1913] 



Louderback: 



The Monterey Series 



21!) 



(Mactra montereyana Arnold and Venericardia montereyana 

 Arnold) have not as far as known to the writer been reported 

 from any locality but that of original discovery, and their geo- 

 logic relations are unknown. 



The thickness of the "Monterey shale" is given as 5000 ± 

 feet, of the Vaqueros sandstone 2700 ±. 



In the Santa Cruz Folio, then, the rocks of the Monterey 

 series have been presented as two distinct formations apparently 

 separated lithologically, faunally, and representing two epochs 

 of deposition (lower Miocene and middle Miocene respectively), 

 and separated in part by an unconformity. But a critical esti- 

 mation of the evidence presented indicates that the divisions 

 have been made throughout on lithologic difference (depositional 

 facies), that the unconformity is not evident where exposures 

 are clear but only suspected in certain areas where contact areas 

 are hidden and even if present we have no reason to suspect that 

 it marks the time of supposed depositional or (and) faunal 

 change. Furthermore, the supposed characteristic fauna of the 

 Monterey is chiefly a shale facies, whose forms are known to 

 the base of the Miocene and in large part into strata supposed 

 to be Oligocene (San Lorenzo) or Eocene (Coalinga Tejon shale) 

 and containing no element that is even fairly surely known to 

 characterize a "Monterey shale" or "middle Miocene" time 

 period. It is evident that this area which seemed at first to offer 

 especially good grounds for the distinction is on no stronger 

 basis than others already discussed. 



Environment of Tertiary Faunas, Arnold, 1909. — A general 

 statement of Arnold's views appeared this same year. 66 As the 

 individual papers in which his evidence is presented have already 

 been discussed, this general paper (in which no evidence is pre- 

 sented) may be passed over without discussion. 



Coalinga Oil District, Arnold and R. Anderson, 1910. — In 

 1910 Arnold and Robert Anderson published 07 an extensive 

 report on the "Geology and Oil Resources of the Coalinga Dis- 

 trict." The "Vaqueros sandstone (lower Miocene)" is de- 



60 Arnold, Environment of the Tertiary Faunas of the Pacific Coast of 

 fhe United States, Jour, of Geol., vol. 17, pp. 509-533 (1909). 



«7TJ. S. Geol. Survey, Bull. 398 (1910). See also the Preliminary Re 

 port, Bull. 357 (1908), and the Palaeontological Report, Bull. 396 (1909). 



