CONTORTIONS OF THE STRATA 



51 



of the plunging anticline, where they disappear below the surface 

 in the axis, will present a domed surface sloping forward like the 

 back of a whale as it rises above the surface of the sea. Plunging 

 folds in series will thus appear in the topography as a series of 

 sharply zigzagging ranges at those localities where the harder 

 layers intersect the surface. Such features are encountered in 

 eastern Pennsylvania, where the hard formations of the Appala- 

 chian Mountain system plunge northeastward under the later 

 formations. The pitch of the larger fold is often disclosed by that 

 of the minor puckerings superimposed upon it. 



The meaning of an unconformity. The rock beds, which are 

 deposited one above the other during a transgression of the sea, 



FIG. 33. Unconformity between a lower and an upper series of beds upon the coast 

 of California. Note how the hard layer stands in relief upon the connecting 

 surface (after Fairbanks). 



are usually parallel and thus represent a continuous process of 

 deposition. Such beds are said to be conformable. Where, upon 

 the other hand, two series of deposits which are not parallel to 

 each other are separated by a break, they are said to form un- 

 conformable series, and the break or surface of junction is an un- 

 conformity (Fig. 33). 



