ANNUAL OF SCIENTIFIC DISCOVERY. 



prism. Besides these products, there is found scoria, composed of melted 

 sulphur and ashes of pyroxene and dolerite, more or less calcined or altered 

 by the action of the watery vapors. 



ON THE MODE OF FORMATION OF VOLCANIC CONES AND CRATERS. 



In a paper presented to the Geological Society (London) by Mr. G. Poulett 

 Scrope, the author combated the doctrine originated by Humboldt, Von 

 Buch, de Beaumont, and others, which denies altogether that volcanic moun- 

 tains have been formed by accumulations of eruptive matters, and attributes 

 them solely to a sudden " bubble-shaped swelling up " of preexisting hori- 

 zontal strata, the bubble sometimes bursting at the top and then leaving its 

 broken sides tilted up around a hollow (elevation crater). The author ex- 

 pressed his belief that this notion originated in Humboldt's account of the 

 eruption of Jorullo, in 1759, in which a great error had been committed 

 the convexity of the hill being simply a bulky bed of lava poured out on a 

 flat plain from five ordinary cones of eruption. But the idea of a " bladder- 

 like swelling up " of horizontal strata into volcanic hills being thus started 

 by Humboldt, it was further extended by Von Buch, and hence arose the 

 crater-elevation" theory. Mr. Scrope then proceeds to show that the 

 characters of all volcanic mountains and rocks are simply and naturally to be 

 accounted for by their eruptive origin, the lavas and fragmentary matters 

 accumulating round the vent in forms determined in great decree by the 

 more or less imperfect fluidity of the former, which, as in case of some 

 trachytic lavas, glassy or spongy, may and do congeal in domes or bulky 

 masses immediately over, or in thick beds near the vent, or, as in that of 

 some basaltic lavas, may flow over very moderate declivities to great dis- 

 tances; and consequently that the upheaval or elevation-crater theory is a 

 gratuitous assumption, unsupported by direct observation, and contrary to 

 the evidence of facts. He concludes by representing its continued acceptance 

 be discreditable to science, and an impediment to the progress of sound 

 geology, masmuch as false ideas of the bubble-like inflation, at one stroke 

 such mountains as Etna or Chimborazo, must seriously affect all our spec- 

 ulations on geological dynamics, and on the nature of the subterranean 

 forces by which other mountain-ranges or continents are formed 



Conical Form of Volcanoes. -Sir Charles Lyell, in a paper recently read 

 before the Royal Institution (London), infers, from two recent excursions to 

 Etna, that the discovery of lava being capable of forming continuous and 

 tabular masses of crystalline rock on steep slopes, often exceeding thirty 

 egrees, enables us henceforth to dispense with that paroxysmal and termini 

 upheaval, which the advocates of " craters of elevation " legitimately deduced 

 from their premises; for it was as necessary for them, so long as the volcanic 

 beds were assumed to have been originally horizontal, to ascribe the whole 

 evation to a force acting from below, as it would have been if the upper- 

 most layers of each volcanic mountain could be assumed to be of marine 

 origin. In opposition to such a doctrine, Sir C. Lyell maintains that mechan- 

 >rce has nowhere played such a dominant part in the cone-making 

 5 to warrant our applying any other term save that of " cones of 

 eruption" to volcanic mountains in general. 



In conclusion, the lecturer gave a brief sketch of the scries of geolo-ir-al 

 \-hi-h he supposed to have occurred on the site of Etna since" the 

 mm: of the carUest eruptions, events wiiicli may have 



