12 STUDIES IN GEOLOGY, No. i 



Singewald and Miller (pp. 171-172) state that: 



"the country rock of the district consists of a thick series of prevail- 

 ing red gypsum- and iron-bearing shales, sandstones, and conglom- 

 erates, the relative abundance of which ranges in the order named. 



The prominent characteristic of the series as 



exposed in this hill [the Vetas formation] is the abundance of 

 sandstone beds ranging in thickness from one to several meters. 

 . . In the series of rocks out-cropping in this ridge [the 

 Ramos formation] sandstones are less prominent and shales more 

 abundant." 



This brief description emphasizes the sandy character of 

 the Vetas formation and the shaly character of the Ramos 

 formation, but does not call attention to the gypsiferous 

 character of the latter and the lack of gypsum in the former, 

 nor to the presence of fragmental igneous and tuffaceous 

 material in these sediments. 



Lincoln's description of the Corocoro beds is limited to 

 the statement that: 



"Corocoro is situated in a group of low hills composed of shales, 

 sandstones, and conglomerates ranging in age from Triassic to late 

 Tertiary. These sediments have a general ferruginous color, and 

 are also gypsiferous." 



None of the distinctive features of either series of rocks is 

 mentioned. 



The foregoing descriptions of the Corocoro strata are 

 generalized impressions of the various observers. There is 

 considerable disparity in the emphasis laid upon the various 

 characteristics of the beds as a whole and upon the distinctive 

 features of the series of beds on each side of the main fault 

 line. But a composite picture of all the descriptions gives 

 a good general idea of what the two series of rocks are like. 

 In order to present this information in more accurate and 

 detailed form, the authors measured' two sections of the 

 Vetas beds, one with transit and stadia rod and the other 

 by pacing, and one section of Ramos beds with transit and 

 stadia rod. 



