422 



ANNUAL KEPOET SMITHSONIAN INSTITUTION, 1908. 







Q. '^ 



Incidentally it may be said that at the 

 month of the canyon just north of Pisagua 

 in Chile similar terraces may be seen, the 

 upper one being at an elevation of some- 

 thing more than 1,000 feet. 



These terraces, taken together with the 

 elevation at which the Pliocene Tertiary 

 formations on the coast are found, record 

 the rising of the land. Accordingly, the 

 upper terraces may be Pleistocene and the 

 lower ones Recent, but there is nothing to 

 indicate two periods of movement, and the 

 spacing and disposition of the terraces cut 

 in the Pisco formation indicate a gradual 

 elevation. 



Geologic Sections or the Andes. 



SECTION OP SOUTHERN PERU, ARICA TO LA 

 PAZ, BY DAVID FORBES (1860). 



If the general section of Peru by Forbes °' 

 (fig. 12) is divided so that it may be com- 

 pared with the succession of zones parallel 

 to the trend of the Andes, as distinguished 

 by Steinmann at a later date, the follow- 

 ing may be enumerated from the coast 

 toward the interior: 



1. Mesozoic sediments with interstratified 

 porphyries of the coast range (at Arica). 



2. The Tertiary (and diluvial) forma- 

 tion of the coast jilains with trachytic tuffs 

 and ash beds. 



3. The diorites of post-Cretaceous (post 

 oolitic) age. 



4. The Mesozoic sedimentaries with in- 

 terstratified porphyries of the western 

 slope of the Cordilleras cut by diorites. 



5. Volcanic trachytes and trachytic 

 rocks of the Cordillera Occidental cutting 

 the Mesozoic sedimentaries. 



6. Zone of Paleozoic (Carboniferous and 

 Devonian) sediments of the Titicaca basin 

 with later " diluvial," including a bed of 

 interstratified trachytic tuff. 



« Original in Quart. Journ. Geol. Soc. London, Vol. XVII, PI. III. 



