368 J. S. DILLER THE JURASSIC FLORA OF OREGON 



Page 



Plant beds of Oroville, California 387 



Historical 387 



Lithology 388 



Auriferous quartz veins 388 



Distribution 389 



Structure and thickness 389 



Relation to adjacent volcanics 389 



Fossils and age 390 



Horizon of Aucella crassicollis 391 



Local silicification of the "Myrtle formation" 392 



"Myrtle" generally unaltered 392 



Exception to general rule 392 



Calcareous cement and quartz veins in the "Myrtle" 392 



Calcareous cement and quartz veins in the Dothan 393 



Age of the rocks 393 



Local silicification at the close of the Knoxville 394 



Relation of the "Myrtle formation" of Oregon to the Shasta series of Cali- 

 fornia 395 



Distribution of the Shasta flora in the "Myrtle formation" of Oregon 396 



Distribution of the Jurassic flora in the "Myrtle formation" of Oregon. .. . 397 

 Distribution of the Shasta and Jurassic floras in the Klamath mountains 



of California 398 



Relation of the Monte de Oro formation to the Mariposa 398 



Relation of the Monte de Oro and Mariposa formation to the Knoxville. . 399 



Stratigraphic evidence 399 



Faunal evidence 399 



Vertical range of Aucella and the two floras in California and Oregon 400 



Limit between the Jurassic and Cretaceous 400 



Summary 401 



Introduction 



PROBLEM AND CONCLUSION 



Two fossil floras have been reported from the Mesozoic rocks of Cali- 

 fornia and Oregon, the one Cretaceous and the other Jurassic. With the 

 former the faima is Cretaceous, but with the latter the fauna has been 

 regarded as a matter of doubt. It is the purpose of this paper to remove 

 the doubt by showing that in part of Oregon and California the Jurassic 

 flora, as illustrated in the accompanying diagram, is in the "M}Ttle" and 

 Knoxville beds, while elsewhere it extends down to the horizon of the 

 Mariposa, and the general conchision is reached that for the Pacific coast 

 the line between the Cretaceous and the Jurassic is the great unconform- 

 ity at the base of the Knoxville. 



