192 
SOUTH AMERICAN GEOLOGY 
have been recorded by Kayser and Steinmann respectively (Obolus, 
Lingulella, Orusia, Eoorthis, Olenus, Conocephalites, etc.). This 
represents the only Cambric terranes known on the continent al¬ 
though there may be an unknown extension of these rocks north¬ 
ward in Bolivia. Some probability of this is suggested by the 
only known Ordovicic formations which was discovered by Sir 
John Evans in Caupolican, Bolivia, and which lies along the strike 
of these Cambric outcrops.^ This Ordovicic section rests upon 
the discovery of very poorly preserved graptolites (Didymograp- 
tus, Phyllograptus, Glossograptus, Cryptograptus ? and Climaco- 
graptus) and trilobites of the genera Peltura, Symphysurus, Trin¬ 
ucleus and Ogygia; both graptolites and trilobites indicating an 
early Ordovicic age.^ 
These Cambric and Ordovicic faunas are too limited to afford 
any clear indications of the relations of land and water during 
those periods or the direction of the invasion, although it was 
probably from the east, and the faunas are those of the Atlantic 
type with which we are familiar in the Northern Hemisphere and 
not decidedly austral as are the subsequent Devonic faunas. It 
may be that both Cambric and Ordovicic will be eventually found 
in what might be termed the pre-Cordilleran, or pre-Andean, re¬ 
gion, northward in Peru and Ecuador, a region practically un¬ 
known geologically, or this earliest Andean geosyncline which lay 
largely to the east of the present Eastern Andes may have had its 
greater portion buried in what is now the central trough of South 
America. As the known Cambric rocks are of Late Cambric age 
and the Ordovicic rocks are of Early Ordovicic age there is evi¬ 
dence of a very considerable break between these early Paleozoic 
rocks and the succeeding Siluric sediments. 
Siluric rocks are known from Amazonas and Para and doubt¬ 
fully from a few other localities in Brazil; there are some more or 
less doubtfully determined rocks in Peru believed to be of Siluric 
age; and there is considerable development of rocks of this age in 
the Eastern Andes from east of Lake Titicaca southward across 
Bolivia to northwestern Argentina. Present evidence indicates 
rather clearly an Atlantic invasion up the Amazonian geosyncline. 
The Bolivian section, which is rather uniform for several hundreds 
2 Ordovicic strata have also been reported from the pre-Cordillera of Argentina. 
3 See Quart. Jour. Geol. Soc. L,ond., vol. 62, pp. 425-432, 1906. 
