Maack.] 424 [June 1, 



marl mixed with clay and lime, and more or less sand. This Tosca 

 is found especially near the coast of Buenos Ayres, where it forms 

 large rocks which may be easily examined at low tide. The first 

 impression is more that of a dissolved granitic rock; but a more 

 careful examination shows that it is only a mechanical composition 

 of clay and lime, containing some fine grains of quartz, and not at all 

 a crystalized mass which could have been formed in a regular chem- 

 ical way out of the diluvial sediment. 



Just as these Tosca concretions are found only in a comparatively 

 very small area of the Diluvium, so pebble stones are found in this 

 pampean mud only at certain localities, namely, near the interior 

 chains of mountains, especially those of Cordova. 



More frequent and extensive than these two last peculiarities of 

 the pampean formation are the " Lagunas" that is to say, lakes of 

 salt water, which give to the whole country a peculiar character. 

 They are always situated in the low lands, and their bottom con- 

 sists of that impenetrable, red, pampean clay. They extend over a 

 very large area, from the 23d degree of south latitude near 

 the Rio Vermejo, to the 50th degree, but differ in this respect, 

 that in the northwestern part the lagunas are more or less dry on 

 account of the want of rain, while in the southern and eastern parts 

 they are filled with water during the whole year. The fall of 

 rain in these regions is nearly four times greater than that of the 

 northwest. Salinas is the name given to the dry lagunas; but those 

 larger plains in the south which, at the dry season are covered with 

 an efflorescence of salt, are called " Salitrates." The Spaniards called 

 this saline crust " SaUti-ates" because they believed that it consists 

 of saltpetre; but this is not so; it is composed of Glauber's salt (XaO, 

 SO 3 ) and gypsum (CaO, SO 3 ). These deposits are found especially 

 near Bahia Blanca, and only at those places which lie but a few feet 

 above the level of the ocean. At the southern Colony, " El Carmen 

 cle Patagunes" near the Rio Negro, there exists a very large salina 

 consisting almost entirely of common salt (Na CI) . <tfbi earlier years 

 it was collected as an article of commerce, but it is too pure for 

 this purpose; the want of other saline elements rendering it useless 

 for salting meat. In Brazil and Uruguay, where the underlying rocks 

 are of a granitic structure, these salinas are never found. In order 

 to explain this curious phenomenon we must suppose that the great- 

 est part of the Argentine Republic was covered at an earlier period 

 by the ocean, and after its recession, these saline lagunas remained 



