314 LAND SCULPTURE 



their own weight, and masses fall from the face of the cliff, thus 

 maintaining the verticality. The talus blocks form a slope, con- 

 necting the successive cliffs by gentler inclines. The Uinta 

 Mountains in northern Utah are formed by a great anticlinal 

 arch, so broad and gently curved that in a given section the 

 strata appear almost horizontal. Out of these immensely thick 

 and nearly level masses the atmospheric denuding agencies have 

 carved an infinite and most picturesque variety of peaks, pin- 

 nacles, columns, and amphitheatres, while the streams have cut 

 profound and gloomy canons. Vast talus slopes remain to indi- 

 cate the amount of destruction. 



Inclined or tilted strata give rise to a different class of topo- 

 graphical forms. If, as is generally the case, harder and softer strata 

 alternate, the latter will be swept away more rapidly than the 

 former, which are left standing as ridges or cliffs, the height and 

 steepness of which are determined by the thickness and inclina- 

 tion of the more resistant rocks. In case the strata are steeply 

 inclined, a succession of hard beds alternating with soft will 

 give rise to a series of ridges and valleys, the slopes of which 

 depend upon the angle of dip. If the beds are standing in a 

 vertical position, the two slopes of each ridge will be nearly equal, 

 the hard strata forming the backbone of the ridge and the softer 

 ones the sloping sides. As the inclination departs from verticality, 

 the more unequal do the two slopes of each ridge become the 

 longer and gentler one being in the direction of the dip. Ridges 

 and valleys of this class are beautifully exemplified in the Appa- 

 lachian Mountains. Figure 25 shows Kittatinny Mountain, through 

 which the Delaware River has cut the famous Water Gap ; the 

 crest of the ridge is formed by very hard and indestructible 

 sandstones and conglomerates, while the valley is in slates. 



In gently inclined strata the abruptly truncated and cliff-like out- 

 crops of the hard strata are called esca7-pments, and follow, with some 

 irregularities and sinuosities, the strike of the beds. Whether the 

 general course of the escarpment shall be straight or curved will, 

 therefore, be determined by the constancy or change in the direc- 

 tion of the dip ; for, as we have already learned, the strike changes 



