418 
PACASMAYDO FORMATION 
AMOTAPE FORMATION 
PISCO FORMATION 
BARRANCO FORMATION 
Pleistocerie Pliocene 
Very recent 
Pleistocene 
Pliocene 
‘Tiocerre 
ANNUAL REPORT SMITHSONIAN INSTITUTION, 1908. 
"Pe comm w. pene 
Fig. 9.—Section correlating the formations of the coast. 
farther in that direction. To the south of Pacas- 
mayo the coastal plains narrow until the mountains 
descend to the shore south in the valley of Viru. 
Throughout this extent the Pacasmayo formation 
is represented in its various phases. The age and 
relations of this formation will be more clearly 
understood when it is considered in connection with 
the Barranco formation next to be described, with 
which it has been correlated (see fig. 9). It is to 
be regretted that in the region of the Sechura desert 
the relations of the Tertiary formations of the north- 
ern part of the northern coastal plains and the 
Pacasmayo of the southern portion are obscured by 
the drifting sands, which obliterates any exposures 
which might otherwise be seen in this area of slight 
relief. 
BARRANCO FORMATION. 
At the valleys of the Pativilca, Huaura, Chancay, 
and Rimac rivers there are sea cliffs cut in what 
appear to be raised delta formations. In other val- 
leys to the south and north smaller areas of a 
similar formation may be seen (see pl. 4). At 
Tambo de Mora the sea cliff has the same character 
as at the mouths of the rivers, but there the forma- 
tion extends inland and northward continuously to 
thé Valley of the Cafiete. The writer regards this 
area, which constitutes a part of the south-central 
coastal plains, as furnishing the key to the proper 
understanding of the Barranco formation. It un- 
doubtedly lies upon the Pisco formation, although 
its relations to the latter south of the Chincha River 
are not very clear because of the intervention of 
the wide stream valley. Its relation to the Pisco 
formation may also be seen in the Cafiete Valley. 
The character of the materials and the degree of 
cementation in the Pacasmayo and Barranco. forma- 
tions is similar. 
No fossils have been found with the excep- 
tion of comminuted shells and occasional branches 
of trees. The writer has assigned the Pleistocene 
age to these deposits and would correlate the coarse 
sediments and bowlders which have been deposited 
in the form and structure of deltas with the in- 
