Maack.] 426 [June 1, 



never have been the result of a cataclysm, but that it has been pro- 

 duced in the ordinary way, and that afterwards they were imbedded 

 in the sediment of the rivers. 



To arrive at a true and natural explanation of the origin of this 

 very extensive formation, we have only to study the different causes 

 which are now at work upon the configuration of the continent, 

 namely, river-action and volcanic forces. 



Below this pampa mud we find an extensive formation, the marine 

 character of which is proved by the different remains of sea-animals 

 which are found in it, namely, marine shells, Echinoderms, Crusta- 

 ceans and marine fishes. The diluvium covers the greater part of 

 the Republic, but in consequence of a want of natural sections and 

 cuts, satisfactory exposures are rarely to be found. This formation 

 belongs to the Tertiary period and consists of two divisions. The 

 lower is called, by Alcide D'Orbigny, the " Systeme guaranien," and 

 the upper, the " Systeme patagonien." 



The former corresponds to the European lignite formation, and is 

 developed, particularly on the eastern side of the Rio Parana, com- 

 mencing in the Missiones and extending southward to the mouth of 

 the river Corrientes. This formation consists, in the lower part, of 

 red, ferruginous sandstone which is covered with a ferruginous lime- 

 stone, over which layers of gypseous clay are found. These three 

 parts contain no fossils and belong to the same epoch. In the Uru- 

 guay Republic, near the city Mercedes, on the Rio Negro, I had an 

 opportunity of studying the southern end of this formation, which is 

 very well developed at that place: I searched several days for fossils, 

 but could find none. In the Brazilian province of Rio Grande do 

 Sul, on the Rio Jacuy, lignite is found in this formation, for which 

 reason it must be compared with the European lignite-formation. 



The geognostical and paleontological character of the upper terti- 

 ary formation (Systeme patagonien) is very different from that of the 

 lower division. This formation is also very well developed on the 

 eastern side of the Parana, and especially in the neighborhood of the 

 city of Parana. We find it also in the Uruguay Republic, near Viv- 

 oras, on the Rio Uruguay, as indicated by the presence of shells 

 typical of this division, namely, Venus Miinsteri and Ostrea patagon- 

 ica. In comparison with European sediments this division belongs 

 to the Molasse formation. 



The extent of the tertiary formation over the La Plata States can- 

 not be determined at present for want of sections; but in boring an 



