420 E. O. ULRICH REVISION OF THE PALEOZOIC SYSTEMS 



the Carter on the east side of the dome, but until it was proved by un- 

 questionable stratigraphic evidence that the observed differences in the 

 faunas found in the beds next overlying the Lebanon on opposite sides 

 of the dome are truly indicative of successive ages and not merely local 

 variations of a contemporaneous fauna, the final determination of the 

 ages of the respective beds must necessarily have awaited further evidence. 



Having established differential tilting on the Adirondack, Cincinnati, 

 and N'ashville uplifts and proved the consequent absence of deposits on 

 one side that are present on the other by actual superposition elsewhere 

 of formations that seem to occupy corresponding positions on opposite 

 sides of the alternately tilted domes, it is thought reasonable to infer 

 similar tilting of the Wisconsin, Ozark, and Arbuckle uplifts. With 

 respect to the Wisconsin dome, much evidence tending to prove such dif- 

 ferential movements has accumulated, but, as intimated, the actual order 

 of events is so difficult to prove and the evidence so intricate that it is 

 impossible to do it justice in the limited space here available. On some 

 future occasion it is hoped to publish a full discussion of the perplexing 

 structural and stratigraphic problems encountered in the Eopaleozoic 

 rocks of the upper Mississippi Valley. 



The movements and consequent unequal distribution of the deposits 

 within and adjacent to the area of the Ozark uplift are likewise being 

 described in full for a special work on that geologically important area. 

 Here it will suffice to say that tilting of this uplift is clearly indicated 

 by a number of formations covering its flanks. Particularly notable 

 among these are the Yellville, Kimmswick, and certain Silurian and 

 Devonian formations which occur on the south and southeast and are 

 absent on the north and northwest flanks and the extensions southward 

 from Iowa of the Decorah formation, the Prosser limestone, and a Maga- 

 ran dolomite, which formations occur on the northeast margin and are 

 absent on the south and west sides. 



Yellville oscillations. — Of these formations the Yellville is of special 

 interest because it is not only confined to embayments of the old shore 

 of Ozarkia in northern Arkansas and southern Missouri, but also because 

 the formation varies greatly in the distribution of its members. In 

 thickness it ranges from to about 200 feet, but the maximum develop- 

 ment in most of the embayments is less than 150 feet. Neither of these 

 figures, however, does justice to the aggregate maximum development 

 of all the members that are distinguished in Arkansas. This may reach 

 300 feet or more, but satisfactory measurements are difficult to make 

 because vertical exposures are few, and most of the outcrops occur on 

 weathered dip slopes. 



