796 



PRINCIPLES OF STRATIGRAPHY 



Anticlines and synclines may be either symmetrical or asym- 

 metrical, according as the limbs are equal in length and inclination, 

 or unequal. Anticlines may be erect or recumbent. In the latter 

 case one limb of the anticline is overfolded, and the strata compos- 

 ing it are overturned. 



«>'"' 



Fig. 176. Anticlinal fold near St 

 Abbs Head, Scotland. (Geikie.) 



i*i*U «,^ 





Fig. 177. Two anticlines enclosing a 

 s y n c 1 i n e truncated above. 

 (Geikie.) 



(c) Isoclines. When the limbs of a fold are parallel an isocline 

 is produced. The limbs of such a fold may stand vertically or they 

 may be inclined. In the latter case some portion of the strata in- 

 volved will always be overturned, i. e., their original surface now 



Fig. 178. Synclinal fold near Banfif, Scotland. (After Geikie.) 



lies below. Nearly horizontal isoclines are produced by overfolds 

 and underfolds. 



In a region of isoclinal folds, the most important problem con- 

 fronting the stratigrapher is the recognition of the repetition of 

 strata and the proper relationship between them. It is evident that 

 a succession of strata, such as is shown in Fig. 179, a, may be inter- 



