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J. S. DILLER THE JURASSIC FLORA OF OREGON 



On geographic and stratigraphic grounds, but more especially on ac- 

 count of the associated volcanic rocks and ore bodies, the Monte de Oro 

 formation is regarded as the equivalent of the Mariposa. 



The strata containing the Jurassic flora of the Klamath mountains are 

 conspicuously unconformable to the underlying Paleozoic rocks and con- 

 tain not only a marine, but also a fresh-water fauna. They were de- 

 posited by the sea advancing over the slopes of the subsiding Klamath 

 mountains. 



The same is true of the strata containing the Cretaceous flora found 

 along the western side of the Sacramento valley. 



The two floras have not been found together, but both occur in strata 

 which are lithologically the same, and from their geographic distribution, 

 stratigraphic relation, and contained fauna belonging in part to the upper 

 Knoxville. 



The Cretaceous flora ranges from the upper Knoxville up to the top of 

 the HorsetoAvn, while the Jurassic flora ranges down into the Mariposa. 

 One is confined wholly to the Cretaceous. The other occurs in the Cre- 

 taceous and ranges down into the Jurassic. 



There is a lack of accordance in the faunal and floral evidence as to 

 the position of the line between the Jurassic and Cretaceous. The paleo- 

 botanist would apparently place it somewhere in the upper part of the 

 Knoxville, at a horizon which, as far as yet known, is not marked by any 

 stratigraphic break. On the other hand, the faunal evidence, as inter- 

 preted by American paleontologists, places the line between the Mariposa 

 and the Knoxville. This line is more definitely located as the great un- 

 conformity between the "Myrtle" and the Dothan, base of the Kjnoxville, 

 and marks for the stratigraphic column of the Pacific coast one of the 

 most important tectonic horizons. 



