46 Geology of South America. 



of Cuyaba, mountains which follow the same direction as those 

 of Chiquitos, and which, according to M. d'Orbigny, belong 

 to the same system. Perhaps, he adds, the same rocks are to 

 be found more to the east, in the province of Minas-Geraes, 

 a supposition which seems to be confirmed by the meritorious 

 labours" of M. Pissio, which were lately laid before the Aca- 

 demy of Sciences. 



MM. Humboldt and Eschwege have, for a long time, 

 fixed the attention of observers on the rocks of stratified 

 quartz which occupy vast areas in South America, to the 

 south of the Equator, in Peru as well as in Brazil.* These 

 stratified quartzes were divided among various primitive and 

 secondary formations ; perhaps a judicious application of the 

 principle of metamorphism, such as was lately suggested by the 

 memoir of M. Pissio,f may enable us to include all under one 

 and the same formation, the Devonian formation of M. d'Or- 

 bigny. The exact determination of the age of the quartzose 

 sandstones of Bolivia is thus an important question for the 

 geology of South America, and even, we may say, of the 

 greater part of the Southern Hemisphere, if, as we may pre- 

 sume, the quartzose sandstones of Table Mountain, near the 

 Cape of Good Hope, belong to the same formation. 



In the Devonian formation of the province of Chiquitos, M. 

 d'Orbigny did not observe a single trace of fossils ; whereas 

 he observed fossils several times in the lower parts of the 

 sandstones of the same system in Bolivia, especially at Acha- 

 cache, near the lake of Titicaca, in the environs of Cocha- 

 bamba, near Totora, and at Challuani, in the province of 

 Mizque, in the provinces of Tocopaya and Yamparaes, in the 

 department of Chuquisaca. These fossils, which belong to 

 the genera Spirifer, Orthis, and Terehratula, are always in 

 the state of impressions, and occur in widely extending but 

 very thin layers, between the laminae of the rocks. Of seven 

 species of these difi*erent genera which M. d'Orbigny brought 

 from Bolivia, four have the greatest resemblance to fossils 

 of the Devonian system of Europe. Some of the others ap- 



* Humboldt, Essai geognostique sur le gisement des roches dans les deux 

 hemispheres, p. 91, 9G. 



t Comptes Rendus, vol. xvii., p. 34. Meeting of 3d July 1843. 



