272 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [DcC. 13, 



great columns in the fa9ade of St. Peter are made, as well as the 

 "breccia di Simone," are the Roman representatives of the "ammo- 

 nitico rosso," or Oxfordian. 



Of the extent to which Jurassic rocks may crop out on various 

 parallels of the grand mountainous undulating region of the central 

 Apennines, which runs down from the lofty Sibilla and Leonessa into 

 the kingdom of Naples, no one is yet perfectly informed ; but the 

 researches of Orsini and Alessandro Spada teach us that Jurassic rocks 

 reoccur on the eastern side of the axis, the chief elevated points of 

 which are either cretaceous or nummulitic. I satisfied myself, indeed, 

 that the mass of mountains coloured as Jurassic by CoUegno, which 

 extends from Civita Castellana to Gaeta, is cretaceous, and forms part 

 of the rocks of that age around Naples * . The lowest visible strata, 

 however, in the great promontory on the south side of the bay of 

 Naples, and notably the bituminous limestones of Torre Orlando, 

 are classed by Agassiz as Jurassic because they contain the Pycnodus 

 rhombus, Ag., Notagogus Pentlandi, Ag., &c. Again, certain lower 

 strata of the Val Giffoni, east of Nocera, may be referred to the age 

 of the lias, in consequence of the description of their ichthyolites by 

 Sir P. Egerton, viz. the Semionotus Pentlandi (Egert.), S. pustu- 

 lifer (Egert.), and S.minutus (Egert.) f. 



Cretaceous Rocks of Italy. 



Clear distinctions between the cretaceous and Jurassic rocks of 

 Italy can, for reasons already assigned, be seldom safely effected, ex- 

 cept where the one or the other contains fossils, and can thus be com- 

 pared with the types in the Alps. At Nice on the west, near Milan 

 in the centre, and in the Vicentine on the east, the flanks of the Alps 

 afford us, indeed, good keys, which explain the order of succession. 

 But we no sooner quit the edges of those mountains and advance into 

 Italy, than we lose for a long space nearly all evidences of true cre- 

 taceous rocks as proved by their fossils. We then find ourselves in 

 broad, mountainous undulations of sandstone, schist, and impure lime- 

 stone, some of which have a striking resemblance to the flysch of the 

 Alps. The geological map of Liguria Marittima, by the Marquis 

 Pareto, extending from Nice on the one hand to La Spezia on the 

 other, and the work that accompanies it|:, expose the difficulties, 

 which even an able geologist intimately acquainted with his country 



* The author of this map is aware of the error, and informed me of it before I 

 visited the tract. In the first effort to map a country such errata are inevitable, 

 and our best thanks are due to M. Collegno for his endeavour to produce the first 

 general geological map of his country. 



f See Proc. Geol. Soc. Lond. vol.iv. p. 183. 



X In the * Cenni geologici sulla Liguria Marittima,' p. 30-47, Pareto considers 

 all the macigno and alberese of Liguria to be cretaceous or secondary, because 

 it contains fucoids. It is nowhere associated with nummulites. But in respect 

 even to the latter, he classes the lowest great band of them at Nice as also cre- 

 taceous, because it succeeds in overlying order to a representative of the chalk in 

 which green grains abound. In truth, however, there can be no doubt that all the 

 nummulite rock of Nice is truly eocene and tertiary, and that it reposes on the 

 equivalent of the chalk with inocerami. As to the non-fossiliferous macigno and 

 alberese of the Genovesato, it is hopeless at present to define their age with pre- 



