Anticline with Saddle Reef

Anticlinal fold in sandstones and shales, United Kingdom. The white material in the hinge of the fold at the center of the photograph is quartz, and fills a void that opened up during folding. Such filled-in features are called saddle reefs. The axial plane dips steeply to the right. The fold has a tight but rounded hinge. Photo credit: John Ramsay.