16 GEOLOGICAL MEMOIRS. 



magnesia, is found on the mud. Concretions of iron-stone are some- 

 times found in the sand. Further to the north and east, towards 

 Angostura and Asuncion, the country becomes more hilly. The 

 hills are principally formed of a fine-grained grey sandstone, in hori- 

 zontal beds or with a slight dip to the north : it is sometimes com- 

 pact enough to be used for a building-stone, and quarries have been 

 opened in the hills near Emboscada. The sandstone contains many 

 beds of conglomerate, resembling Nagelfluh. In several places be- 

 tween Asuncion and Villarica, magnetic iron is found in the sand- 

 stone, which has partly passed into oxide of iron and hydrated per- 

 oxide, but still strongly attracts iron-filings : nodules of clay-iron- 

 stone are found in the streams. This sandstone is of tertiary age. 

 Near Asuncion it contains a thick-shelled oyster, resembling Ostrcea 

 canadensis, Lam. Near the same town, bones of fossil Mammalia 

 have been found, which according to Eengger belong to the Mega- 

 therium. They were found at a moderate depth in a sandy loam, 

 which distinctly belongs to the Diluvium and not to the underlying 

 sandstone. 



Higher up the Paraguay, north of Tavego, occurs a fine-grained 

 calcareous sandstone, of a yellow and grey colour, which is used for 

 whetstones. 



Limestone has lately been found on the left bank of the Paraguay, 

 from 25 to 30 leagues north of Villareal ; this is the only spot in 

 Paraguay where it is found in situ. 



Near Itapua on the river Parana there occurs a round lump of 

 calcedony, of a honey-yellow colour, and filled with quartz ; which 

 makes it probable that trap exists to the east of the extensive tertiary 

 formation. Similar fragments of calcedony and quartz are found in 

 the streams of the forest-country, or Montes, opposite to the Sierra 

 de St. Jose. A fragment found near Yhu consisted of a compact 

 granular quartz or quartzose sandstone. Lastly, the streams also 

 bring down little bits of a coarse-grained granite with flesh-coloured 

 felspar. Our traveller * has not reached the range of mountains 

 whence these specimens were derived. 



[J. C. M.] 



* M. Rengger, whose collection of rock-specimens has been presented to the 

 Basle Museum. 



