50 Geology of Bouth America. 



greatest analogy, Now, although we may retain some doubts 

 as to the exactitude of the identification of these different 

 formations considered individually, it seems difficult to avoid 

 regarding it as certain that the palaeozoic system of South 

 America corresponds as a whole with that of Europe, and that 

 it is subdivided in an analogous manner. This great fact, 

 which has been completely demonstrated by M. d'Orbigny, 

 appears to us to be one of the most important with which 

 geology has been enriched of late years. 



Triassic System. — Succeeding the palaeozoic formations, 

 and immediately above the carboniferous sandstones of M. 

 d'Orbigny, there is in South America a system of beds which 

 he refers to the Trias of Europe, and which Mr Pentland* 

 likewise considers as its representative. This identification 

 we regard as indicated with plausibility by the observations 

 made, but still not so rigorously established as that of the pa- 

 laeozoic system. 



The presumed triassic deposits of Bolivia are composed of 

 an alternation of magnesian limestones, of variegated clays, 

 and of friable argillaceous sandstones. The lowest beds con- 

 sist of a magnesian compact limestone, which is frequently 

 divided into very thin waved laminae. M. d'Orbigny has seen 

 this member of the formation, having but a small thickness, 

 near Laguillos, and in the valley of Miraflor. Above these 

 limestones there lie, at the same localities, laminated rose- 

 coloured or variegated clays, which often abound in crystals 

 of gypsum. Above the clays, in the valley of Miraflor, there 

 are compact magnesian limestones, in which M. d'Orbigny 

 discovered numerous fossils, but unfortunately he is unable to 

 particularize more than one species, the others having been 

 lost. This species, the Chemnitzia potonensis, belongs to a 

 new genus of turreted shells, which approaches the Melanias. 



The rocks mentioned above are very analogous to those 

 which constitute the trias group in Europe. The limestones 

 of the Muschelkalk, in the north-east of France, and in the 

 department of the Var, as well as the gres biyarres of the 



* It is much to be regretted that Mr Pentland has not yet published the 

 valuable results of his extensive scientific investigations in South America. — 

 Edit. 



