F. H. Knowlton — Jurassic Flora of Oregon. 59 



Aucella Piochii. The first mentioned species of Aucella, Mr. 

 Diller says,* "is characteristic of the later portion of the 

 Aucella-bearin^ beds immediately adjoining the Horsetown 

 beds. In California these forms are found in the Knoxville 

 beds, which lie below and are older than the Horsetown beds." 

 In his latest published words on the relations of the Myrtle 

 formation Mr. Diller continues as follows :t "At the base of the 

 'Myrtle formation' in Oregon there is an important uncon- 

 formity and overlap. The successively newer, overlying strata 

 of the 'Myrtle' in general lap over further and further 

 inland beyond the limit of the older strata of the same series, 



i'ust as the members of the Shasta series do in California, 

 i'urthermore, the lower portion and greater part of the 

 'Myrtle formation' is characterized by a fauna in large 

 measure identical with that of the Knoxville beds, while the 

 top part contains a fauna closely related to that of the Horse- 

 town beds. There is good reason, therefore, for regarding the 

 Shasta series of California and the 'Myrtle formation' of 

 Oregon as equivalent." 



To this statement there is but one conclusion possible, 

 namely — that Mr. Diller regards the Myrtle as a whole as the 

 equivalent of the Shasta as a whole, the latter naturally includ- 

 ing both Knoxville and Horsetown. As the newer part of the 

 " Myrtle formation " corresponds to the Horsetown, so the 

 earlier part corresponds to the Knoxville. That this earlier 

 portion of the Myrtle really corresponds to the whole of the 

 Knoxville is shown, as at Elk River, Thompson Creek, etc., 

 by the presence in it of a Jurassic flora, and Aucella P-iochii, 

 which latter is held to characterize the lower Knoxville. On 

 the other hand, from the presence of Aucella crassicollis in 

 association with the Jiirassic plants in this earlier portion of 

 the Myrtle, the whole of this portion is held by some to be 

 equivalent to the upper pai-t of the Knoxville just below the 

 Horsetown — in other words, that there is nothing in the 

 Myrtle section corresponding to the middle and lower portions 

 of the great Knoxville section. This view would seem to 

 involve some paleontologic, as well as stratigraphic, difficulties 

 or anomalies. First — If the lower portion of the Myrtle 

 corresponds only to the upper part of the Knoxville, then it is 

 hardly correct to say that the Myrtle as a whole is the equiva- 

 lent of the Shasta as a whole. Second — As already pointed out, 

 Louderbach, on structural and lithologic groimds, regards the 

 lower portion of the Myrtle as referable to the Franciscan of 

 California. To correlate this with the upper part of the 

 Knoxville would certainly do violence to this view. Third — 



*Eoseburg folio, No. 48, p. 2, 1898. 



f Geol. Soc. Am., Bull., vol. xix, p. 396, 1908. 



