4 STUDIES IN GEOLOGY, No. 3 



vegetation are those in the larger stream-courses, where 

 small amounts of water support meager plant growth. 



The region from which the fossils described in this paper 

 were collected is in the vicinity of the town of Zorritos, 

 extending about ten miles north and south along the 

 coast, and varying distances inland. It is underlain by a 

 series of Tertiary sediments which have long excited com- 

 mercial interest on account of the petroleum they contain, 

 but which have received scant attention of scientific nature. 

 Oil wells near Zorritos have been productive since 1880, but 

 the location of drilling sites has been almost entirely accord- 

 ing to "wild-cat" methods, and not until recent years has 

 geologic work of any kind been applied to commercial 

 purpose. 



The first study of the geology of the Zorritos region was 

 published by Grzybowski 5 in 1899, as the results of obser- 

 vations made during the course of a trip along the coast 

 north of Payta. He differentiated five formations, from 

 highest to lowest as follows : 



Age Formation Character 



(according to 

 Grzybowski) 



Pliocene Payta .Conglomerates 



Upper Miocene Talara Brown shales 



Lower Miocene Zorritos Sandstones 



Lower Miocene Heath Bituminous shales 



Obligocene Ovibio Massive sandstones 



The ages assigned by Grzybowski to the formations were 

 determined through the study of rather small collections 

 of fossils. The amount of material was too small in most 

 cases to permit the drawing of valuable conclusions, and in 



5 Loc. cit. 



