This extreme southern Ohio outcrop exposes fluvial sandstone laid down during the Coal Age, Pottsville and Allegheny Groups (near transition), Pennsylvanian System, Lawrence County, Ohio. You can see this outcrop a kilometer off road in Wayne National Forest near N38 42' 59" W082 41' 11".
|A remote promontory, Wayne National Forest, Lawrence County, Ohio. A large slump block separated along a pronounced, inclined rock joint is seen at upper right.|
Weathering and groundwater movement has dissolved iron oxide cement beneath the rock surface and redeposited the cement in the outer centimeters of the outcrop surface, resulting in case-hardened surface layers. Loss of cement underneath the case-hardened surface has reduced the bond between the surface layer and the rock mass underneath. Addition of cement in the surface layers increases their volume creating tension between the surface layers and the underlying sandstone. The outer layer is exfoliating, exposing less weathered sandstone.
Porous and permeable sandstone bedrock often preserves detailed structures, coarse and fine, long after the sediment is lithified. Differential erosion, harder structures outlasting softer structures, can emphasize rock structures. The chemical properties of bedrock cement, in this case, iron oxides, result in the variations of hardness as well as colorful appearance. Liesegang bands, alternating color bands and sometimes swirl and ring patterns, result from diffusion-reaction properties of mobile iron oxides and other cementing chemicals.
|Cross-bedding interrupted by a cavity.|
*Lawrence County, Ohio is part of the Hanging Rock Iron District of southeast Ohio and Northern Kentucky. The clean removal of case-hardened slabs seen in the image may be the result of ore diggers using long-handled tools to break free iron rich slabs to top off a ox cart load of the Feruginous Ore gathered nearby.