1913] 



Louderback: The Monterey Series 



213 



"The Vaqueros and Monterey terranes taken as wholes are 

 distinct units, representing periods of deposition of entirely dif- 

 ferent character. 58 As indicated by the rocks, deposition was 

 continuous between the Vaqueros and Monterey and the change 

 in character came suddenly, although less so in some places than 

 in others. The general nature of the Vaqueros series is detrital ; 

 that of the Monterey organic. The former contains many well 

 preserved molluscan forms, the latter few. Close to the line 

 between the two, beds predominatingly of a gravelly or sandy 

 nature or those bearing fossil mollusks are considered part of 

 the Vaqueros ; those of a fine texture and of flinty or opaline 

 or chalcedonic nature, part of the Monterey" (p. 34). 



"A paucity of recognizable molluscan fossils is one of the 

 prominent characteristics of the Monterey in this region, as in 

 most others in the Coast Ranges where it outcrops. Moreover, 

 the other fossils that it contains are of little value in indicating- 

 its age. Its position in the geologic column is determined by the 

 lower Miocene fossils found just below its base in the Vaqueros 59 

 and by the upper Miocene fossils found at or near the base of the 

 Fernando formation which lies unconformably above it" (p. 47). 

 Yet it is said ' ' These shales make up the Monterey formation and 

 are probably representative of the whole of middle Miocene time" 

 (p. 33). 



We have here a confession of the flimsy evidence upon which 

 the "period of deposition" of the siliceous shales is determined. 

 The alternation of organic shales and sandstones ("Vaqueros") 

 found in the Los Angeles district and the rapid fluctuation in 

 the relative proportions of "Monterey" and "Vaqueros" in the 

 Santa Maria district (see p. 191) apparently did not lead the 

 writers to see that these two types were merely depositional facies, 

 and that the line drawn between them in the Santa Maria field 

 while lithologic, and having an important economic and geologic 

 bearing, in no sense represents a horizon or division line between 

 the "lower Miocene" and "middle Miocene." 



Whatever period of time referred to the European scale the 

 rocks of the Monterey series of the Santa Maria district repre- 

 ss Italics supplied, 

 so Italics not in original. 



