GEOLOGY OF PERU ADAMS. 413 



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 Eiver 

 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. 

 It 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 



