io STUDIES IN GEOLOGY, No. i 



Steinmann also recognizes a younger series of red beds 

 of which he gives the following description: (pp. 342-343) 



"Toward the end of the Pliocene and in early Quaternary red 

 sandy rocks were again deposited over a wide area, not as marine 

 sediments, but as continental deposits, and since the Puca sandstone 

 in Pliocene time still covered almost the entire region, at least it was 

 much more widespread than today, these younger continental sands 

 and sandstones were derived chiefly through the destruction and 

 reworking of the Puca sandstone ; they are consequently very similar 

 to it, both in general composition and in color. What, however, 

 could not be repeated and was not repeated in the redeposited 

 material was the regular recurring stratigraphic sequence of the 

 Puca sandstone as well as the intercalations of limestone, gypsum 

 and salt which it contained. Further, since the injection of grano- 

 dioritic rocks and the effusion of trachytic-dacitic volcanic rocks 

 took place at the close of the Tertiary and in the Quaternary, these 

 younger sediments contain almost everywhere fragments and tuffs 

 and even flows of the younger eruptive rocks. There are also 

 local accumulations of pebbles of the old crystalline basement 

 (granite, gneiss, etc.,) which are lacking in the Puca sandstone, 

 and hence constitute another distinguishing characteristic. On the 

 other hand, the oldest beds of these younger sandstones which I have 

 separated from the youngest, certainly diluvial deposits, under the 

 name of Jujuy beds, often overlie the Puca sandstone concordantly 

 and have been folded with it." 



Concerning the mineralogic and petrographic character 

 and the stratigraphic sequence of the Ramos and Vetas 

 formations Steinmann adds nothing to our previous know- 

 ledge, unless it be a greater emphasis upon the shaly 

 character of the Ramos formation. He errs in limiting the 

 fragments and tuffs of the younger grano-dioritic volcanics 

 to his Jujuy beds, as they are found abundantly in the 

 lowest-exposed beds of the Vetas formation. As we shall 

 see later, he also is mistaken in correlating the Vetas and 

 Ramos formations of Corocoro with the Puca sandstone of 

 the eastern Andes. 



Douglas (pp. 27-28) describes all the red rocks of Coro- 

 coro and the surrounding region as one series of red gypsi- 

 ferous sandstones and marls, everywhere marked by- 

 abundant seams of gypsum, often of considerable thickness. 



