Ch. V.] 



CUEVED STEATA EST THE ALPS. 



Fig. 8L 



59 



Unterseen and Grindelwald, curves of calcareous shale are seen from 

 1000 to 1500 feet in height, in which the heds sometimes plunge down 

 vertically for a depth of 1000 feet and more, before they bend round 



Fig. S2. 



Curved strata of the Iselten Alp. 



again. There are many flexures not inferior in dimensions in the Pyre- 

 nees, as those near Gavarnie, at the base of Mount Perdu. 



Unconformable stratification. — Strata are said to be unconformable, 

 when one series is so placed over another, that the planes of the superior 

 repose on the edges of the inferior (see fig. 83). In this case it is evi- 



Fig. 83. 



Unconformable junction of old red sandstone and Silurian schist at the Siccar Point, near St. Abb's 

 Head, Berwickshire. See also Frontispiece. 



dent that a period had elapsed between the production of the two sets 

 of strata, and that, during this interval, the older series had been tilted 



