1859.] SCROPE CONES AND CEATERS. 511 



asperities of this great lava-bed tossed up bj jets of escaping steam, 

 and coated over to the depth of a foot or two by a black mud formed 

 from the showers of volcanic ashes mixed with rain-water, which 

 are recorded to have fallen in abundance during and after the erup- 

 tion ; in which superficial mud or claj the influence of the hot 

 vapours escaping through them had produced a concentric concre- 

 tionary arrangement of particles, such as is often found under similar 

 circumstances in volcanic ash or ^'wacke." Indeed this crust was 

 so brittle that Humboldt says the feet of the mules broke through 

 it. Consequently, I argued, it was quite unnecessary, for the purpose 

 of explaining the visible results of the eruption of Jorullo in 1759, to 

 imagine a new and unexampled mode of volcanic action, such as the 

 sudden inflation from beneath of a tract of solid horizontal strata 

 into a hollow bladder four square-miles in extent, with other sup- 

 posed hollow bubbles, large and small, upon its surface. 



It was too much, perhaps, to expect that any arguments pro- 

 ceeding from me, an unknown writer at that time (more than thirty 

 years back), should prevail against so great and deservedly esteemed 

 an authority as M. de Humboldt, especially upon a question relating 

 to a volcanic district which he had, as it were, discovered, and which 

 I had not even visited. Neither is it to be wondered at that this 

 notion of the inflation of volcanic hills, like bladders, from beneath, 

 having been thus presented to geologists in the character of an 

 observed fact, should have been applied by other writers as well as 

 by M. de Humboldt himself to many other volcanic formations. In 

 fact, from this supposed example, the theory of upheaval craters 

 (Erhebungskrater), shortly afterwards put forth by Humboldt's 

 compatriot and frequent correspondent, Leopold de Buch, readily 

 and naturally originated. The vaulted crust of the Malpais is, of 

 course, a half- elevated volcanic cone, only needing a Kttle more 

 " pushing up" to become an Etna, a Chimborazo, or an Elburz, in the 

 imagination of the upheavalists. Nevertheless, so thoroughly per- 

 suaded am I that M. de Humboldt is completely in error as to this 

 typical example, that I should be quite willing to rest the whole con- 

 troversy between the rival theories of upheaval and eruption upon this 

 single case*. I stop for a moment to mention, as a parallel example 

 to that of Jorullo, tending to show its very normal and ordinary cha- 

 racter, the results of a great eruption of the volcano of Awatscha 

 in Kamschatka in July 1827, visited by Messrs. Portel and Lenz in 

 the subsequent year. They describe a vast stream of trachytic lava 

 as having descended from the rim of the great crater of the moun- 

 tain, down whose outer flank it now projects in a steep ridge (evidently, 

 therefore, resembling the promontory of lava on the side of Jorullo). 

 At the base of the cone it spread out widely in a high platform, 



* Jorullo has recently been visited, at the request of M. de Humboldt, by M. de 

 Saussure ; and I understand from Sir Charles LjeU that the latter geologist has 

 communicated to him his conviction that upheaval played no part in its produc- 

 tion, and that an abundant stream of lava had flowed from its crater and deluged 

 the plain at its foot. M. de Saussure will, no doubt, before long publish his 

 observations in detail. 



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