12 F. AmegJiino — Geology of Argentina. 



The true Patagonian Formation is undoubtedly Eocene, while its 

 basal or inferior part belongs to the Cretaceous. All the malaco- 

 logists (D'Orbigny, Sowerby, Philippi, Hupe, Remond de Corbineau, 

 Steinmann) who have studied the shells of this formation, have 

 assigned it to the Eocene, and some to the Upper Cretaceous. All 

 have recognized that the molluscs, even those of the upper beds, 

 belong entirely to extinct species. The fact is, that the Patagonian 

 Formation begins with the Upper Cretaceous, but acquires its great 

 development during the Eocene. The fossiliferous deposits of 

 Quiriquina were at first regarded as Tertiary, and were only assigned 

 to the Cretaceous after there had been discovered in them remains 

 of Plesiosaurus ( Cimoliosaurus) Chilensis, of Ammonites, and some 

 other Secondary genera. 



The late Cretaceous formation of the coast of Chili exhibits abso- 

 lutely the same aspect and the same lithological characters as the 

 Patagonian Formation. The facies of the fauna is equally the same, 

 since the Cretaceous fauna of Quiriquina only differs from the fauna 

 of the Patagonian Formation by the presence of eight genera 

 (Ammonites, Samites, Baculites, Fugnellus, Cinulia, JPholadomya, 

 Monopleura, Irigonia), which are not met with in this latter ; while 

 85 per cent., more or less, of the genera of the Cretaceous formation 

 are also found in the Eocene Patagonian Formation. Moreover, 

 according to Philippi, the best authority on the subject, 20 per cent, 

 of the species of shells of the Cretaceous formation of Algarrobo are 

 likewise species of the Patagonian Formation, and it will be recog- 

 nized that in Patagonia the marine Cretaceous and Eocene formations 

 pass from one to the other in a gradual and insensible manner. 



At different points on the coast of Chili, the Cretaceous beds are 

 covered by a stratum of lignite, which appears to be the same as 

 that worked at Punta Arenas, and which on this side of the 

 Cordillera extends to the north, below the Patagonian Formation, 

 appearing successively at the source of the Coyle, in the neighbour- 

 hood of Lake Argentina, in the bay of San Julian, in the Eiver Chico, 

 and at other points. 



In the vicinity of Lake Viedma, the lower beds of the Patagonian 

 Formation contain remains of Chondropter3^gian fishes of Cretaceous 

 species or genera, as Lamna (Otodus) Argentina, Amegh., very 

 close to Lamna (Otodus) divaricatus, Leidy, from the Cretaceous 

 of North America; teeth absolutel}' similar to those of Lamna 

 svhnlata, Agass., and Oxyrhina Mantelli, Agass., from the Cretaceous 

 of Europe,' teeth of the Cretaceous genus Sphenodus, etc. These 

 remains are found mingled with those of a genus of reptiles of the 

 group of the Plesiosauria (Poli/ptychodon Patagonicus, Amegh.), and 

 another of the family Mosasauridee (Liodon Argentinus, Amegh.^), 

 both characteristic of the Cretaceous formations. 



Being, then, an indisputable fact that the beds with Pyrotherium 

 are anterior to the base of the Patagonian Formation, it is absolutely 



' F. Ameghino, " Sobre la Presencia de Vertebrados de Aspecto Mesozoico, etc. " : 

 Eevista Jardin Zool. Buenos Aires, vol. i, 1893, p. So. 

 2 F. Ameghino, ibid., pp. 79-83. 



