Paleontology Zorritos Formation 5 



some cases, as will be seen later, his error in the determin- 

 ation of stratigraphic units led to erroneous results. It is 

 apparent in some instances that he mixed his faunas, includ- 

 ing in his collections species undoubtedly not indigenous to 

 the formations from which he was collecting. 



Previous to the work done by van Hoist and Singewald 

 nothing further was published on the Zorritos region. Their 

 work, done during the winter of 1919-1920, was of highly 

 detailed order, covering thoroughly the area indicated above, 

 and extending well inland. The geologic structure of the 

 Zorritos country is so highly complex that nothing short 

 of very painstaking detailed work may be expected to yield 

 results, and superficial examination is almost certain to lead 

 to misconceptions, particularly if the worker confines him- 

 self to the exposures along the coast. 



As a result of their investigation van Hoist and Singewald 

 differentiated the section which is reproduced in figure i. 

 The units there presented will be discussed in downward 

 succession. 



The Payta and Talara formations do not occur in the 

 region from which van Hoist and Singewald collected. The 

 Talara beds appear at the southern end of the area, at Pied- 

 ras Redondas, consisting there of tan gApsiferous shales 

 similar in appearance to the sandy phase of the Heath for- 

 mation. Xo fossils were collected from these beds. Else- 

 where in the Zorritos district, that is. within a radius of 

 ten miles along the coast, with Zorritos at the center, the 

 Talara beds do not appear. 



Grzybowski's Zorritos formation is the same as that 

 outlined by van Hoist and Singewald. with the exception 

 that he confused the \'ariegated beds with the Heath, and 

 did not recognize the upper and lower sandstone members 

 of the formation. It is perhaps best, in order to make 

 clear the necessary revision of Grzybowski's sections, to 

 quote for reference the critical parts of his presentation. 



