F. H. Knowlton — Jurassic Flora of Oregon. 33 



Art. IV. — The Jurassic Age of the '' Jurassic Flora of 

 Oregon^'' ;* by F. H. Knowlton. 



Introduction. 



Thk stratio-raphic and paleontologic relations of the earlier 

 Mesozoic rocks of the Pacific Coast region, more particularly 

 the Knoxville and related formations, have been the subject 

 of prolonged investigation, and, it may be added, not a little 

 difference of opinion as regards their interj^retation. Mr. J. S. 

 Diller, of the U. S. Geological Survey, is especially notable 

 among those who have made this area the subject of study, and 

 to his interest and energy we are principally indebted for the 

 bringing to light of the numerous and often exhaustive collec- 

 tions of fossil plants. To Prof. Lester F. Ward and Prof. 

 Wm. M. Fontaine Ave are also under obligation for the 

 adequate study, illustration, and publication of these floras, 

 without which they would, doubtless, have long remained 

 unavailable for stratigraphic uses. Although the story told by 

 the floras is seemingly plain and unequivocal, the conclusions 

 of the paleobotanists have not always been given full considera- 

 tion, and it is the object of the present paper to present this 

 paleobotanical evidence in compact form, together with such 

 stratigraphic and other paleontologic data as may be necessary 

 to make the position clear.-j- 



In November 1908, Mr. Diller published a paper under the 

 title, "Strata containing the Jurassic Flora of Oregon, ":{: the 

 thesis of which lie sets forth as follows : "Two fossil floras 

 have been reported from the Mesozoic rocks of California and 

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

 former the fauna is Cretaceous, but with the latter the faiina 

 has been regarded as a matter of doubt. It is the purpose of 

 this paper to remove the doubt by showing that in parts of 



Oregon and California the Jurassic flora, is in 



the 'Myrtle' and Knoxville beds, while elsewhere it extends 

 down to the horizon of the Mariposa, and the general conclu- 

 sion is reached that for the Pacific Coast the line between the 

 Cretaceous and the Jurassic is the great unconformity at the 

 base of the Knoxville." 



The major portion of Mr. Diller's paper is devoted to proof 

 that the Jurassic flora occurs ' in the Knoxville formation — a 



* Published with the permission of the Director of the U. S. Geological 

 Survey. 



f The writer labors under the disadvantage of not having seen in the field 

 the several formations here involved, and consequently the discussion is 

 confined mainly to the paleobotanical evidence. The geological data are 

 largely from Diller. 



^Geol. Soc. Am,, Bull., vol. xix, pp. 367-403, 1908. 



Am. Jour. Sci. — Fourth Series, Vol. XXX, No. 175. — July, 1910. 

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