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



horizon of Strambere, some among them being even very 

 probably identical with these last. There can be no doubt 

 that the lower part of the "Knoxville beds" coi-responds to the 

 upper Portlandian of the Mediterranean region." 



This view is even more revolutionary than that of Professor 

 Pavlow, since if the genus IIojMtes, as represented in the 

 Knoxville, is taken as the gauge of Jurassic age, it will carry 

 with it practically the entire Knoxville fauna, which is found 

 in direct association with one or the other of the five species 

 recognized in this genus. 



More recently still Prof. James Perrin Smith, in an article 

 on "Salient Events in the Geologic History of California,"* 

 has expressed his conviction, based on invertebrate as well as 

 stratigraphic evidence, that the line between Jurassic 'and 

 Cretaceous shall be drawn through the Knoxville and not at its 

 base. He says : "After this mountain-making epoch near the 

 close of the Jurassic, the sea again encroached on the uplifted 

 area, and the Knoxville sediments were laid down on the 

 western border of the Coast Range. The lower Knoxville 

 beds contain a fauna closely related to that of the Mariposa, 

 still with Jurassic types of Aucella, and with the same poverty 

 of other animals. But the upper Knoxville beds, while still 

 retaining reminiscences of the Boreal Region in Aucella and a 

 few other forms, show a preponderance of life chai-acteristic of 

 more favorable conditions. Aucellas of more northerly habit 

 mingle with cephalopods that did not belong in the Boreal 

 Region, and on the nearby land cycads abounded. The line 

 between Jurassic and Cretaceous should be drawn, not at the 

 beginning of the Knoxville but between the lower and upper 

 Knoxville beds ; the former belonging to the Portland and 

 Aquilonian, while the latter belong to the Neocomian." 



Enough has been presented to show that there is more or less 

 difference of opinion regarding the bearing of the invertebrates 

 of the Knoxville on the question of age. 



Relations between Myetle and Knoxville. 



The Myrtle formation takes its name from what is regarded 

 as its typical exposures along Myrtle Creek, Oregon, in the 

 Roseburg quadrangle. In this general area the maximum 

 thickness of the Myrtle formation is estimated by Mr. Diller 

 to be about 6000 feet. It is separated on paleontological 

 grounds into two portions, the later (upper) of which from its 

 contained invertebrate fauna was correlated with the Horse- 

 town of California, while the earlier (basal) portion was cor- 

 related with the Knoxville on the basis of the presence of cer- 

 tain invertebrates but especially Aucella crassicollis and 

 * Science, N. S., vol. xxx, pp. 347, 348, Sept. 10, 1909. 



