The image above shows the Monastery of Roussanou on a spire of Meteora Sandstone in central Greece. The Meteora Sandstone is an Oligocene fanglomerate. The photograph was taken by Gián G. Ori of the Universitá di Bologna and was published on the cover the American Association of Petroleum Geologists Bulletin (v. 68, no. 9) in September, 1984.

        When you've finished admiring the scenery, take a look at the white streak that extends downward from a hole in the foundation of the monastery. I would guess that the white streak is bleached sandstone - sandstone from which ferric iron has been removed - that stands out in contrast to the slightly ferruginous sandstone everywhere else in the image. I would further guess that that the iron was bleached by reducing solutions that reduced iron from its insoluble 3+ state to its soluble 2+ state, so that the iron could be removed. The ''reducing solution" was presumably sewage flowing out of the hole in the foundation of the monastery. It's a striking combination of a beautiful landscape with redox geochemistry.

Railsback's GEOL 8150 (Earth Surface Geochemistry) web page
Railsback's main web page
UGA Geology Department web page