422 
Slimartr 
Tacond 
‘ ¢ 
g 
8 
y 
8) 
S 
1) 
Devonian YZ ee Wj 
Fig. 12.—Geologic section from Arica to La Paz, by Forbes. 
UpperdolitiiYY, Porphory YA 
ved 
vaya 
a 
— 
INARA, 
* 
XM 
ig 
Qq 
2 
‘S 
8 
iS) 
3 
> 
Alluvium 
ANNUAL REPORT SMITHSONIAN INSTITUTION, 1908. 
Incidentally it may be said that at the 
mouth 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 OF THE ANDES. 
SECTION OF 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 plains 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. 
4 Original in Quart. Journ. Geol. Soc. London, Vol. XVII, Pl. III. 
