F. II. Knowlton — Jtcrassic Flora of Oregon. 61 



Relations between^ Knoxville and Mariposa. 



The evidence that has been presented regardino; the Jurassic 

 flora and its distribution obviously has a bearing on tlie rela- 

 tions between the Knoxville and the Mariposa. As is well 

 known, Dr. C. A. White held that the Knoxville and Mariposa 

 were contemporaneous, at least in part, a view fullj accepted 

 by Doctor Becker, though not generally agreed to by sub- 

 sequent workers in this iield. The two formations have never 

 been found in contact, nor are they likely to be, since one 

 (Mariposa) is found on the western slope of the Sierra JNevada 

 in central California, and the other (Knoxville) on the opposite 

 side of the Sacramento Yalley, mainly against the eastern 

 slope of the Coast Kange. A strong point of agreement is 

 shown by the abundance of Aucellse in both, though they are 

 not now admitted to belong to a single species, as Doctor 

 White believed. Doctor Stanton states that "the faunas, 

 though not large, are entirely distinct, and that of the Mari- 

 posa includes several forms of ammonites that are charactei'istic 

 of late Jurassic the world over, while that of the upper 

 part of the Knoxville contains an equally characteristic array 

 of Cretaceous forms." It is not surprising that there should 

 be a marked difference between the fauna of the Mariposa and 

 the xi])per part of the Knoxville, but when the comparison is 

 made with the lower Knoxville, according to Frof. James 

 Perrin Smith, it shows "a fauna closely related to that of the 

 Mariposa, still witli Jurassic types of Aucella." As a matter 

 of fact practically the entire Knoxville fauna, with the excep- 

 tion of Aucella, has come from the upper 3,000 feet of beds, 

 that is the beds within this distance of the upper range of 

 Aiicella crassicollis, which is fixed as the point separating 

 Knoxville from Horsetown. As thus delimited it comprises a 

 sufficiently distinct faunal group (the Paskenta division of 

 Anderson), but its extension to include the underlying 17,000zb 

 feet of beds which contain exceedingly few of the Knoxville 

 species other than Aucella, is seemingly without adequate 

 support. 



Be this as it may, the relation, if it exists, is throiigh the 

 flora of the Monte de Oro formation near Oroville, which " on 

 geographic and. structural as well as lithologic and economic 

 grounds" has been correlated with the Mariposa. The Oro- 

 ville flora, as already shown, binds it inseparably with the 

 other Jurassic plant bearing areas in California and Oregon, 

 and as pointed out on p. 49, the finding of five characteristic 

 Oroville plants in the Middle Jurassic of the Cook Inlet region 

 is certainly a strong indication that the Mariposa (Monte de 

 Oro) is not the latest Jurassic. 



