48 Geology of South America, 



limestone occupies but a very limited space, and the first 

 points, advancing to the east, where the carboniferous forma- 

 tion acquires any development, are on the great Bolivian 

 plateau. M. d'Orbigny there observed several chains of it, 

 such as the Apocheta de la Paz, the hills of Aja, and of 

 Aygachi de las Penas, all the islands of Quebaya and of Pe- 

 riti in the lake of Titicaca, and more to the south the hills of 

 Guallamarca and of Pucara, and some other patches. In 

 general, the carboniferous strata are distributed chiefly to 

 the east and to the west of the great Bolivian system, where 

 they attain, especially to the east, an elevation of more than 

 13,000 feet. The carboniferous formation likewise forms, in 

 the Chiquitian system, summits whose height is sometimes 

 nearly 5000 feet, both in several chains of that system in the 

 east and north of the provin 3e, and also more to the east in 

 the province of Minas-Geraes. 



The different beds united by M. d'Orbigny under the de- 

 nomination of the carboniferous system are nevertheless divided, 

 as I have already said, into two distinct series, the one con- 

 sisting chiefly of limestones, and the other of sandstones ; the 

 first being the lower and fossiliferous, the last the upper and 

 without fossils ; and these two series, which occur united on 

 the great Bolivian plateau, are elsewhere separated, for M. 

 d'Orbigny found only the upper reddish sandstones, and never 

 the limestones, to the east of the plateau, and on the Chiqui- 

 tian system. There is therefore an important diff*erence in posi- 

 tion between these two series of beds. This difl^erence might 

 induce us to doubt whether the upper series is really to be 

 regarded as belonging to the carboniferous system, and might 

 lead us to refer it with as much probability to some one of 

 the systems which succeed the carboniferous group in Europe, 

 for example, to the red sandstone. The lower series is in fact 

 the only one which can with great probability be referred to 

 the carboniferous system. It is indeed only in the limestones, 

 and in the calcareous sandstones of the inferior series, that 

 M. d'Orbigny has found fossil organic bodies. He met with 

 them at Yarbichambi, and in the islands of Quebaya and 

 Periti, in the lake of Titicaca. The shells are in an excel- 

 lent state of preservation, and retain all the necessary zoolo- 

 gical characters. 



