RELATION OF MONTE DE OKO, MARIl'OSA, AND KXOXVILLE 399 



the Mariposa is strilving and in strong contrast with the associated rocks 

 of the later horizons in the Mesozoic. 



Kjclation of the Monte dk Org and Makiposa Foumations to the 



Knoxville 



stratioraphw evidence 



In California the Mariposa and the Knoxville are not found together. 

 TlicY ontcrop on opposite sides of the Sacramento valley. The IMariposa 

 is involved in the intense folding of the Sierra Nevada, is extensively 

 associated with volcanic rocks, has heen considerahly metamorphosed, and 

 contains important ore hodies which have heen successfully mined. The 

 Knoxville lies chiefly against the eastern slope of the Coast range and is 

 not closely folded, altered, or associated Avith large masses of volcanics, as 

 is the Mariposa. It rests unconformably on the strata which appear to 

 have been folded with the Mariposa, and for this reason it is believed 

 that if the Knoxville and Mariposa were found together in California 

 they would be unconformable. This conclusion is in large measure con- 

 firmed in Oregon by the fact that the Knoxville rests unconformably 

 upon the rocks which contain a fauna whose closest affinity is found in 

 the Mariposa. 



FAVyAL BVIDEyCE 



Tt will be recalled that some years ago Dr C. A. White^' regarded all 

 the forms of Aucella yet discovered in the ISTorthern Hemisphere as hav- 

 ing "so close a generic relationship with one another as to hardly exceed 

 the limits which may be reasonably assumed as those of a single species." 

 Doctor White "became satisfied that the AuceJla piochi of the Knoxville 

 and A. erringtoni Gabb of the Mariposa belong to one and the same spe- 

 cies," a conclusion which, as he states, "involved the opinion that at least 

 a part of the series (Mariposa) is equivalent to the Knoxville." This 

 opinion was accepted by Doctor Becker,^' but has not been accepted gen- 

 erally by the paleozoologists and geologists who have studied the problem 

 in the field. 



Doctor Stanton, who has studied the faunas of the Knoxville and the 

 Mariposa in the field more than any one else, is of the opinion that "the 

 faunas, though not large, are entirely distinct, and that of the ]\rariposa 

 includes several forms of ammonites that are characteristic of late Juras- 



''■U. S. Geological Survey Monograph XIH. pp. 226-232. 

 " U. S. Geological Survey Monograph XIII, p. 201. 



XXXVIII— Bull. Gtsol. Soc. Am., Vol. 1!), ino7 



