52 Geology of South America. 



west, and the south of the continent which then existed in 

 those latitudes. The identity of the fossils of the chalk for- 

 mation with those of the same formation in Europe, is not so 

 great as regards the south of the American continent as it is 

 in respect to the north, a circumstance which of course indi- 

 cates a less direct communication. Perhaps we may infer the 

 existence of some long piece of land, which continued as far 

 as America the separation existing in Europe between the 

 Parisian basin and the basin of the Mediterranean. 



Tertiary System. — Another geological fact, and it is one of 

 the most remarkable, is the immense extent of the Tertiary 

 system in South America. When we compare it with the 

 small basins disseminated throughout Europe, we are led to 

 believe, along with M. d'Orbigny, that the smallness of the 

 latter is an exception. The tertiary basin of the Pampas ter- 

 minates and sinks under the Atlantic ocean, from the mouth 

 of La Plata to the Straits of Magellan. Proceeding to the 

 north from this last point, its limits, more or less remote 

 from the Cordilleras, are still uncertain ; but every thing 

 leads us to believe, that the deposit of this epoch occupies the 

 plains to the very base of the lateral chains. Advancing still 

 farther to the north, the tertiary basin of the Pampas extends 

 to the foot of the primitive hills of the province of Chiquitos ; 

 and it even appears that it is prolonged on all sides without 

 interruption through these hills, into the great basin of the 

 Amazon. Regarding only the portion situated to the south of 

 the primitive hills of Chiquitos, the tertiary basin of the Pam- 

 pas extends in the direction of the meridian, from the 17th 

 to the 52d degree of south latitude, over a distance of up- 

 wards of 2400 miles. Its greatest breadth is about 800 miles. 



Throughout this vast extent, and even at the foot of the 

 northern declivity of the hills of Chiquitos, M. d'Orbigny has 

 distinguished, in the American tertiary deposit, three different 

 series, belonging to three successive epochs, viz. 1. The lower 

 beds, destitute of organic remains, which he designates by the 

 name of the Guaranian Tertiary Formation ; 2. A middle 

 portion, evidently marine, containing shells belonging to ex- 

 tinct species, and which he calls the Patagonian Tertiary For- 

 mation : and, 3. An upper portion, containing only skeletons 



