178 HALL AND SARDESON — THE MAGNESIAN SERIES. 



In later instances Winchell used the term Shakopee for the Shakopee 

 horizon* only, and by error designated the lower portion and the in- 

 tercalated sandstone as Saint Lawrence limestone and Jordan sandstone 

 respectively. 



Subsequent discoveries by Warren Upham in the Minnesota river 

 valley ,t which harmonized with earlier observations by L. C. Wooster in 

 Wisconsin, J led to the recognition by the writers in 1892 of the Shakopee 

 A dolomite (= Shakopee) ; Elevator B sandstone (= New Richmond), 

 and Shakopee B dolomite (= Oneota) ; Lower Magnesian limestone, 

 Owen ; main body of limestone, Irving ; Shakopee B limestone, Upham, 

 and at least six different terms or designations used at different times by 

 N. H. Winchell § as terms take precedence over McGee's Oneota; but 

 inasmuch as it seems impracticable to free the older terms from a great 

 burden of error and complication the new and clearly defined term 

 Oneota of McGee is preferred. Further, the term Oneota is the only one 

 of all hitherto used which is referred to a typical locality. 



PHYSICAL CHARACTERS. 



The Oneota is typically a porous dolomite in heavy, uniform layers. 

 Generally in the upper part the formation has been penetrated by nu- 

 merous water channels, leaving cavities and fissures which are now lined 

 with finely crystalline quartz or filled with quartz concretions. The 

 original stratification is doubtless wholly obliterated and the pseudo- 

 stratification, which now occurs and is in many places sharply distinct 

 is much disturbed. This is generally true for the upper portion of the 

 formation and more rarely for the formation as a whole, as at Point 

 Douglas, Minnesota. At this locality layers several feet in thickness are 

 squeezed out in the distance of a few paces. Accompanying this dis- 

 turbed and compressed condition of the dolomite is a compact texture, 

 which in turn is frequently associated with a fractured, brecciated or 

 pseudoconglomeratic structure, or even with foreign material, as sand 

 grains imbedded in the cracks and seams. The disturbed condition of 

 the pseudostratification leads to a thinning out of the beds within small 

 areas. Sometimes the whole formation seems to be undulated, as at 

 Ottawa, Minnesota, while elsewhere the base of the formation is hori- 

 zontal and the irregularity of lamination and undulation increase toward 

 the top. The upper surface of the Oneota is perhaps always uneven from 



* Bull. Minn. Acad. Nat. Sciences, 1875, vol. i, p. 15G ; Geol. and Nat. Hist. Survey Minn., Final Rep., 

 vol. i, 1884, p. 219. 



fSee Hall and Sardeson, Paleozoic Formations of Southeastern Minnesota, Bull. Geol. Soc. 

 America, vol. 3, 1892, p. 341, 



J Geology of Wisconsin, 1882, vol. iv, p. lOfi; loc. cit., p. 342. 



§Hall and Sardeson, Bull. Minn. Acad. Nat. Sci., vol. iv, No. 1. 



