444 A. W. GRABAU PALEOZOIC DELTA DEPOSITS OF NORTH AMERICA 



6 and 7). A disconformable contact with the underlying formations is 

 further indicated by the Clinton of Ohio, which contains well-rounded 

 foreign pebbles in its basal portion. The fact that the Juniata and suc- 

 ceeding Siluric deposits of central Pennsylvania are essentially concor- 

 dant in dip y though separated by a disconformity and hiatus, shows that 

 the effect of the post-Ordivicic folding was not felt as far west as this 



Figure 6. — Section of the Oolitic Iron Ores of the Lower Siluric (2) resting discon- 

 formaoly on Haquoketa Shales. Iron Ridge, Wisconsin 



region. The absence of Juniata and Bald Eagle beds in eastern Penn- 

 sylvania, where they must have existed, since the material of which they 

 are composed could only have been derived from the old land still farther 

 to the east, is explained by the fact that the Taconic folding carried the 

 bottoms of the synclines above the present erosion plane. When it is 

 remembered that these folds were truncated, and that the region was 

 essentially peneplaned in early Mesozoic time, and that, finally, Tertiary 



Figure 7. — Cross-secticn of the Iran Deposit at Iron Ridge, Wisconsin 



1. Maquoketa shale, marked at the top by a layer of polished pebbles ; 2, cross-bedded 

 oolitic iron ore ; 3, Maysville limestone 



erosion has affected primarily this eastern belt, it is not surprising that 

 all vestiges of the former eastward extent of these formations have been 

 removed. 



If we consider that the first effect of folding in this region was to 

 throw the red Juniata beds into relief, and with these the underlying 

 white Bald Eagle quartzites, we are compelled to recognize that the first 

 fruit of subsequent erosion would be an abundance of red (or highly 

 oxydized) material, followed by white quartzitic material, when the axes 



