GEOLOGY OF PERU—ADAMS. 415 
TERTIARY OF THE SOUTH CENTRAL COASTAL PLAIN. 
The Pisco formation. 
In the low hills to the north of Pisco, which is called “ Cerro de 
Tiza” (meaning chalk), there are exposed white and yellowish rocks 
which have a calcareous aspect much like chalk (see pl. 4). At 
the end of the bridge over the Pisco River they may also be seen, 
and at this place they have steep dips and strike to the northwest. 
This structure is continued into Cerro de Tiza, and crosses the Pisco 
River to the south until the rocks disappear beneath the sands of 
the plains toward Ica. Many outcrops of this formation may be 
seen, especially in the landscape to the south of the railroad station 
at mile 18, but there the beds are practically horizontal. In the Ica 
River valley the same formation is found resting on igneous and older 
stratified and metamorphic rocks. In a hill to the west of the 
Hacienda Ocucaje, in a hill called “Cerro Blanco,” the writer saw 
the remains of a whale embedded in the Pisco formation. There 
w 
Paita formation 
Talara Formations b dg SEA LEVEL 
a 2 A 
[oo o000] | ——— 
Conglomerate Sandstone | Slate [F=----| Phyllite ae 
: ES Sse ===: 
Fic. 7.—Section at Paita, by Grzybowski. 
was also some strata in which a few marine shells are found and 
others in which phosphate nodules occur, but to an extent so limited 
that they have no commercial value. Farther south in the valley 
of the Rio Grande the Pisco formation is cut by the canyon of that 
river. The tributaries of the Rio Grande which flow past Palpa 
and Nazca have cut deep valleys, in the walls of which the forma- 
tion is seen to contain a mixture of rounded stones in a matrix of 
sand and clay materials, but with a sufficient amount of the white 
chalky matter which characterizes the formation to demonstrate 
that it is only a littoral phase of the Pisco formation. 
The Pisco formation is also found in the plains to the east of the 
port of Lomas, where the remains of a whale were seen by the writer, 
and in one of the valleys which cut the plain a conglomerate of ma- 
rine shells was found. To the southward the plains narrow and the 
mountains come to the seacoast, but at Chala there is a small area 
of Pisco formation in which the beds consist largely of variegated 
clays. 
In the northern part of the plains, to the east of the Canete, the 
Pisco formation was found presenting a littoral phase, but containing 
