead of weathered basaltic spheroids, containing but little olivine, did not perhaps present masses disturbed in the course of their formation. in opposition to this we have the analogy of the hills of globular basalt, mixed with layers of clay and marl, which are found, often of very small dimensions, in the central chain of Bohemia, sometimes isolated and sometimes crowning long basaltic ridges at both extremities. Some of the hornitos But are so much broken up, or have such large internal cavities, that mules when compelled to place their fore-feet upon the flatter ones, sink in deeply, whilst in similar experiments which I made, the hills constructed by the termites, resisted. In the basaltic mass of the hornitos I found no immersed scoriæ, or fragments of old rocks which had been penetrated, as is the case in the lavas of the great Jorullo. The appellation Hornos or Hornitos is especially justified by the circumstance that in each of them (I speak of the period when I travelled over the Playas de Jorullo and wrote my journal, 18 September, 1803,) the columns of smoke break out, not from the summit, but laterally. In the year 1780, cigars might still be lighted when they were fastened to a stick and pushed in to a depth of 2 or 3 inches; in some places the air was at that time so much heated by the vicinity of the hornitos, that it was necessary to turn away from one's proposed course. Notwithstanding the refrigeration which, according to the universal testimony of the Indians, the district had undergone within 20 years, I found the temperature in the fissures of the hornitos to range between 1990 and 203°; and at a distance of twenty feet from some hills, the temperature of the air was still 108°.5 and 116°.2, at a point where no vapours reached me; the true temperature of the atmosphere of the Playas being at the same time scarcely 77°. The weak sulphuric vapours decolorized strips of test paper, and rose visibly, for some hours after sunrise, to a height of fully 60 feet. The view of the columns of smoke was most remarkable early in a cool morning. Towards midday, and even after 11 o'clock, they had become very low and were visible only from their immediate vicinity. In the interior of many of the hornitos we heard a rushing sound like the fall of water. The small basaltic hornitos are, as already remarked, easily destructible. When Burkart visited the Malpais, 24 years after me, he found that none of the hornitos were still smoking; their temperature being in most cases the same as that of the surrounding air, while many of them had lost all regularity of form by heavy rains and meteoric influences. Near the principal volcano Burkart found small cones, which were composed of a brownish-red conglomerate of rounded or angular fragments of lava, and only loosely coherent. In the midst of the upheaved area, covered with hornitos, there is still to be seen a remnant of the old elevation on which the buildings of the farm of San Pedro rested. The hill, which I have indicated in my plan, forms a ridge directed east and west, and its preservation at the foot of the great volcano is most astonishing. Only a part of it is covered with dense sand (burnt rapilli). The projecting basaltic rock, grown over with ancient trunks of Ficus indica and Psidium, is, certainly, like that of the Cerro del Mirador and the high mountain masses which bound the plain to the eastward, to be regarded as having existed before the catastrophe. It remains for me to describe the vast fissure upon which a series of six volcanoes has risen, in the general direction from south-south-west to north-north-east. The partial direction of the first three, less elevated volcanoes situated most southerly is S.W-N.E.; that of the three following |