5() F. II. KnowUon — Jurassic Flora of Oregon. 



iiiniiuned or unidentifiable forms found with it, Doctor Stan- 

 ton re]iorts as follows : " T'ne fossils from Big Bar, California, 

 area are certainly upper Knoxville, and hence Lower Creta- 

 ceous, as shown by the presence of typical specimens of 

 Aiicella crassicollis. The other invertebrate fossils from the 

 same area are closely associated stratigraphically with the 

 Aucella, but as tliey are either undescribed or unidentifiable 

 species, they do not throw any additional light on the question 

 of the age of the beds." 



On combining the faunas of Big Bar and Elk River there 

 are found seven named species, of which the most important 

 and characteristic is regarded as Aucella Grassicollis, which 

 Doctor Stanton says " past experience shows to be characteris- 

 tic of the upper part of the Knoxville formation, and is 

 believed to be confined to the Lower Cretaceous." 



The new facts regarding the distribution of the several 

 species of Aucella in the section at Elk River, which resulted 

 from Mr. Diller's re-examination of the area during the past 

 summer and which has already been briefly alluded to [p. 37], 

 is of much significance in the present connection. From this 

 evidence it appears that not only is the principal horizon for 

 Aucella crassicollis in the basal member of the Knoxville and 

 heneath that of the Jurassic plant beds, but Aucella Piockii, 

 supposed to chai'acterize the lower j)ortion of the Knoxville — 

 indeed so occurring in the Elk River section — has been found 

 in the underlying slates of probable Dothan age in association 

 with Aucella Erringtoni, which is a typical Mariposa species ! 

 The wide vertical range here shown for Aucella crassicollis 

 and A. Piochii would certainly seem to disqualify them as 

 diagnostic or key fossils. 



The interpretation that is to be given the Knoxville fauna 

 as a whole may now be considered, and it requires only a brief 

 review of the literature to show that the invertebrate paleon- 

 tologists are not in agreement among themselves as to what 

 this shall be. Thus, Doctor Stanton* regards the entire fauna 

 of the Knoxville formation as of JSTeocomian age. After 

 reviewing the differences of opinion regarding the age of cer- 

 tain Russian beds, he continues : " It is evident, then, that even 

 if it were possible to refer the Knoxville to definite horizons 

 of the Russian Aucella beds, its age might still be questioned. 

 One important fact that should be borne in mind is that struc- 

 turally and faunally, so far as known, the Knoxville is a unit. 

 It is true that there is a gradual change in the fauna from the 

 lower to the upper beds, but there is no distinct break that 

 would justify the reference of one portion to the Jurassic and 

 another to the Cretaceous. There are some elements of the 

 *U. S. Geol. Surv., Bull. 133, p. 30, 1895. 



