1848.] 



MURCHISON ON THE STRUCTURE OF THE ALPS. 



275 



the vast masses of associated macigno sandstone are scarcely more pro- 

 ductive. As to the fucoids found in the Florentine Apennines, they 

 have much too great a vertical range to aiford any criterion whatever 

 of the true age of the rocks. Forms said to be similar occur in the 

 grey or lower scaglia of the Venetian Alps, and are, as I have shown, 

 still more abundantly developed in the supracretaceous macigno or 

 flysch of the Northern Alps. 



Rare as they are, certain fossils have, however, been found ; and the 

 existence of the solitary Hamites Micheli of Fiesole, of one ammonite 

 discovered by Mr. Pentland, and of another by the Marchese Pareto, 

 are, in the absence of other countervailing fossil proofs, enough to 

 satisfy me, that there is here a zone, which, in a peculiar lithological 

 form, represents the cretaceous system, as on the north flank of the 

 Carpathians. I consider this group to be the equivalent of the upper 

 greensand and chalk, which has assumed very much the same "flysch" 

 or macigno characters as the cretaceous deposits of Gosau. I am very 

 far, however, from agreeing with Professor Savi, that all the macigno 

 is cretaceous. On the contrary, I am convinced that probably the 

 largest masses of that rock, and particularly whenever they surmount 

 or are associated with nummulitic strata, are of eocene age. The 

 beds at Perolla, near Massa Marittima, which contain the Gryphsea 

 figured by Pilla, represent in my estimate the uppermost cretaceous, 

 or band of transition into the lower tertiary rocks. 



True equivalents of the neocomian are, as before said, rare in the 

 north of Italy. In the environs of the baths of Lucca, the position 

 and lithological aspect of the mountain called *' Prato Fiorito " led me 

 to believe that it was of neocomian age. It is composed of compact 

 cream-coloured hmestone {a and b, fig. 33), with numerous nodules of 



Fig. 33. 



East of the Baths of Lucca. 



W.N.W. 



Prato Fiorito. 



E.S.E. 



Hard grey and green macigno. 



Alberese. 



Neocomian ? 



flint, precisely resembling the " biancone" which in the Venetian Alps 

 is proved to be of that age. Moreover, I found it to be surmounted 

 by bands of impure sandy limestone, schist, red scaglia, &c. (c and d), 

 which might very well pass for the greensand and chalk ; whilst the 

 great mass of macigno overlying the whole series constituted the chief 

 peaks of the surrounding mountains. These again are followed by a 

 peculiar calcareous breccia and agglomerate (/), which seemed to 

 occupy the usual place of the chief nummulitic zone of Italy ; the whole 

 being surmounted by the great mass of macigno of which the sur- 

 rounding adjacent mountains are for the most part composed. But, 

 after a long search, I could find no organic remains except a rude 

 cast, which might be a Crioceras, and which I detected near the sum- 

 mit of the supposed neocomian. Fucoids indeed are seen on the faces 



