STRATIGRAPHY 733 



cypod, Nuculites sp., which were obtained from dark shales in the 

 Quebrada de Los Monos. These fossils were beyond doubt from the 

 strata here named the Los Monos shale. According to Bonarelli, they 

 indicate the Devonian age of the inclosing beds, which he correlates with 

 the Icla shales, a formation which outcrops over wide areas in the 

 Bolivian and Argentine territory to the west and southwest of the Front 

 Eanges. 



Dr. Bonarelli also describes the following fossils from the lowermost 

 beds in the Sierra de Mandiyuti : Rensellaria falklandica, Leptocoelia 

 flabellites, Orthis pectinata, Rhynchonella? sp., Schizobolus sp. This 

 also is a Devonian fauna and its description confirms the tentative con- 

 clusion that the lowest beds in the Sierra de Mandiyuti are of similar 

 age to those in the Quebrada de Los Monos. The greater amount of 

 sand at the Mandiyuti exposures would suggest the possibility of close 

 correlation between the strata there and the Huamampampa sandstones 

 which overlie the Icla shales in the western part of the Cordillera 

 Oriental. 



Although in some respects the Los Monos shales resemble the Espejos 

 formation, and the fossils found in each indicate their correspondence in 

 age, it is thought wise to retain separate names for the two. The beds 

 at the north contain a considerable percentage of limestone, which is 

 entirely lacking from the southern localities. Should the two be proven 

 contemporaneous when more detailed studies are made, it would probably 

 be best even then to indicate the lithologic differences by individual 

 formation names. 



BERMEJO SERIES 



Origin of the name and limit of the series. — The name Bermejo series 

 was first applied by Healcl and Mather (1922) to the thick series of 

 sandstones, shales, and conglomerates intervening between the Totora 

 series and the Cajones limestone in the Cordillera Oriental, north of the 

 eighteenth parallel. From these more northerly localities the beds have 

 been traced with practical continuity into the region now under dis- 

 cussion. 



The upper limit of the Bermejo series in the Front Eanges, south of 

 the eighteenth parallel, has been placed at the lower surface of a lime- 

 stone, or limestone and chert, formation which is believed to be correctly 

 correlated with the Cajones limestone of the Sierra de Santa Cruz. This 

 overlying limestone chert horizon is the "Horizonte Calcareo-dolimitico" 

 of Steinmann and Bonarelli. According to Steinmann, the fossils in 

 that formation suggest its Cretaceous age, but the more representative 

 collections described by Bonarelli in his recent contribution (1921) un- 



