388 Geological Socicti/. 



beration produced when it is struck sharply, to the cellular nature of 

 the beds of indurated clay which form this floor, and have been de- 

 posited from the washings of the surrounding slopes, and hardened 

 by the influence of heat and moisture. 



The author accounts for the production of two varieties of Piso- 

 lite, which occur in the tufa and decomposed lava of the Solfatara. 

 This hill is recorded to have been in eruption in A. D. 1180 ; and 

 the present crater may have been formed at that late epoch. The 

 hill which supports the Camaldoli, 1613 feet above the sea, is a re- 

 markable mass of indurated tufa ; from beneath which, on the N. E. 

 side, crops out a bed of gray-stone, in which a singular concretion- 

 ary separation has taken place, of the augitic from the felspathose 

 parts; the former appearing as lenticular patches in a base consist- 

 ing of the latter. This and other somewhat similar lavas in the 

 same neighbourhood, give rise to important inferences as to the 

 condition of such substances at the period of their emission from the 

 earth. The solid tufa of Capo di Monte and other hills envelops 

 shells of the same species with those which at present inhabit the 

 Bay of Naples. It is likewise in some points traversed by vertical 

 veins of a finer and harder matter, seeming to have exuded from 

 the sides of a fissure formed in the rock, before it was completely 

 desiccated. 



The author attributes the formation of all these volcanic hills to 

 successive eruptions from below the surface of the sea, though on 

 a shallow shore : and, from the existence of loose tufa over the 

 whole plane of the Campagna, and even to some distance up its prin- 

 cipal valleys, he infers that the sea once washed the foot of the 

 Appenines behind Capua ; and that this plain has since suffered an 

 elevation of 200 feet at least, — an elevation in which the wliole 

 western coast of Italy and the Appenines probably shared ; as ap- 

 pears from the traces of lithophagi in the cliffs between Rome and 

 Palermo, much above the present sea-level, and from other colla- 

 teral testimony. 



March 16. — A paper was read " On the geology of the vicinity 

 of Pulborough, Sussex;" by P. J. Martin, Esq. 



The author's object is to give a detailed account of the district 

 on the north of the South Downs, extending from about Petworth 

 on the west, to Steyning and the Adur on the east, and inter- 

 vening between the portions of Sussex described by Mr. Mantell 

 and Mr. Murchison. The structure of this tract agrees in general 

 with part of the adjoining district on the west; but two of the for- 

 mations are here subdivided into natural groups, which the author 

 conceives ought to be distinguished ; the following being the series in 

 a descending order, that has come under his observation : — 1 . Chalk. 

 2. Firestone, — including upper greensand and Malm-rock. 3. Gal/. 

 4. Shankliii sand, — including, as subdivisions, ferruginous sand, and 

 lower greensand and sandstone. 5. Weald cUuj. 



The portion of tlie Firestone, which the author denominates Up- 

 per Greensand, may be traced distinctly as a thin bed at the foot of 

 the chalk hills from Sutton to Washington, and is best exposed at 

 the entrance of the Arundel defile, resting upon the Malm-rock, — an 



arsjiliaccous 



