DAVIS: THE GRAND CANYON OF THE COLORADO. 145 



the canyon cycle, however recent the latest of its movements may have 

 been on the brink of the canyon. 



Topographic Effects of Faulting obliterated or reversed by Erosion. — 

 The continuously graded platform, sloping gently eastward across the 

 fault line near Pipe spring and obliterating the topographic effects of 

 faulting, has already been described. The fact that this platform is 

 now gaining drainage at the expense of the west-sloping platform, 

 strongly suggests a remote date for the displacement ; had a recent 

 movement taken place here, with uplift on the east, the westward mi- 

 gration of the divide could hardly be explained. A little further south, 

 the Shinarump cliffs in the Uiukai'et block, west of the fault line, over- 

 look lower ground east of them, thus furnishing an excellent example of 

 topographical relief standing in opposition to the displacement of the 

 fault ; evidently the result of the long action of erosion upon the unlike 

 strata brought together by the faulting. Indeed, this part of the fault 

 line offers many instructive illustrations of the difference between the 

 geological and the geographical values of a fault. Geologically con- 

 sidered, the fault has a fixed value ; geographically considered, the 

 fault has a changing value. When the fault attains its full displace- 

 ment, its geological history is completed, and its geological measui-e 

 thenceforward remains constant. When the fault attains its full dis- 

 placement, its geographical history is just begun, and thereafter its 

 measure perpetually changes. The topographic features initiated by 

 displacement may be more or less modified by contemporaneous erosion, 

 but the young fault cliff will still be a tolerably regular feature, scored by 

 growing ravines. Movement ceasing, erosion continues and the fault-cliff 

 becomes lower and less regular. Where hard beds in the heaved block 

 confront weak beds in the thrown block, the cliff consequent on fault- 

 ing will last longest ; where these hard beds are not underlain by weak 

 beds (uuless beneath baselevel), the cliff face will retreat most slowly 

 from the fault line. Where weak beds are brought together, all topo- 

 graphical indication of the fault will soon disappear. Where hard beds 

 in the thrown block confront weak beds in the heaved block, the topo- 

 graphic relief may come to contradict the throw of the fault, as is the 

 case with the Shinarump cliffs above mentioned. But in time, all indi- 

 cation of the fault will be obliterated in the general reduction of the 

 region to a peneplain, strong and weak rocks alike being laid low. If 

 a general uplift of the region then occur, erosion may renew the fault- 

 cliff topographically wherever strong beds adjoin weak ones, although no 

 new movement takes place upon the fault plane. In such cases, the small 



