1859.] SCROPE CONES AND CRATEES. 505 



posterior margins of the orbits, enclosing between them a tabulated 

 sm-face, which, occup^dng the central and most elevated parts of the 

 general surface, forms a prominent feature. The orbits are small 

 and slightly oval ; they are situated entii-ely on the antenor half of 

 the shield. The enamel-layer forms small, oblong or round, pearly 

 drop-like tubercles, which are numerous and for the most part 

 chscretc. The spaces between them are grooved into parallel or 

 slightly divergent ridges, which pass from their sides and ends. The 

 structiu'e of these tubercles is very vascular. 



Associated with this fossil, the author foimd the dermal plate or 

 the tooth of a placoid fish, which has close resemblance to the teeth 

 of Cestracion and the Eays, and even closer still with the bone of 

 the Siliman bodies called by Pander Coelohjndce. It was discovered 

 almost between the jaws of C. Sahveyi, and thus suggests the para- 

 doxical question — does it belong to that fish ? 



Febrtjaey 2, 1859. 



Signer Gennaro Placci, Florence, and Zacatecas, Mexico ; John 

 Henry Sylvester, Esq., Assist.-Surgeon, Indian Army ; and Joseph 

 Frederick AYhiteaves, Esq., St. John Street, Oxford, were elected 

 Fellows. 



The following communication was read : — 



On the Mode o/Forhatiox o/Tolcanic Coxes and Craters. 

 By G. PorLETT Scrope, Esq., M.P., F.P.S., F.G.S., &c. 



Ix a paper read before the Society in April 1856, I called attention 

 to this subject *. I should have thought fiuther reciu-rence to it 

 unnecessary had it not been that, in the first part of the fourth 

 volume of Baron Humboldt's ' Kosmos ' (of which a translation has 

 recently issued from the press, under the superintendence of General 

 Sabine), that distinguished author, while treating very fully of vol- 

 canic action, gives the unquahfied support of his great authority to 

 the theory of upheaval as contradistinguished from that of eruption 

 in reference to the origin of volcanic cones and craters, — a theory 

 which, in common with Sir Charles Lyell, M. Constant Prevost, and 

 many others, I believe to be not merely erroneous, but destnictive 

 of all clearness of apprehension as to the part which volcanic action 

 has really played in the structural arrangement of the earth's 

 siu'face. 



I think I shall be justified in this last observation in the opinion 

 of any person who will penise wdth attention Baron Humboldt's work, 

 and endeavour to realize some definite idea of what the author con- 

 siders volcanic action to be — ^how cones or craters are formed — how 



* Quart. Journ. Geol. Soc. vol. xii. p. 326. 



