420 



FIRST TEAR SCIENCE 



where the folds are least high, streams cut across them 

 and pass from one trough to another. Along these trans- 

 verse stream courses are usually built the roads that cross 

 the ridges. 



Sometimes the tops of the ridges have been sufficiently 

 worn away or are broad enough to form considerable flat 

 areas, where little villages are situated. But most of the 

 population is found along the longitudinal valleys, espe- 



FOLDED STRATA. 



cially where there are cross valleys. Some of the cross 

 streams seem to have no connection with sags in the folds, 

 but appear to have cut their valleys through the folds as 

 fast as they rose, thus indicating that the rate of folding 

 was slow. 



198. Massive Mountains. The mountains already studied 

 are all comparatively low. Probably none of them rises to 

 a height exceeding 6000 feet. They are simple in form 



