1848.] MURCHISON ON THE STRUCTURE OF THE ALPS. 2/1 



of A. elegans, occur in the mountains east of Perugia, and also in the 

 red marble limestone of Monte Malbe, west of that city. The Am- 

 monites Tatricus and others of the Oxfordian group are found in the 

 limestones of Monte Subasio, east of Assisi, and at La Rossa, between 

 Fossato and Fimbriano. In this region also, as in the Apuan Alps 

 and at La Spezia, such ammonitic rocks rise out as axes, throwing off 

 troughs of younger strata, the sides of the hills being for the most 

 part occupied by vast accumulations of macigno. 



At Cesi, near Terni, on the very outer western edge of the Apen- 

 nine chain, I found red limestone and shale, in parts undistinguishable 

 from the "ammonitico rosso" of the Venetian Alps or that of La 

 Spezia, presenting a bluff escarpment to the tertiary subapennine ac- 

 cumulations of the valley of the Tiber, and loaded with characteristic 

 ammonites, such as Ammonites Tatricus^ A. biplex^ &c. The red 

 ammonitic rocks of Cesi, which are clearly of Oxfordian age, repose 

 upon a grey limestone of perhaps a thousand feet in thickness, with 

 siliceous or flint nodules, and are covered by flaglike limestones and 

 bosses and peaks of dolomite. Now, if characteristic fossils were not 

 found in the red zone (a rare pheenomenon in the Apennines), who 

 could have divined the age of these rocks ? and how should we have 

 seen speculations on the underlying flinty cream-coloured limestone 

 being perchance neocomian or scaglia ? It is indeed a nauseous task 

 for the geologist to wander for days in these mountains without the 

 trace of fossils, and hence the ammonites of Cesi are invaluable land- 

 marks. 



The palaeontological researches of Professor Ponzi in the eastern 

 half of the Papal States, when combined with the mineralogical de- 

 scriptions of his distinguished coadjutor Count Lavinia Medici Spada, 

 in reference to the volcanic and crystalline rocks, will, I trust, at no 

 distant day be embodied in a work which, coupled with the labours of 

 Count A. C. Spada and Prof. Orsini on the Adriatic side of the great 

 axis of the Apennines, will throw much light on this subject. Pro- 

 fessor Ponzi has assured me, that however difficult to separate these 

 limestones lithologically, there are numerous places along the western 

 edge of the chief ridge of the Apennines (extending from Scheggia 

 and Monte Cucco on the N.N.W. by Fossato Gualdo to Col Fiorito 

 on the S.S.E.), where limestones with Jurassic ammonites occur, and 

 that near La Scheggia and elsewhere these are seen to pass under 

 cretaceous rocks. Now, this ridge is parallel to others of similar age : 

 1 st, that of Monte Subasio and its prolongations on the east side of 

 the valley of Spoleto ; 2ndly, of Cesi, west of Terni ; and 3rdly, that 

 of Monte Cetona ; and another might even be enumerated in the 

 Tuscan Maremma. These facts sufficiently indicate the prevalent out- 

 line of ridges and troughs directed from N.N.W. to S.S.E., into which 

 so large a portion of the peninsula is divided. Patient examination, 

 however, can alone detect the extent to which true Jurassic rocks, as 

 defined by the fossils, are separable from those of neocomian and 

 cretaceous age. 



Amidst the varieties of marble which abound in the Roman States, 

 there is little doubt that the common red '' cottannello," of which the 



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