Tertiary Formations. 57 



that they unite in such a way as to form continuous layers, or 

 even to constitute the whole mass. The Pampean formation 

 exhibits no distinct stratification; no division into different 

 beds can be remarked ; it is in fact only one single bed. It 

 is true there are in certain places portions more or less hard, 

 more or less arenaceous ; but these portions, far from being 

 limited by horizontal lines, as we always see in beds tranquilly 

 deposited from water, form a mass in which indistinct zones 

 only can be distinguished, zones which cannot be followed for 

 any distance in any of the natural sections of the falaiaes. 



The earthy mass of the Pampean formation, with its calca- 

 reous nodules, reminds us of the loss of the banks of the Rhine, 

 the limon of the plateaus of Picardy, and the analogous depo- 

 sits observable at some points in the environs of Paris, It is 

 one of the best characterized and best developed examples of 

 those unstratified sedimentary deposits which geologists, fol- 

 lowing the example of M. d'Omalius d'Halloy, now term 

 Limon.'^ It is in this sense that M. d'Orbigny has adopted 

 the denomination of Limon Pampeen, which seems to us pre- 

 ferable to that of Pampean clay {Argile Pampeene) which he 

 had previously employed. The term Tosca, used in the coun- 

 try itself, might have been introduced into science, had it not 

 been already appropriated to designate a deposit of a difi^e- 

 rent composition in the Canary Islands. 



The absence of true stratification induces M. d'Orbigny to 

 suppose that the Pampean loam was deposited in a very short 

 space of time, in consequence of a great movement of water. 

 The only fossils found in it are bones of mammifera, which 

 are sometimes very numerous, and of which the largest and 

 the most remarkable belong to large Pachydermata and to 

 gigantic Edentata, accompanied by some Rodentia and a small 

 number of Carnivora. The Pampean loam or tosca forms the 

 uniform surface of the great basin of the Pampas, rising gra- 

 dually from the level of the ocean, towards the north and west, 



* The following is the definition given by M. d'Omalius d'Halloy : — " Limon 

 is an argillaceous earth, which is rarely suflficiently pure to be regarded as a true 

 clay. It occurs chiefly in plains and in low valleys." — Elements de Gtologiey 1835. 

 —Edit. 



