1850.] ZIGNO ON THE VENETIAN ALPS. 427 



all the vast calcareous region of the Sette Comuni and that which 

 extends from the left bank of the Brenta to Belluno and Friuli, this 

 well-marked horizon may be traced. Even in the group of Euganean 

 Hills, which rise like an island in the plain at a distance of thirty miles 

 from the chain, in the midst of the confusion produced by the tra- 

 chytes and basalts, I have recognized the Jurassic formation by the 

 presence of this ammonite limestone abounding in fossils. These 

 prove its synchronism with the Oxford clay and coral rag of England, 

 and cannot be confounded with those of the other red limestones of 

 Italy which have been referred to the lias. 

 The following are very abundant : — 



A.mmonites anceps, Ziet. Ammonites Tatricus, Pusch. 



athleta, PMll. Cidaris coronata, Goldf. 



viator, D^Orb. Glypticus hieroglyphicus, Agass. 



Hommairei, D^Orb. Ananchytes bicordata, Lamk. 



Zignodianus, DWrb. 



And in the upper beds, Atnmonites perannatus, Sow., and^. bipleoOy 

 Sow., several Aptychi of the family Lamellosi, and lastly Terebratula 

 diphya, Buch, and a Terebratula allied to T. triangularis, Nilss. 



Hence it would appear that the upper beds of the ammonite Hme- 

 stone which are the most argillaceous represent the upper Jurassic. 

 Above the ammonite limestone and conformable to it, as may be seen 

 both on the plateau and on the southern flank of the chain, appear 

 the different groups of the cretaceous system. 



Hitherto Italian geologists had included aU its strata under the 

 name of Scaglia, which they conceived to represent the upper creta- 

 ceous beds, while some of them looked on the ammonite limestone as 

 the representative of the lower greensand. M. von Buch, at the 

 meeting of Italian naturalists at Milan in 1844, showed that the am- 

 monite limestone belonged to the oolites ; and the fossils I have since 

 discovered in it enable me to place it in the Oxfordian group. In 

 like manner by fossils I have been enabled to distinguish incontesta- 

 bly the different cretaceous beds which lie upon it, the lowest of which 

 is a white or sometimes greyish limestone with a conchoidal fracture, 

 which we call Biancone. Its perfect conformability with the upper 

 beds of the ammonite limestone on which it is seen to repose, had 

 caused geologists unacquainted with its fossils to classify it with the 

 upper oolites ; while others, founding their conclusions on mineralo- 

 gical characters, confounded it with certain beds of the scaglia, which 

 though thinner strongly resemble the biancone, and can only be di- 

 stinguished from it by fossils. 



It was in the biancone of Mont Vignola among the Euganean Hills 

 that I first found specimens of Crioceras, and especially the Crioceras 

 Emmerici, Le'v., which is characteristic of the lower Neocomian beds. 

 This made me suspect that this rock was our representative of the 

 Neocomian system, and I lost no time in satisfying myself of this by 

 studying the biancone fossils collected by myself, as well as those of 

 the museums of M. da Rio, of M. Parolini, and of the University and 

 the Seminary of Padua. After careful researches I have procured 

 from the biancone of the Euganean Hills, in the neighbourhood of 



VOL. VI. PART I. 2 H 



