138 STRUCTURAL AND FIELD GEOLOGY 
25). Ina foldofthis kind the strata which form its lower limb 
are necessarily turned upside down, and hence the structure 
FIG. 25. —UNSYMMETRICAL FLEXURES: OVERFOLDS. 
is frequently termed Inversion. Unsymmetrical and closely 
compressed symmetrical folds not infrequently occur together, 

Fic. 26.—ISOCLINAL FOLDS. 
but in regions of highly inclined and vertical strata the 
flexures are usually unsymmetrical, and for the most part 

FIG. 27.—ISOCLINAL FOLDS, MUCH DENUDED. 
are overfolds. In such cases the successive axial planes 
very often incline for long distances in the same direction— 

