398 



J. S. DILLER THE JURASSIC FLORA OF OREGON 



association has 3'et been reported. The bulk of it appears to belong to 

 the horizon of Aucella cmssicolUs not far below the base of the Horse- 

 town. 



Distribution of the Shasta and Jurassic Floras in the Klamath 



Mountains of California 



If, as I believe, the isolated areas of plant beds at Eedding creek, Eat- 

 llesnake creek, and Big Bar, on the west slope of the Klamath mountains, 

 in Trinity county, California, are to be regarded as belonging to the 

 Shasta series, then the Shasta series contains both floras ; but, as in Ore- 

 gon, they have not been found together .and their geographic distribution 

 is suggestive. 



The Shasta flora is found widely but sparsely distributed in the beds 

 along the western side of the Sacramento valley and, lapping over the 

 crest of the range, apjDears in the Eedding Creek basin, a few miles from 

 Douglas City. The Jurassic flora of Oregon appears in the region here 

 considered only at Big Bar and Eattlesnake creek. The position of these 

 two localities suggests that the flora may yet be found close to the base of 

 the formation in the Sacramento valley. 



The occurrence of this flora at the very base of the overlapping beds 

 with the little Unio connects the flora definitely with the subsiding coast 

 and the transgressing sea during the Shasta epoch. As the Shasta epoch, 

 M'ith its great thickness of sediments, was a long one, the changes in the 

 flora may have been great, and they would be recorded more or less com- 

 pletely in the si;ccessively newer overla^Dping strata. The changes in the 

 environment of the flora may have been much greater and more effective 

 than those of the fauna, so that in the course of the Shasta epoch the mod- 

 ifications of the flora may have been great, while of the fauna they were 

 comparatively small. 



Kelation of the Monte de Oro Formation to the Mariposa 



The slates of the ]\Ionte de Oro formation, as pointed out by Mr Tur- 

 ner,^* "are very similar to those of the j\Iariposa formation," and it seems 

 most probable, on geographic and structural as well as lithologic and eco- 

 nomic grounds, that the plant beds near Oroville are about the same 

 horizon as the Mariposa formation of the Gold belt. The fossils tend to 

 confirm this correlation, but are not decisive. Tlie extensive association 

 of the slates with volcanic rocks in both the Monte de Oro formation and 



" Seventeenth Annual Report of the U. S. Geological Survey, part 1, p. 548. 



