SOUTH AMERICAN GEOLOGY 
195 
of miles along the strike, lies largely to the east of the present 
divide of the Eastern Andes, and shows the following general 
succession: 
White quartzite, with Scolithus. 
Sandy shales, packed with large Lingulas. 
Heavy gray sandstone, the socalled Bilobites sandstone. 
Dark pyritiferous shales, with geodes. 
Middle quartzite. 
Graptolitic shales. 
Lower shales and quartzites. 
Except for the Lingula beds and the erosion-resisting sand¬ 
stones the Siluric rocks are only sparingly fossiliferous, and they 
appear to represent very shallow water sediments. To be sure 
details are usually not made out in reconnaissance and doubtless 
there were changes of level during the Siluric Period and a shifting 
of the geographic pattern; but the time has not yet arrived for 
determining these changes or even for allocating the South Amer¬ 
ican Siluric succession in the standard world-section. 
We know more about the Devonic formations, not only because 
of their greater areal extent, but because of their more 
abundant fossils, which have been rather fully described, 
principally by A. Ulrich, R. Knod, F. Katzer and John M. 
Clarke. The last mentioned author has discussed this austral 
Devonic forms in several papers, chief of which, his recent (1913) 
monograph on Parana Paleontology, is a most scholarly and com¬ 
prehensive summation of all that was known of the Devonic rocks 
of South America and their relations to the Devonic sections of 
other areas. The Devonic rocks are predominantly sand- and 
mud-stones, hence the prolific, dear-water, calcareous faunas are 
largely wanting, and although certain localities, such as those 
around Lake Titicaca and near Tarabuco, Bolivia, are notable for 
their fossils, one may ride for days over the black, partially meta¬ 
morphosed Devonic shales in the Eastern Andes without seeing 
much except occasional Nuculites-like bivalves and the ubiquitous 
Oriskany Leptocoelia flabellites which latter is so abundant and 
widespread that someone has christened this austral Devonian land- 
mass “Flabellites Land.’’ 
No Devonic beds have been found in, or west of, the Western 
Andes, and that region is believed to have remained a land area. 
There is also good evidence of land at this time in the northern 
