1859.] SCEOPE CONES AND CEATEES. 545 



authorities so eminent in the present day as MM. de Humboldt, de 

 Buch, de Beaumont, and Dufrenoy. 



To recapitulate. My argument then is, that the '^elevation-crater" 

 or '^ upheaval " theory, as applied to volcanic action by MM. de 

 Humboldt, de Buch, de Beaumont, and Dufrenoy, and to some ex- 

 tent by Dr. Daubeny and Professor James Forbes, as well as in 

 several popular geological compilations, is an assumption irrecon- 

 cileable with the appearances it professes to account for, and wholly 

 hypothetical — such a process never having been witnessed; while 

 there is nothing in the form, structure, or composition of any of the 

 cones or craters to which it is applied by its advocates inconsistent 

 with the supposition that they owe their origin to the simple, ordi- 

 nary, normal, and perfectly intelligible phenomena of volcanic erup- 

 tions, as witnessed repeatedly by competent observers as well in the 

 present day as through all past historical times. 



Such eruptions, where they break out on new points of the sur- 

 face, are seen to throw up large quantities of scoriae, fragmentary 

 blocks, and ashes, which accumulate (as they fall) into conical hills, 

 having generally a circular depression in the centre or at the sum- 

 mit, the cause of which I have already explained. The com- 

 ponent layers of these hiUs have always, and, from their mode of 

 formation, necessarily, a quaquaversal outward dip, and occasionally 

 also a double or anticKnal concentric arrangement. And the same 

 disposition of the fragmentary ejectamenta is likely to take place, 

 and appears in fact to have taken place, when the eruption was 

 submarine as when it was subaerial, except so far as the weight and 

 resistance of the water above, or the wash of waves or currents, 

 have modified it. The lavas simultaneously protruded during such 

 eruptions take a course determined by their fluidity and specific 

 gravity and the form of the neighbouring surfaces : — where their 

 fluidity and specific gravity are both considerable, as in the fine- 

 grained basaltic lavas, and the adjoining surface-levels favourable, 

 spreading widely, or flowing to great distances, in comparatively 

 shallow sheets or streams ; where the fluidity is less, accumulating 

 in thicker beds in the vicinity of the orifice of eruption ; where it is 

 at the minimum (as in the case of the highly vitreous and conse- 

 quently viscous, or the spongy and porous trachytes), heaping itself 

 up above the vent in bosses, hummocks, or dome-shaped masses, 

 just as any very viscid liquid in ebullition, like paste or pudding, 

 will coagulate in lumpy excrescences above any crevice in the con- 

 taining vessel through which it can force a partial escape. 



Where eruptions habitually or frequently take place from the 

 same vent, it is obvious how the repetition of such a process as 

 has been described in the case of single eruptions must cause the 

 formation of a mountainous excrescence, approaching to a coni- 

 cal form, composed of the accumulated products, both fragmentary 

 and solid, arranged more or less irregularly (according as they may 

 be subjected during, or in the intervals of, the eruptions to more 

 or less of atmospheric, or in some cases marine, degradation), 



