CLASSIFICATION OF FOLDS 



239 



cal and bisects the fold into equal halves. In asymmetrical, or 

 inclined, folds the opposite limbs have different angles of dip, the 

 axial plane is oblique and divides the flexure into more or less dis- 

 similar parts. When one limb has been pushed over past the per- 

 pendicular, the fold is said to be overturned or inverted, and when 







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Fig. 97. — Symmetrical, closed anticline: near Quebec, Canada. (U. S. G. S.) 



this has gone so far that one of the limbs becomes nearly or quite 

 horizontal, the fold is recumbent. 



According to the second mode of classification, we have a some- 

 what different series of terms ; but both methods have their uses 

 and must be employed. Open folds are those in which the limbs 

 are widely separated ; strata with open, gentle flexures are said to 

 be undulating. Closed folds are those in which the limbs of the 



