FAUNA OF THE OXEOTA DOLOMITE. 170 



this cause ; its thickness varies from 50 feet, as at Red Wing, to 250 feet 

 elsewhere. 



Sometimes there are pockets of an argiUaceous shale, like the remnants 

 of rock beds, near the top of the formation, as at Blanchardville, Wis- 

 consin, and Clay Bank, Minnesota, and perhaps always at its top an 

 interstratitication and intermixture of quartz-sand and oolitic dolomite 

 ])revails. Such ])henomena are clearly seen at Mankato and Laneshoro, 

 Minnesota, and many other places. The intervening (lok)mite of these 

 upper beds contains many fossils which disclose the Oneota features. 



The base of the Oneota or the to[) of the Jordan sandstone is always a 

 mixture of quartz, sand and dolomite or an alternation of such layers for 

 several feet. Rarely has the removal of a portion of the carbonate mate- 

 rial by percolating waters given a shar})er demarkation between the two 

 formations. 



FA UNA L CIIA RA CTERS. 



The fauna of the Oneota, so far as known, includes but few species. 

 nor are these abundant. Described species are : 



Rapkistoma (Euomphalus) minnesotensis, Owen. 



Halopea obcsa, Whitfield. 



Orthis pepina, Hall. 

 To which may be added : 



Asaphus, sp. ? 



Lingida, sp. ? 



Murchisonia, sp. ? 



Ophileta, sp. ? 



StriqxiroUu.s, sp. ? 



Endoceras, sp. ? 



Cyrtoceras, sp. ? 



Ascoceras, sp. ? 



Piloceras, sp. ? 

 Tlie richest l(K*alities for fossils are Osceola, Hudscm and Blanchard- 

 ville, Wisconsin ; >hinkat(), Merriam Junction, Redwing, I.ewiston and 

 Stillwater, Minnesota. 



'I'm; Ni;\v Kichmond Sandstonk. 



LOCALITIES. 



In Minnesota: >rankato, Kasota, Cannon Falls, Clay ]>ank, Isinours 

 and Caledonia. 



ill Wisconsin: New Richmond, lUirkli.uts Mills and Argyle. 



In Iowa no locality has yet been seen by the writers. 



This bed was detected in the banks of Willow river, in eastern Wis- 

 consin, in l.S7<;-77, l)y Assistant Geologist L. C. Wooster.* Ko descri])- 



* Geology of WiscoDHin, vol. Iv, 1882, p. 106. 



