THE MAKING OF MOUNTAINS 37 



A mountain-range may be so simple that it consists 

 just of one broad saddleback (anticline) of arched beds 

 or strata of rock; or there may be a series of saddle- 

 backs with troughs (synclines) between. But matters 

 are rarely so simple as this. The folds become folded 

 and merged with one another, they are overturned and 

 broken, and great sheets of rock hundreds or thou- 

 sands of feet thick may be thrust over younger rocks 

 for many miles. Then, again, the results of unequal 

 weathering may greatly disguise the original folding. 

 It is only after much hard study that we can read the 

 story of a mountain range for ourselves. Thus, to 



DIAGRAM OF MUCH-WEATHERED SADDLEBACKS (ANTICLINES) AND 

 TROUGHS (SYNCLINES), DUE TO FOLDING OF THE EARTH'S 

 CRUST. 



Similar strata are similarly shaded. 



take a simple case, it often comes about that an original 

 saddleback or anticline coincides with the valley of 

 to-day and a trough or syncline with the hill. Another 

 caution to be borne in mind is that the intense pres- 

 sure which has brought about mountain-folding, as 

 the outcome of subterranean changes, must often have 

 produced great heat. As the result of this heat the 

 rocks became plastic, and as another result their 

 original composition and texture were often pro- 

 foundly altered. Rocks laid down in the form of sedi- 

 ment sandstone, for instance may be changed 

 ("metamorphosed") into crumpled and gnarled 

 schists ; limestone may be changed into marble ; ancient 



