GEOLOGY OF PEKU ADAMS. 399 



Carboniferous or Permian. It will be remembered that d'Orbign}^ 

 described Chemnitzia potosensis from the Triassic, but the diagnostic 

 value of the genus for indicating the Carboniferous or Permian may- 

 well be questioned, since the genus is also found in the Mesozoic. 

 Moreover, it will be recalled that the evidence by Steinmann just cited 

 is opposed to the conclusions of Dereims. 



TRIASSIC. 



D'Orbigny (1842) referred to the Triassic a series of variegated 

 reddish sandstones in Bolivia. He found a number of fossils but 

 mentions only one, Chemnitzia potosensis^ the others having been lost. 

 The age of these beds seems to still be in doubt, Dereims having re- 

 ferred them (1906) to the permo-Carboniferous as has already been 

 mentioned. 



Later Forbes (1861) commented on the classification by d'Orbigny 

 and states that it would appear that d'Orbigny proceeded on the 

 supiDOsition that no link in the geologic chain should be deficient. 

 Forbes classed these rocks as Permian or Jurassic, but stated that 

 their age is a question requiring more study. 



Raimondi (1873) in his volume on the Department of Ancachs 

 classed as Triassic certain red sandstones and shales w^ith salt and 

 gypsum. This seems to have been done in accordance with the gen- 

 eral relations of the rocks and to make the geologic succession com- 

 plete. It will be remembered that the fossils sent by Raimondi to 

 Gabb were not given close diagnostic values, and so the classification 

 by Raimondi has really little value. In several places Raimondi 

 speaks of the Triassic as being present, but unfortunately little reli- 

 ance can be placed on this. According to Steinmann's later writings 

 (1904) the red sandstones and shales with salt and gypsum beds are 

 to be classed as Cretaceous (Lower Liassic)." 



JURASSIC. 



D'Orbigny (1842) found no fossils of Jurassic age and did not 

 color any part of his section as Jurassic. He discussed the prob- 

 abilities of its being present in South America. 



Crosnier (1852), in his explorations on the east slope of the Cor- 

 dillera Occidental, found some fossils which were determined by M. 

 Bayle as Jurassic. He mentions an Area like Area gahnelis of the 

 Neocomian. Also an Ammonite from near Oroya was likewise de- 

 termined as Jurassic. 



Forbes (1860) classed as Jurassic or Permian a series consisting 

 principally of sandstones aggregating more than 6,000 feet. These 



° Bol. No. 12, p. 24. 



