GEOLOGY OF PERU—ADAMS. 4138 
In the Brea hills the formation has been thrown up in an anti- 
cline. To the south in the plains region the formation is relatively 
horizontal. To the north of the hills there are steep dips and local 
folds. These may be well seen along the valley of the Tumbez River 
and in the stream which empties into the ocean at Boca de Pan. It 
is interesting to note that the direction of the Brea hills is almost at 
right angles to the trend of the Andes and parallel with the border 
of the Gulf of Guayaquil and with the coast of the Province of 
~Tumbez, which forms the southern part of the Gulf of Guayaquil. 
Moreover, the direction of the dips to the north of the range of 
hills suggests that the folding which produced them was actuated 
from the north. 
The writer has not examined the axis of the range, but has been 
assured by travelers that it contains igneous rocks. Where the 
Tumbez Valley merges from the flank of the hills there are some ex- 
posures of granite, which the writer saw and the presence of which 
was also noted by Grzybowski, but this granite may be older than 
the Tertiary. The anticlinal structure of the range of hills may 
be due to the eruption of igneous rocks which form the axis, but the 
writer did not see anything to indicate this at their western termi- 
nation, and he is inclined to believe that it should be correlated with 
the subsidence which produced the embayment of the coast in the 
region of the Gulf of Guayaquil. 
Grzybowski was the first to study the Amotape formation, and 
what the writer has included under the name “ Amotape formation ” 
has been divided by Grzybowski into the Heath stage, which he 
calls “ Lower Miocene,” and above it the Zorritos and Talara stages, 
which he calls “ Upper Miocene.” He also identified, principally 
upon stratigraphic grounds, the Ovibos stage, which he refers to 
the Oligocene. The exposures which he included in this stage have 
not been seen by the writer, who regrets that he did not have access 
to Grzybowski’s paper until after his own manuscript was written. 
Tt will be remembered that Raimondi sent some fossils from Paita 
to Gabb for determination; the localities from which they were 
collected were unfortunately not sufficiently specific to show whether 
they were from the Amotape formation or not. <A collection of fos- 
sils from Zorritos was also described by Nelson, who made no special 
determination of their age other than late Tertiary, as suggested by 
the title of his paper. 
Pliocene formation at Paita. 
In the sea cliff at the port of Paita the writer observed two for- 
mations separated by an unconformity. The lower he considered to 
be the Amotape. The upper consists principally of sand in imperfect 
sandstone. When he boarded the steamer in the bay the writer made 
