640 E. O. ULRICH REVISION OF THE PALEOZOIC SYSTEMS 



near Whitehall, New York. Finally, not less than six of the species 

 found at Chepultepec have been identified in collections from the upper 

 part of the Oneota dolomite in Wisconsin, Iowa, and Minnesota. From 

 these occurrences it appears that the Gasconade-Chepultepec faunal zone, 

 though only locally developed, is yet widely distributed in America, and 

 perhaps the most easily identifiable of the Ozarkian horizons. 



The Ozarhian in the upper Mississippi Valley. — In tlie u])j)('r ]iart 

 of the Mississippi Valley the Ozarkian includes four long estal)lished 

 formations, namely, (1) the Mendota dolomite, (2) the Jordan sand- 

 stone (Madison sandstone of Wisconsin), (3) the Oaeota dolomite, and 

 (4) the Shakopee dolomite, the last including the New Eichmond sand- 

 stone, which is thought to indicate an introductory clastic phase of the 

 Shakopee rather than a distinct formation. The Mendota dolomite is 

 commonly identified with the Saint Lawrence limestone of Minnesota, 

 but I am not convinced that this relation is a fact. Unfortunately I 

 have had no sufficient opportunity to study this problem in the field; 

 and the fossils from beds between the Dresbach below and the Oneota 

 above now in my hands are far from satisfactory in kind, number, and 

 exact stratigraphic assignment. The few labeled Mendota limestone 

 suggest no other than species found in the Eminence formation in Mis- 

 souri. On the other hand, the only time I saw beds on the west side of 

 the Mississippi occupying the position and supposed to be of Saint Law- 

 rence age, namely, at Lansing, Iowa, I satisfied myself that their lower 

 part at least represents some portion of the Elvins in Missouri, and hence 

 is of late Cambrian age. At present, then, it seems not improbable that 

 the upper Mississippi Valley sections include two thin formations, dis- 

 tinct in age and geographic distribution, between the Dresbach and the 

 Jordan. 



Eegarding the age of the Oneota we know certainly only this, that its 

 upper part contains a considerable and quite unquestionable Gasconade 

 fauna. It is therefore older than the Eoubidoux and possibly all Gas- 

 conade. But the collections in the National Museum include other small 

 lots of fossils marked as coming from the "Lower Magnesian" in Wiscon- 

 sin (especially EHot's quarry, near Baraboo) and Minnesota that seem to 

 be older and probably of the age of the Eminence. If these really belong 

 in the Oneota, then the Jordan sandstone and the Mendota limestone may 

 both be older than the Eminence. This possibility, which in fact I re- 

 gard as very remote, has nevertheless influenced the tentative arrange- 

 ment of these formations in the correlation table. Whatever the final 

 arrangement may be, it seems certain now that the Ozarkian will be 



