THE ORIGIN OF MOUNTAINS. 69 
thrust to one side, it is said to be inclined or re- 
cumbent (Fig. 12). 
Where strata are thrown into folds the convex 
portion is termed an anticlinal (Fig. 14, A) and the 
concave a synclinal (Fig. 14, B). The same terms 
are applicable when the surface has been planed 
down so that the strata would dip as in Fig. 13. 
The inner strata of any fold are called the core, 
those of an anticlinal (Fig. 14, A) being called the 
arch core, those of a synclinal (Fig. 14, B) the trough 
cere. 
Fig. 14. — Diagram showing Anticlinal and Synclinal Folds. 
It is obvious of course that when strata are 
thrown into such folds, they will, if strained too 
much, give way at the summit. Before doing so, 
however, they are stretched and consequently 
loosened, while on the other hand the strata at the 
bottom of the fold are compressed; the former, there- 
