2/6 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [DeC. 13, 



of the scaglia-like and impure limestone which here underlies the great 

 mass of macigno. 



Passing from these difficulties, in defining the equivalents of 

 the cretaceous rocks in Liguria, Modena, Lucca and Tuscany, and 

 their relations to inferior and superior strata, the true cretaceous 

 system is not only observable at intervals in the southward range of 

 the Apennines, but on various parallels resumes its calcareous and 

 fossil characters, and constitutes ridges of considerable length in 

 Southern Italy. In the Papal States these limestones, undergoing 

 many undulations and breaks, constitute the chief chains which flank 

 the valleys of Umbria, the Sabine mountains (Tivoli, Subiaco and 

 Palestrina), and the Volscian hills extending to Gaeta and Naples. 

 Although these rocks are in their upper portion chiefly characterized 

 by hippurites, I am unprepared to define to what extent they may 

 be divided into formations representing the neocomian or lower 

 greensand, as separated from the upper greensand and chalk. I will, 

 however, presently describe how these hippuritic limestones of the 

 Sabine hills are surmounted by nummulitic rocks and macigno. In 

 the limestones of Gaeta, whether crystalline, saccharoid or compact, 

 I found many hippurites. The same rocks rising up into the ridge of 

 Monte Marzo, near St. Agata, are underlaid by a thin-bedded, earthy 

 and sometimes bituminous, dark-coloured limestone, which may be 

 considered neocomian. The Jurassic limestones of Sorrento are of 

 great thickness and contain hippurites ; whilst the whole of the above 

 series dips under macigno. 



On the Eoceiie Rocks of Italy and their relations. 



The group of this age, as clearly indicated by its overlying rela- 

 tions to true cretaceous rocks, has been sufficiently described in 

 respect to the Venetian Alps, the Vicentine and Euganean hills. It 

 is also so well known in the environs of Nice, that it is sufficient to 

 cite the memoirs in which it has been noticed*. The great change 

 in mineral aspect which these deposits undergo, as they pass from 



* I visited Nice in 1828 in company with Sir C. Lyell, since which period 

 much progress has been made in our acquaintance with the succession of the 

 strata in its environs. I have, however, a sufficient recollection of the physical 

 relations of the rock-masses to understand the value of the descriptions of the 

 Marquis Pareto (Liguria Marittima), and of M. Perez. The latter gave a very 

 elaborate account of the nummulitic deposits of that tract at the Genoa meeting 

 of the Scienziati Italiani ; but whilst he allowed that the greater pi.it of the 

 numrauUtic fossils were eocene, still, in compliance with the prevailing fashion, 

 he classed them as cretaceous, as well as the adjacent macigno of the Maritime 

 Alps which overlies the nummuhtic group. The sections are, in a general sense, 

 so in accordance with my own in the Alps and Apennines, that it is unnecessary 

 I should do more than say, that they exhibit a succession of various bands contain- 

 ing nummulites, ostreae, &c., the lowest of which repose on beds (often a green- 

 sand) with inocerami of the chalk, and which in other places are charged with other 

 types of the upper cretaceous groups. A Hmestone with neocomian fossils, and 

 another with Oxfordian Jurassic fossils, in descending order, completes therefore the 

 analogy with the succession in the Venetian Alps. The conclusion of M. Perez is, 

 that the macigno of the Maritime Alps is everywhere more recent than the num- 

 mulitic lin^estone* 



