F. II. Knoiolton — Jurassic Flora of Oregon. 53 



belonging to this species have been found well up in the 

 Cretaceous. Giiikgo siherica (or digitata) has already been 

 discussed, while Sequoia ReiohenhacJd has been mentioned as 

 the only species common to the Lower Cretaceous flora of 

 California and Oregon. It ranges through the Cretaceous, 

 principally in the upper part. 



As has been so often stated, the mere presence of a species 

 in a list is not all that is required to make it of value in fixing 

 age. The plant must be abundant in a flora and characteristic 

 of it. It may be a survivor from an older flora, or the first 

 appearance of a form destined to become a dominant factor in 

 a later horizon. It is for this reason that so much stress has 

 been laid on relative abundance of species in the several parts 

 of this paper, but to bring it out still more foi'cibly the follow- 

 ing may be enumerated as filling such requirements : 



Dicksonia oregonensis (close to D. gracilis Heer), Poly- 

 podium oregonense, Tceniopteris orovillensis, Tceniopteris 

 inajor, Tceniopteris vittata, Macroiceniopteris californica, 

 Sager),opteris Goppertiancc, Sagenopteris paucifolia^ Nilsonia 

 orientalis, Nilsonia parvida, Pterophyllum. Hathorsti, Ptero- 

 phyllum contiguum, Pterophyllum cequale, Pterophyllum 

 rajmahalense, Podozamites lanceola,tus, Ctenis sulcicaulis, 

 Ginkgo digitata., Ginkgo Huttoni., Ginkgo lepida, Ginkgo 

 siherica, Taxites zamioides, Brachyphyllum mamillare. 

 Certain of these exist literally in hundreds in the beds. 



Age op the " Jurassic Flora of Oregon." 



Following is Professor Fontaine's* final opinion regarding 

 the age of the beds containing the Jurassic flora : " There 

 can be no doubt, in the opinion of the present writer, that the 

 Yorkshire Lower Oolites, the strata of eastern Siberia and of 

 the Amour, made known by Heer, and the Oregon beds are 

 of the same age. The only question is. What is that age ? 

 The investigations of the English geologists would seem to 



have settled the question for the Yorkshire formation 



So far as my knowledge goes, no one has questioned the cor- 

 rectness of the conclusions of the English geologists regard- 

 ing the age of the Yorkshire strata. That being established 

 as Lower Oolite would certainly indicate a similar age for the 

 Siberian beds and also for those of Oregon." 



The facts that have been presented in the preceding pages 

 regarding relative abundance and world distribution prove 

 beyond any reasonable question that the above statement is 

 correct, and it is confidently asserted that the " Jurassic flora 

 of Oregon " is a tnie Jurassic flora. This age determination 



*U. S. Geol. Surv., Mon. 48, 1905, p. 144. 



