CLIFFS AT THE MOUNTAIN BASE 213 



and graded front of the mountains by the less orderly forms that char- 

 acterize the piedmont slope toda}^. 



The Fault Scarp 



The well carved mountain front and the uneven piedmont slope are 

 separated by a line of low cliffs, here interpreted as a fault scarp. The 

 location of the cliffs on or close to the line of strong faulting, shown by 

 Viola to separate the Cretaceous mountain mass from the Eocene pied- 

 mont slope, is very suggestive of dislocation ; and the freshness of the 

 cliffs shows their origin to have been recent, much more recent than the 

 great dislocation in consequence of which the mountain front was ex- 

 posed to the forces of denudation and elaborately carved into buttresses 

 and ravines. The cliffs are not perfectly continuous or of uniform height ; 

 they weaken in some places to ledges of only 10 or 15 meters; they rise 

 in crossing some of the rock fans to bold walls 30 or 40 meters high. 

 Their line of extension is comparatively straight between Scurgola and 

 Morolo, but it is sometimes locally divided into several branches, each 

 marked by low scarps. Where the cliffs are highest nearly all the recent 

 dislocation seems to have been accomplished on a single plane of move- 

 ment. In a few places shortly south of Scurgola there is an appearance 

 of fault scarps on the mountain front 50 or 100 meters above its base, 

 the distinction between these supposed fault faces and the normal out- 

 crops of ungraded ledges being that while the latter follow the stratifica- 

 tion, contouring forward around the buttresses and returning into the 

 ravines, as already stated, the former follow a nearly vertical plane, and 

 therefore rise and fall in passing the salient front of a buttress. All 

 these minor features are, however, but natural complications of the main 

 scarp, by which the graded slopes of the mountain front are broken at 

 their base into a precipitous descent to the piedmont slope. When seen 

 in profile (plate 18, figures 1 and 2), the discontinuity of the slopes is often 

 very marked ; it is much stronger than the steps caused by any outcrop- 

 ping, ungraded ledges in the lower or middle part of the mountain front, 

 and is possibly equaled only in the stronger cliffs of the mountain tops. 

 Most striking is the prevailing increase in the height of the scarps as 

 they pass in front of the ravines, where the arched cliff tops display to 

 a nicety the convex form of the rock fans. The cliff beneath the third 

 ravine northwest of Morolo is the finest example of this kind; it is 

 pictured from the front and side in plate 19, figures 1 and 2. The scarp 

 persistently increases in strength while passing the ravines. It may be 

 concluded from the varying height of the cliffs and the irregular forms of 



