PRESENT CONDITION RIVERS OF MECHOACAN. 289 



found the temperature of the hot spring very low, — a fact which 

 seems clearly to indicate the gradual congelation of a subjacent bed 

 of lava which, from its immense thickness, may have been enabled 

 to retain its heat for half a century. The reader may be reminded, 

 that when we thus suppose the lava near the volcano to have been, 

 together with the ejected ashes, more than 500 feet in depth, we 

 merely assign a thickness which the current of Skaptar Jokul 

 attained in some places in 1783. 



"Another argument adduced in the support of the theory of infla- 

 tion from below, was, the hollow sound made by the steps of a horse 

 upon the plain ; which, however, proves nothing more than that the 

 materials of which the convex mass is composed are light and 

 porous. The sound called " rimbombo" by the Italians, is very 

 commonly returned by made ground when sharply struck, and has 

 been observed not only on the sides of Vesuvius and of other vol- 

 canic cones where a cavity is below, but also in plains, such as the 

 Campagna di Roma, composed in a great measure of tuff and other 

 porous and volcanic rocks. The reverberation, however, may be 

 assisted by grottoes and caverns, for these may be as numerous in 

 the lavas of Jorullo as in many of those of Etna; but their exist- 

 ence would lend no countenance to the hypothesis of a great arched 

 cavity, four square miles in extent, and in the centre 550 feet high. 1 



" Mr. Burkhart, a German director of mines, who examined Jo- 

 rullo in 1827, ascertained that there had been no eruption there 

 since Humboldt's visit in 1803. He went to the bottom of the 

 crater, and observed a slight evolution of sulphurous acid vapors, 

 but the "hornitos" had ceased entirely to give forth steam. Dur- 

 ing the twenty-four years intervening between his visit and that of 

 Humboldt, vegetation had made great progress on the flanks of the 

 new hills, and the rich soil of the surrounding country was once 

 more covered, with luxuriant crops of sugar cane and indigo, and 

 there was ' an abundant growth of natural underwood on all the 

 uncultivated tracts." 2 



The State of Mechoacan is extraordinarily rich in rivers and 

 streams. The Lerma, Balsas, Zitacuaro, Huetamo, Cluranueco, 

 Marquez, Aztala, Tlalpujahua, and some smaller streamlets and 

 brooks are found in its vallies ; while the lakes and ponds of Cuizco 

 or Aaron, Patzcuaro, Huango, Tanguato, and Huaniqueo afford 



1 See Scrope on Volcanoes, p. 267. 



2 Leonhard and Brown's Neues Jarbuch, 1835, p. 36. See Lyell's Geol., Am 

 Ed., 1 vol., p. 345. 



