1859.] SCEOPE CONES A^^D CRATERS. 507 



more than thirty years ago I addi^essed to the Society upon the same 

 subject ; and, under these circumstances, I hope I shall not be 

 deemed to trespass unnecessarily upon the attention of its members 

 if I now offer to them some further considerations in opposition to 

 what cannot be yet looked on as an exploded fallacy. 



I shall avoid repeating, and only briefly allude to, the able argu- 

 ments with which all are conversant in Sir Charles Lyell's pubhca- 

 tions, and endeavour to reinforce them by others derived chiefly 

 from my own observations. 



But first it will be convenient that I should clearly point out what 

 is the real question in dispute. 



In common with the unscientific world, and forming their judg- 

 ment on the usual character of the observed phenomena of volcanos, 

 all the early geologists who made this department of science their 

 special study — such as Saussure, Spallanzani, Sir W. Hamilton, 

 Dolomieu, Breislak, &c. — were accustomed to consider a volcanic 

 mountain as the result of the accumulation, over and around an 

 eruptive vent, of the fragmentary matter and lavas thrown out from 

 it. Where but one eruption had occurred, the result appeared to 

 them to be a conical hill composed of scorise, lapilli, or other loose 

 ejecta, usually having a crater at its summit, and a single current 

 of lava, which, after flowing from the summit or flank, or perhaps 

 from the base of the hill, spread over the adjoining surfaces in a 

 sheet or stream, whose dimensions would be determined by the 

 quantity and fluidity of the lava emitted, and by the levels of the 

 surface upon which it was poured out. Where repeated eruptions 

 occurred from the same habitual volcanic vent, the result, it was 

 naturally supposed, would be a proportionately larger and higher 

 cone ; a volcanic mountain, in fact, composed (as such mountains 

 are observed to be) of irregularly alternating layers of fragmentary 

 ejecta and lava-streams, sloping outwardly on all sides from the 

 central summit of the volcano, where the vent would be generally 

 marked by a crater. 



Thus, to give a single instance, Spallanzani describes the island 

 of Saline, one of the Lipari group, as composed of repeated beds of 

 lava and scoriae, one above the other, sloping from the summit-edge 

 of the crater to the sea around ; and goes on to say, " We must con- 

 clude that there were at least as many eruptions from the summit of 

 this mountain as we can count beds of lava. Thus it is that volcanic 

 mountains are for the most part formed. In the beginning it is only 

 the accumulation of the products of one first eruption ; then a 

 second takes place ; then a third ; and the mass goes on increasing 

 always in bulk in proportion to the number of eruptions. Thus was, 

 no doubt, formed, increased, and extended the colossal bulk of 

 Etna. Such was the origin of Vesuvius, of the Lipari Isles, and of 

 other volcanic mountains, — not, however, forgetting that some 

 minor volcanic hills, like the Monte jS^uovo, and the Monte Rosso on 

 the flank of Etna, were produced by a single eruption*." 



For this simple and common-sense theory of the mode of forma- 

 ^ Spallanzani, ' Voyage dans les Deux Siciles,' ii. p. 116. 



