F. Amegliino — Geology of Argentina. 11 



the ocean, inrlicating that at that epoch the continent extended much 

 more to the east than at any of tlie later periods. 



It is useless to attempt to minimize the clear significance of these 

 facts, saying that the Dinosauria may have lived in Patagonia until 

 a more recent epoch than in other regions of the globe, because the 

 stratigraphical data appear conclusive, and on the other hand the 

 marine fauna leads to absolutely identical results, as is demonstrated 

 by some brief considerations on the Patagonian Formation, which 

 some authors, who are not acquainted with it, attempt to refer to the 

 Miocene, while all who have studied its fauna are agreed in regai-ding 

 it as Eocene.^ If the terrestrial formations of Patagonia pass 

 insensibly from the Cretaceous to the Tertiary, we shall see that 

 exactly the same happens with the marine formations of the same 

 region. 



The Patagonian Formation. 



In the interior of the Territory of Chubut and in northern Pata- 

 gonia, in the upper course of the River Negro and of the Neuquen, 

 the Fyrotherinm Formation is found covered by more modern deposits 

 of terrestrial or fresh-water origin, whose fauna is still unknown to 

 us, except some or other remains referable to the Ancylopoda. In 

 the region of the Atlantic coast, on the contrary, the beds with Fijro- 

 iherium are found below the marine Patagonian Formation. As 

 I have had occasion to point out in another work,^ this is a fact 

 definitely ascertained and beyond all dispute, since the direct super- 

 position of these two formations has been determined by Carlos 

 Ameghino at more than fifty distinct points, very far from one 

 another. 



On the coast the greatest development of the Patagonian Formation 

 is met with to the south of the Eiver Deseado as far as the mouth of 

 the Eiver Santa Cruz, but towards the interior it disappears beneath 

 the thick strata of the Santa Cruz Formation ; to the south of the 

 River Santa Cruz it diminishes gradually in thickness, and disappears 

 beneath the sea before reaching the River Coyle, being replaced in 

 the cliffs by the Santa Cruz Formation. The point of its greatest 

 development is found in San Julian, where it attains a thickness of 

 approximately 300 metres. 



A most important fact, which must not be forgotten for a moment, 

 is that the true Patagonian Formation of the coast of Patagonia is 

 not to be confounded with the marine formations of the neighbour- 

 hood of the Parana. This identification is a grave error which has 

 given rise to many others, since, as I have shown in another work,^ 

 the marine deposits in this latter locality are indisputably more 

 modern than the deposits with Ostrea Fatagonica of the coast of 

 Patagonia. 



\} See supplementary note by the translator, p. 22.] 



^ F. Ameghino, " Premiere Contrib. Conuais. Faune Mammal. Couches a Pyro- 

 therium^' : Bol. Inst. Geogr. Argent., vol. xv, p. 605. 



^ F. Ameghino, "Enumeration Synoptique des Especes de Mammiferes Fossiles 

 des Formations Eocenes de Patagonie," p. 5 (Buenos Aires, 1894). 



