1856.] SCROPE — CRATERS AND LAVAS. 329 



induced to think he over-rates; — I mean the excavating power of the 

 sea iQ forming what he calls " craters of denudation." This phrase, 

 I thiak, he first employed in a paper on the subject read before this 

 Society in December 1849. It is not repeated in the latest edition 

 of his " Principles," and I imagine, therefore, that he is no longer 

 desirous of maintaining its propriety. 



I by no means doubt, that in the case of craters formed beneath 

 the sea, or in such close vicinity to it as to allow its waves and cur- 

 rents to enter and sweep round their interiors, these circumstances 

 must have considerably modified the result. In the former case, 

 that of subaqueous eruption, the resistance of the water above the 

 vent would probably tend to throw off the ejected materials over a 

 wider area. And thus, perhaps, we may account for the vast hori- 

 zontal dimensions of the great crateriform basins of Italy, — Bolsena, 

 Bracciano, Albano, and others, evidently of submarine origin. In 

 the latter case, that of subaerial craters to which the sea has had 

 access through some lateral opening, no doubt great degradation of 

 their internal slopes and cliffs, as well as of the outside, will have 

 often taken place. Many, indeed, will have had their enclosure re- 

 duced to a mere skeleton, like Santorin. Some, like Graham's Isle, 

 have been entirely swept away. But the question being as to the 

 origin of these crateriform hollows, not as to the cause of any sub- 

 sequent alteration of figure, this, I believe, may in every instance, 

 without exception, be most reasonably referred to volcanic explosive 

 eruptions. And, therefore, the employment of such a phrase as 

 "craters of denudation," in contradistinction to "craters of erup- 

 tion," can only lead to a wrong conception of the originating forces. 



Where, indeed, is to be found a crater, the formation of which 

 cannot be accounted for (making allowance for the subsequent modi- 

 fications already referred to) by eruptive phaenomena of the same 

 character as those which have before the eyes of trustworthy ob- 

 servers repeatedly drilled enormous craters through the axis of the 

 cone of Vesuvius ? 



Is it the vast size of some craters which should render such an 

 origin incredible in their instances ? For example, — of the Val di Bue 

 on the flank of Etna, the Caldera of Teneriffe, that of Palma, San- 

 torini, or the external crater of Barren Island j which measure some 

 three, five, or even six miles in diameter ? But the crater of Vesu- 

 vius, formed in 1822, before my eyes, by explosions lasting twenty 

 days, measured a mile in diameter, and was more than a thousand 

 feet deep. The old crater of Somma, which half encircles the cone 

 of Vesuvius, is about three times as wide as the crater of 1822. Are 

 we, then, on that account alone, to believe that it could not have 

 been produced by an eruption of proportionately greater violence, — 

 when, too, such an eruption is known to have occurred about the 

 time this crater must have been formed, namely in the year 79, and 

 to have overwhelmed three cities at the base of the mountain be- 

 neath its enormous fragmentary ejections ? Is it not, on the con- 

 trary, much more in accordance with sound philosophy to ascribe 

 the excavation of the old concentric crater of Somma to the same 



