What is folding?

   Folding is a bending of stratified rock. Beds that are bent into an arch—upward folds—form an anticline. Beds that are bent into a basin —downfolds—form a syncline. A monoclinal fold is inclined in one direction only and is probably better called a flexure. Folds result from horizontal compression of the surface of the earth. They ordinarily extend some distance beneath the surface; frequently erosion, by removing the material at the axis of the fold, exposes the inclined rock units on the sides or limbs of anticlines and synclines. Almost as many variations are attained in the folds of the stratified rock as can be made in a blanket. A few of the terms used to describe them are: symmetric, asymmetric, monoclinal, isoclinal, overturned, recumbent, upright, dome, and basin. Very extensive downfolds, which may contain minor folds of all types, are called geosynclines, and very extensive upfolds are called geanticlines.