

\TION OF STRATA 



ami unconformably covered by, the upper horizontal 

 strata. 



'Inhere occur wide tractt of country where the under 

 rocks have been to violently disturbed, that for 

 wiles they seem to be standing on end. In such cases, it is 

 usual to find some one prevalent direction of strike along 

 \hu-h the vertical or highly inclined beds range them- 

 telves. And a careful examination will generally disclose 

 proofs that the strata really consist of many rapid folds, 

 the same beds being repeated again and again, Sub- 





sequent extensive denudation has worn away the tops of 

 the arches and produced a form of surface whirl. 

 have little or no reference to the structure of the rocks 

 below (Fig. 49). 



Rocks contorted in this way are pretty sure to present 

 cases of isoclinal folds, that is, the axes of the curves are 

 not vertical but inclined In Fig. 50, for example, the 

 folds are all inclined in the same direction, so that in 

 each of them one half of the curve has its strata turned 

 bottom upjxrrmost. Inversions on a grand scale are to 

 be seen in great mountain -chains like the Alps. The 

 accompanying drawing (Fig. 51) represents a very re- 



