7-i //. E. Gregory — A Geologic Reconnaissance 



Avicula sp. A small simple form resembling A. linguiformis. 



Cucullaea sp. A small, rather short form without distinctive 

 sculpture. 



Cardita sp. A strongly sculptured form not exceeding an inch 

 in height or length. 



Pleuromya sp. A single small specimen apparently belonging 

 to this genus. 



Naticaf sp. Several casts of small stout natieoid shells which 

 may include more than one species and possible more than one 

 genus. 



Turritellaf sp. Two very small casts which do not retain the 

 sculpture. 



Fasciolaria? sp. A single specimen doubtfully referred to this 

 genus on account of form and sculpture. 



Cinuliaf sp. An imperfect cast and an imprint of part of the 

 surface. 



There can be little doubt that these fossils are Mesozoic and 

 probably not older than Cretaceous. In the absence of Ammonites 

 and other characteristic types for closer age determinations it 

 would be imprudent to assign them to a definite horizon, though 

 I think it most likely that they belong to the Upper Cretaceous." 



Limestones of identical character and containing fossils of 

 the same age remain as patches on the Fortaleza, Catunga, and 

 Machu highlands and are exposed in thick beds near Ayus- 

 bamba, on Apurimac River 15 miles south of Cuzco, as well as 

 at points farther west. The preservation of remnants of once 

 widespread Upper (?) Cretaceous limestone is believed to have 

 resulted from the development of downsunken fault blocks. 



The Yucay limestone is extensively used in construction for 

 walls, foundations, pavements, and also in chiseled blocks for 

 buildings. The famous Inca fortress of Sacsahuaman is built 

 of enormous blocks of Yucay limestone brought from a quarry 

 about 1 mile distant. 



Bambanusa Formation. 



The sandstones exposed along the eastern edge of the Bam- 

 banusa Parnpa north of Ccasa-Cancha constitute the Bambanusa 

 formation. Typical outcrops south of the Ichchu-Orcco lava 

 field are white or light gray in tone; the unweathered rock is, 

 however, in many places pink in color. Pure quartz sandstone 

 with sugary texture is the predominant rock type, and its con- 

 stituent grains are so feebly held together by cement that the 

 rock crumbles under a blow of the hammer and piles of clean 

 quartz sand are found at the base of cliffs. Erosion favored 



