1913] 



Louderback: The Monterey Series 



183 



The Santa Clara district would then appear to be exceptional 

 in (1) the opening of Vaqueros sedimentation, (2) its closing 

 phases, and (3) the opening of the supposed correlative of the 

 Monterey, the Modelo. As products of deposition are so 

 abundant here, and as the district is so close to the edge of the 

 Monterey-SanLuis Obispo-Santa Barbara region, these excep- 

 tional features naturally call for further explanation. 



The Opening op the "Vaqueros" Deposition 



In examining the Santa Clara region formations in the field, 

 the writer was continually met by the fact that at the base of 

 the shales called Vaqueros there lies everywhere a sandstone, 

 usually several hundred feet thick, with conformable relation- 

 ship to the shales, which corresponds closely in general nature 

 and appearance to that found at the base of the clay shales else- 

 where, in other words, to the normal opening stage of Vaqueros- 

 Monterey deposition. It has the lithologic character and strati- 

 graphic position of the sandstones to which Fairbanks in the 

 San Luis region would restrict the term Vaqueros. But Eld- 

 ridge and Arnold have separated it from the Vaqueros and 

 grouped it with another formation — the Sespe, calling it the 

 upper Sespe (Eocene or Oligocene). 



A careful study of the Santa Clara bulletin has been made 

 by the writer to learn if possible why these sands were separated 

 from the Vaqueros and united with the Sespe, but without results. 

 According to this report, 7 under the heading ' ' Relation of Upper 

 Sespe Beds to Vaqueros Shale," "No sharp lines of distinction 

 separate the upper Sespe terrane from the underlying red beds 

 or the overlying Vaqueros. On the contrary, there is a percept- 

 ible tendency for the terranes to shade one into another. Fossils 

 of value have not yet been collected from this transitional zone. 

 There is, therefore, some uncertainty as to whether the beds in 

 question should be referred to the Eocene or the Miocene. . . . 

 Tentatively, however, the line between the Sespe (Eocene) and 

 the Vaqueros (lower Miocene) formations has been drawn at an 

 indefinite horizon in the rusty beds described, at a point where 



'U. S. Geo!. Surv. Bull. 309, pp. 11 and 12 (1907). 



