GEOLOGY OF PEKU ADAMS. 405 



by Raimondi to Gabb there was a collection from Payta. Gabb, 

 in addition to describing them (1869), states that one set of four 

 or five specimens was made up of extinct forms, while the remainder 

 appeared to be Pliocene. 



Orton (1870) mentions some fossil shells of living species which 

 he collected from the bluff at Payta and which were determined by 

 Gabb. 



The portion of the Tertiary formations of the northern coastal 

 plain lying between Payta and the Ecuadorian frontier was explored 

 and described by Grzybowski (1899). He traveled from Payta to 

 Talara, thence to Tumbez, and up the Tumbez River to Casadero, 

 from which place he returned to the coast. He made the following 

 divisions of the Tertiary : 



Pliocene Conglomerate Payta formation. 



f Brown shales Talara formation. 



Upper Miocene { „ ^ . ry -4. ^ t.- 



[Sandstone ^orritos formation. 



liOwer Miocene Bituminous shales Heath formation. 



Oligocene Hieroglyphic and massive 



sandstone Ovibos formation. 



He collected and described fossils from these formations. The 

 Oligocene, however, he distinguished more from stratigraphic rela- 

 tions than by fossils. The paper is accompanied by a sketch map 

 and sketch sections showing the localities where the formations were 

 found. He observed a granite outcrop at Rica Playa, on the Tumbez 

 River, and called certain rocks in the region of Casadero Paleozoic, 

 but did not identify them by means of fossils. He regarded the Pale- 

 ozoic as pushed up through the broken Tertiary. At Payta he noted 

 a shale formation (no fossils) on which the Tertiary rests. 



Lacustrine Tertiary of the Sierm. 



In the Bolivian Plateau d'Orbigny (1842) described an ancient 

 alluvial and pampean formation, the relations of which are shown 

 in the section accompanying his report. Pissis (1856) also showed 

 this formation but with an interbedded stratum of volcanic tuff in 

 the Titicaca basin region. 



Forbes (1860) described the same deposits under the name " De- 

 luvial of the Interior" and explained that it varies from place to 

 place according to the rocks from which it is derived. In his section 

 he shows locally a bed of trachytic tuff and explained that it is seen 

 in the valley of La Paz, in Bolivia. 



Agassiz (1876), in the paper accompanying his hj^drographic 

 sketch of Lake Titicaca, noted the lake deposits in the Titicaca basin 

 and said that there are terraces up to 300-400 feet above the present 

 level of the lake, and made some comments as to its former exten- 



