Geological Society. 



cones and craters of the Phlegrjean fields to be due only to upheaval. 

 They offer no reliable test by which upheaved can be distinguished 

 from eruptive cones; or, when they attempt this, differ again from 

 one another, and even from themselves. Thus, von Buch considers 

 the extreme regularity of the slopes of Etna a proof of its upheaval. 

 M. de Beaumont asserts regularity of outline to be the distinguish- 

 ing feature of an eruptive cone, and yet declares the upper and the 

 lower portions of Etna, which are its least symmetrical parts, to be 

 of eruptive origin, and the intermediate cone, the slope of which is 

 extremely regular, to have been upheaved ! In respect to the tuff- 

 cones and cratei"s of the Phlegrsean fields, the series from Somma to 

 the Monte Nuovo is so evidently of similar character, that, to avoid 

 classing the first as an eruption-cone, the upheavalists have been 

 driven to deny that the Monte Nuovo itself was the product of erup- 

 tion, and even to assert that it existed in the Roman era, and was 

 only sprinkled with a few ashes by the eruption which, from all 

 contemporary authorities, threw it up in two days of the year 1538 ! 

 The author describes the circular anticlinal dip of the strata of the 

 Monte Nuovo and other tuff-cones of the Campi Phlegrsei as utterly 

 inexplicable upon the theory of upheaval, while it is the natural re- 

 sult of the fall and accumulation of fragmentary materials projected 

 upwards by eruptions. 



He then disputes the truth of M. de Beaumont's dogma, that lava 

 cannot consolidate into a solid bed upon a slope exceeding 5° or 6°, 

 and shows, from numberless instances in Auvergne and the Viva- 

 rais, on Etna, Vesuvius, Teneriffe, &c., that bulky beds of lava have 

 congealed on steep slopes, — in some cases, as for example in that of 

 Jorullo itself, in the form of a massive promontory projecting far 

 from the side of the cone from the crater of which it issued ; in 

 others, when liquidity was at the minimum, in that of a dome or 

 bell (Bourbon, Puy de Dome, &c.). In regard to Etna, he leaves 

 M. de Beaumont's misrepresentations of fact to be dealt with by Sir 

 C. Lyell, only remarking that, on M. de Beaumont's own showing, 

 the portion of Etna which he supposes to have been upheaved, is 

 positively " encrusted with a coating of lavas." 



The inapplicability of the elevation-theory to the Cantal, Mt. 

 Dore, and Mezenc in France is then shown, inasmuch as, by M. de 

 Beaumont's own admission, the angle of slope of their basaltic and 

 trachytic beds is even less than that of the recent and acknowledged 

 lava-flows in the same district. Finally, he asks what has become of 

 the products of the repeated eruptions of volcanos, if they have not 

 accumulated in the course of ages into the mountains which we find 

 there, composed of irregular alternating beds of lava and conglo- 

 merate just such as we see to be erupted from the central orifices? 



The author next shows that the upheavalists have no correct idea 

 of the mode of formation of craters, which are not formed, as they 

 assert, at one blow, by a single explosion, like the bursting of a bub- 

 ble, or of a mine of gunpowder, but by the repetition of explosions 

 or flashings of steam from the surface of ebullient lava within the 

 volcanic vent (like those of a colossal Perkins's steam-mortar), con- 



