PROCEEDINGS 



OF 



THE GEOLOGICAL SOCIETY OF LONDON. 



1827. No. 2. 



March 2. — Henry Blanshard, Esq. of Great Ormond Street, Lon- 

 don ; Richard Cowling Taylor, Esq. of Wilmington Square, London ; 

 and John Watson Pringle, Esq., Captain in the Royal Engineers, — 

 were elected Fellows of the Society. 



A paper was read, " On the volcanic district of Naples;" by G. 

 Poulett Scrope, Esq. F.G.S. F.R.S. 



In this paper the author purposes to confine himself to a general view 

 of the volcanic formation of this district, and to such observations as 

 have hitherto escaped notice, or on which he differs from other writers. 



At one extremity of the tract in question lies the habitually erup- 

 tive volcano of Somma; at the other the once active vent of Ischia ; 

 the intermediate space is studded with hills, evidently thrown up by 

 numerous eruptions, succeeding one another at distant intervals, 

 and from separate though neighbouring orifices. These are arranged 

 in one general band, which is remarkable from its parallelism to the 

 elevated limestone range forming the opposite side of the Bay of 

 Naples, and separating it from that of Salerno. 



Sorama is a very regular, volcanic mountain, created by the accu- 

 mulation of repeated streams of basaltic lava and beds of ejected 

 ashes, sand and scoria, round a central and habitual vent. 



The author dissents from the theory of Von Buch, that such 

 mountains were produced by the forcible elevation of horizontal 

 beds round an aperture of eruption ; — though he allows that beds 

 originally inclined, may often suffer a certain degree of elevation, 

 during the shocks occasioned by the forcible protrusion of lavas 

 from below, into the fissures through which they are emitted. 



The great crater of Somma is attributed to the explosions of the 

 "paroxysmal eruption" of A. D. 79 j and the whole cone of Ve- 

 suvius which occupies the centre of that crater, is stated to have 

 been created by repeated, subsequent eruptions. This cone is si- 

 milar in structure to that of Somma, as is seen in the walls of its 

 actual crater, compared with those of the Atrio del Cavallo. 



Ischia is a less regular, volcanic mountain ; has produced no leu- 

 cite, and none but trachytic, or rather, according to the author's 

 nomenclature, gray-stone lavas, — a class intermediate between tra- 

 chyte and basalt, and consisting of felspar and augite. The great 

 mass of the island is composed of the conglomerates belonging to 

 this class of lavas, forming an indurated tufa of a light green colour. 

 There are traces of a vast central crater on the west of the Monte 



