I. Bowman — Physiography of the Central Andes. 377 



where the original concordance has been disturbed by differen- 

 tial movements associated with the folding which involved 

 both sedimentary series. In general the folding took place on 

 very broad lines and individual folds are often of great 

 dimensions." The whole of the great region near and south 

 of Tarija consists of a series of shallow folds or parallel chains 

 of Silurian, Devonian, and Cretaceous deposits. The red 

 Cretaceous sandstones rim the outer edge of the entire eastern 

 Andiue section of Bolivia, extending as far as explorations have 

 been carried toward the north. On the south they are said by 

 Hoek to be of marine origin ; but farther north, in the valley 

 of the Juntas and the San Antonio they are certainly terres- 

 trial, carrying large proportions of conglomerate and cross- 

 bedded sandstone. (See p. 374.) Evans has describedf the 

 northeastern section of this marginal band of sandstones as 

 consisting of soft red sandstones and conglomerates overlying 

 harder sandstones in some places, or as a conglomerate resting 

 upon soft shaly sandstones in others. These observations and 

 our own in the valleys farther south, the Juntas and San 

 Antonio, certainly deny a marine origin to the sandstone series 

 of northeastern Bolivia. The age of the sandstones in these 

 northern locations is not fixed, however. They appear to have 

 the same structural relations to the older Paleozoic rocks as 

 the known Cretaceous sandstones farther south and like them 

 also to have been folded on a huge scale and in places block- 

 faulted. It may be necessary to assign a later age to them, a 

 point which seems difficult to clear up in the absence of fossils. 

 The equivalency of the non-marine red sandstones of eastern 

 Bolivia and the marine red beds of known Cretaceous age 

 farther south was first suggested by Steinmann in 18914 



The latest deposits in the central Andes whose age has been 

 positively identified by fossils are of Eocene age and occur 

 along the coast of northern and central Chile. Probable 

 Miocene beds of very limited development occur in northern 

 Chile,§ but neither they nor the Eocene shared in the mountain- 

 making movements of the late Mesozoic. The marine 

 Triassic and Jurassic have a very limited development and 

 occur only between 5° and 25° south latitude in the coastal 

 section of the continent. | 



* Exploration in Bolivia, by H. Hoek (The Geog. Jour., vol. xxv, p. 

 510, 1905). 



f Expedition to Caupolican Bolivia, 1901-1902, by J. W. Evans (The 

 Geograph. Jour., vol. xxii, pp. 607 and 614, 1903,. 



% A Sketch of the Geologv of South America (Amer. Naturalist, vol. 

 xxv, p. 858, 1891). 



SMoricke and Steinmann (X. Jahrbuch f. Min., etc., Beilagebd. x, p. 

 533, 1896). 



|| A Sketch of the Geology of South America. A paper by A. Steinmaun 

 read before the Geol. Soc. Am., Aug. 25, 1891 (Amer. Naturalist, vol. xxv. 

 p. 857, Oct.,. 1891). 



